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Folks,

Submarine Torpedo Fire Control Manual, is a training and reference manual from 1952. It describes how to plan a submarine's approach and attack using the fire control systems on Fleet and Guppy submarines with straight running torpedos (without homing, wire guidance, etc.). It represents the submarine fire control problem of WW II and the immediate post war period.

In this online version of the manual we have attempted to keep the flavor of the original layout while taking advantage of the Web's universal accessibility. Different browsers and fonts will cause the text to move, but the text will remain roughly where it is in the original manual. In addition to errors we have attempted to preserve from the original, this text was captured by a combination of optical character recognition and human typist. Each method creates errors that are compounded while encoding for the Web. Please report any typos, or particularly annoying layout issues to the Mail Feedback Form for correction.

Thank you to the Wisconsin Maritime Museum, USS Cobia for providing a photocopy of the manual.

Richard Pekelney
Webmaster


CONFIDENTIAL
(non registered)
SLM 1

SUBMARINE

TORPEDO FIRE CONTROL

MANUAL

 

COMMANDER SUBMARINE FORCE
UNITED STATES ATLANTIC FLEET
U.S.S. FLYING FISH, Flagship

 

MAY 1950

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SLM 1CONFIDENTIAL NONREGISTERED

COMMANDER SUBMARINE FORCE
UNITED STATES ATLANTIC FLEET
U.S.S. FLYING FISH (SS229), FLAGSHIP

18 April 1950

LETTER OF PROMULGATION

1. The Submarine Torpedo Fire Control Manual is a nonregistered Confidential publication and shall be transported, handled, and stowed as prescribed by U.S. Navy Regulations and the Registered Publications Manual.

2. This Manual has been prepared by officers of the Submarine School to be used as a text for the officers Basic Submarine Tactical and Prospective Commanding Officers courses of the Submarine School. It is issued to the Submarine Force, U.S. Atlantic Fleet as a suitable guide in organizing and operating a Torpedo Fire Control party. The terminology and procedures should be considered as standards wherever material and personnel allowances permit. The doctrine expressed in this Manual is considered to be excellent but not mandatory. Its use, as always, is dependent upon the existing situation and the judgement of the Commanding Officer.

3. Comments and recommendations are invited for correction and revision in 1952.

4. THIS DOCUMENT CONTAINS INFORMATION AFFECTING THE NATIONAL DEFENSE OF THE UNITED STATES WITHIN THE MEANING OF TITLE 18, U.S.C., SECTIONS 793 AND 794. ITS TRANSMISSION OR THE REVELATION OF ITS CONTENTS IN ANY MANNER TO AN UNAUTHORIZED PERSON IS PROHIBITED BY LAW.

5. IT IS FORBIDDEN TO MAKE EXTRACTS FROM OR TO COPY THIS PUBLICATION WITHOUT SPECIFIC AUTHORITY FROM THE CHIEF OF NAVAL OPERATIONS EXCEPT AS PROVIDED FOR IN ARTICLES 9-9 AND 9-10 U.S. NAVY SECURITY MANUAL FOR CLASSIFIED MATTER.

6. This publication may be carried for use in aircraft.
JAMES FIFE, Rear Admiral, U.S. Navy, Commander Submarine Force, U.S. Atlantic Fleet

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CONFIDENTIAL
(non registered)
SUBMARINE TORPEDO
FIRE CONTROL MANUAL

DISTRIBUTION

CNO 50
CinClantFlt 1
ComSubPac 100
ComSubRon TWO 1
ComSubRon FOUR 1
ComSubRon SIX 1
ComSubRon EIGHT 1
ComSubDevGru TWO 1
ConiSubDiv TWENTY-ONE 1
CouiSubDiv TWENTY-TWO 1
ComSubDiv FORTY-ONE 1
ComSubDiv FORTY-TWO 1
ComSubDiv SIXTY-ONE 1
ComSubDiv SIXTY-TWO 1
ComSubDiv EIGHTY-ONE 1
ComSubDiv EIGHTY-TWO 1
Each SS SubLant 1
CO USS ORION (AS18) 1
CO USS H.W. GILMORE (A516) 1
CO USNavSubBase, NewLon 1
CO USNavSubScol, NewLon 400
SubLant Reserve Coordinator 600
Spares, SubLant 286

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CONFIDENTIAL
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SUBMARINE TORPEDO
FIRE CONTROL MANUAL

An empty table of Record of Corrections. Change No., Date Entered, Signature of Officer Making Correction

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LIST OF EFFECTIVE PAGES
(Reverse of all sheets blank)

Subject Matter Changes in effect Page Numbers
Title Page Original i
Letter of Promulgation Original ii
Distribution List Original iii
Record of Corrections Original iv
List of Effective Pages Original v
Table of Contents Original vi,vi(a)
List of Illustrations Original vii
Forward Original viii
Chapter 1 Original 1-1 to 1-13
Chapter 2 Original 2-1 to 2-11
Chapter 3 Original 3-1 to 3-4
Chapter 4 Original 4-1 to 4-6
Chapter 5 Original 5-1 to 5-54
Chapter 6 Original 6-1 to 6-11
Chapter 7 Original 7-1 to 7-7
Chapter 8 Original 8-1 to 8-14
Chapter 9 Original 9-1 to 9-11
Chapter 10 Original 10-1 to 10-6
Chapter 11 Original 11-1 to 11-2
Illustrations Original PLATES I - XXIV

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TABLE OF CONTENTS

Pages
Chapter 1 - Definitions 1-1 to 1-13
Chapter 2 - Phraseology 2-1 to 2-11
Chapter 3 - Submarine Submerged Characteristics 3-1 to 3-4
Fleet Type Submarine 3-1 to 3-3
Guppy II Type Submarine 3-3 to 3-4
Chapter 4 - The-Torpedo Fire Control Party 4-1 to 4-6
Chapter 5 - Duties of the Fire Control Party 5-1 to 5-54
The Approach Officer 5-1 to 5-22
   The Periscope 5-1 to 5-10
   Periscope Ranging 5-3 to 5-8
   Target Length 5-8 to 5-10
   Periscope Technique 5-10 to 5-13
   Periscope Procedure 5-13 to 5-16
   Duties 5-16 to 5-17
   Periscope Observations 5-17 to 5-19
   Plan of Attack 5-19 to 5-21
   Ship Handling 5-21 to 5-22
   Coordination of Fire Control Party 5-22
The Attack and Sonar Coordinator 5-22 to 5-24
The TDC Operator 5-24 to 5-29
The Assistant TDC Operator 5-30 to 5-32
The Navigational Plotter 5-32 to 5-42
The Periscope Assistant 5-42
The Sonar Plotter 5-42 to 5-51
   Bearing Rate Plot 5-43 to 5-46
   Bearing Difference Plot 5-46 to 5-51
The Firing Key Operator 5-51 to 5-52
The Gyro Angle Setter 5-52 to 5-54
Chapter 6 - Spreads 6-1 to 6-11
Types of Spreads 6-7 to 6-8
Computed Spread 6-8 to 6-9
4-3-2-1 Spread 6-9 to 6-10
Spread Policy 6-10
Determination of Coverage 6-11
Chapter 7 - Firing Methods 7-1 to 7-7
Check Bearing Method 7-2 to 7-3
Continuous Bearing Method 7-4 to 7-5
Constant Bearing Method 7-5 to 7-6
Chapter 8 - Theory of Approach and Attack 8-1 to 8-14
Basic Fundamentals of the Approach and Attack 8-1 to 8-8
   Determination of Direction of Target Motion 8-1 to 8-4
   Speed Determination 8-4 to 8-5
   Relative Movement 8-5 to 8-8
Analysis of Torpedo Firing 8-8 to 8-11
Analysis of Torpedo Track Angles 8-11 to 8-12
Down the Throat Shot 8-12 to 8-13
Deflection Angle for Straight Fire 8-13

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TABLE OF CONTENTS

Pages
Chapter 9 - Submerged Approach and Attack Tactics 9-1 to 9-11
The Contact Phase 9-1 to 9-2
The Approach Phase 9-2 to 9-5
The Attack Phase 9-5 to 9-11
Chapter 10 - Theory of the Periscope Approach and Sonar Attack 10-1 to 10-6
Chapter 11 - Submerged Approach and Sonar Attack Tactics Against Surface Targets 11-1 to 11-2

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LIST OF ILLUSTRATIONS

Subject matter Plate Number
Definitions I
Periscope Field - TELEMETER SCALE II
Range Omnimeter - RANGES III
Stadimeter RANGES IV
Range Omnimeter - TARGET LENGTH V
Periscope-Radar PLOT VI
Stadimeter PLOT VII
Radar Tracking PLOT VIII
Bearing Rate PLOT IX
Bearing Rate Plot Recorder's Form X
Bearing Difference Plot - Scale 20 XI
Bearing Difference Plot - Scale 10 XII
Bearing Difference Plot Data XIII
Bearing Difference Plot Data XIV
Spreads XV
Relative Movement XVI
Analysis of Curved Fire - 46 Kt. Torpedo XVII
Analysis of Curved Fire - 29 Kt. Torpedo XVIII
Approach and Attack Doctrine XIX
Situation Analysis, SITUATION I, First Course of Action XX
Situation Analysis, SITUATION I, Second Course of Action XXI
Situation Analysis, SITUATION II XXII
Situation Analysis, SITUATION III XXIII
Situation Analysis, SITUATION IV XXIV

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FOREWORD

Our submarines during and since the last war have demonstrated their ability to accomplish a variety of special missions of which they had previously been considered incapable. Many of them have been so altered that the accomplishment of these missions have become their primary duties. The primary mission of the true submarine, however, remains, today as it has always been, the delivery of successful torpedo attacks against the ships of an enemy.

The types of targets which a submarine may encounter are many and varied, i.e., single unescorted merchantmen, single destroyers, submerged submarines, unescorted group of ships, convoys, and task forces. The variety of targets and other unpredictable conditions, such as weather and depth of water, render it impracticable to set forth a procedure or doctrine which will apply under all conditions. The submarine Commanding Officer must rely mainly on his own judgement and experience to insure the completion of a successful attack.

There do exist, however, tested and proved procedures and tactics which if followed will assist the submarine Commanding Officer and increase his chances of success. It is the purpose of this book to present to the officers of the Submarine Force under one cover the best known principles of Submarine Fire Control Organization and Torpedo Attack Tactics.

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CHAPTER 1

DEFINITIONS

100. ANGLE ON THE BOW: The angle between the line of sight and the target's bow measured to port or starboard of the target's bow from 0 degrees to 180 degrees. Symbol: Ab. See Plate I, figure 1.

101. APPROACH PHASE

The period during which the submarine maneuvers to close to a position for commencing the Attack Phase.

102. APPROACH COURSE

The course or courses taken by the submarine during the Approach Phase.

103. ATTACK PHASE

The period during which the submarine maneuvers for a firing position.

104. COVERAGE

The ratio of the angular or linear distance between the wing torpedoes of a salvo to the angular or linear length of the target corrected for the torpedo track angle.

EXAMPLE: Target length = 600 feet 6 degrees at 2000 yards on a 90 degrees torpedo track. A salvo of 6 torpedoes with a unit of spread of 2 degrees would produce a coverage of (10 degrees / 6 degrees) = 167%. For

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a torpedo track of 30 degrees the angular length of the target is 3 degrees (reduced by sine 30 degrees = 0.5). The same unit of spread as above would produce a coverage of (10 degrees / 3 degrees) = 333%

105. CRITICAL RANGE:

The range at which the submarine normally passes from the Approach Phase to the Attack Phase. It is equal to a 7 1/2 minute run of the target, and may be easily obtained by dividing the target's speed by 4 and multiplying by 1000. Example: Critical range for a 12 knot target is 3000 yards.

106. DEFLECTION-ANGLE:

The angle between the periscope angle and the component of the gyro angle of the torpedo determined only by track angle, torpedo speed, and target speed. See Plate I, figure 3.

NOTE The excluded portion of the gyro angle is that due to the tactical characteristics of the torpedo and the torpedo tube parallax.

107. DISTANCE TO THE TRACK:

The perpendicular distance from the submarine to the target's track extended. See Plate I, figure 1.

108. DIVERGENT SPREAD:

A spread in which the torpedoes of a salvo intersect the target's track at different points along the target's

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length and at different torpedo track angles.

Diagram showing three torpedo tracks to bow, mid and stern of target.
NOTE: This spread is produced by applying an angular offset to each torpedo.

109. FIRING COURSE

The course of the submarine at the instant of firing.

110. GENERATED BEARING

Relative target bearing obtained from TDC position keeper section Relative Target Bearing dial usually given on "Up scope".

111. GYRO ANGLE

The angle between the longitudinal axis of the submarine and the final torpedo track measured right or left of the bow or stern (bow for bow shots, stern for stern shots) of the submarine from 0 degrees to 180 degrees. See Plate I, figure 3.

NOTE: This angle consists of the algebraic sum of the periscope angle, the deflection angle, the torpedo tube parallax angle, and the angular correction for the tactical characteristics of the torpedo.

112. GYRO ANGLE ORDER:

The angle between the longitudinal axis of the

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submarine and the final torpedo track measured clockwise from the bow of the submarine from 000 degrees to 360 degrees.
NOTE: This is the same as Gyro Angle except that it is measured clockwise from the bow from 000 degrees to 360 degrees.

Ilustration of gyro angle, difference between torpedo track and ships course.

113. INTERCEPT POINT:

The point at which the torpedo crosses the target track. See Plate I, figure 3.

114. LEAD ANGLE

The angle between the true bearing of the target and the true course of the submarine (or submarine course reversed for stern tube shots).

Illustration of lead angle, difference between own ships course and target bearing.

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115. LONGITUDINAL SPREAD:

A spread in which the torpedoes of a salvo intersect the target's track at different points along the target's length but at the same point on the target's track, and at the same torpedo track angles.

NOTE: This spread is produced by the motion of the target across the line of sight, since succeeding torpedoes run down the wake of the first torpedo fired.

Illustration of longitudinal spread with single torpedo track angle.

116. NORMAL APPROACH COURSE:

The course which is equal to the true bearing of the target, plus or minus 90 degrees in the direction to close the target's track. See Plate I, figure 1.

NOTE When on the NAC the relative bearing of the target is 090 or 270. Symbol: NAC.

117. NORMAL COURSE:

The course at right angles to the target's course in the direction to close the target's track.

NOTE The same as the course for a 90 degree track angle. Symbol: NC.

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118. OPTIMUM APPROACH COURSE:

The Normal Approach Course with an imaginary target moving along the same course, and at the same speed as the actual target, but on the beam of the actual target at a range equal to the limiting torpedo run on the side closest to the submarine. Symbol: OAC.

Illustration of Optimum Approach Course

119. OPTIMUM TORPEDO TRACK ANGLE:

The torpedo track angle for which expected errors in target course produce the least change in the deflection angle. See Plate I, figure 2.

120. PARALLAX CORRECTION SONAR

The algebraic sum of the angular correction compensating for the longitudinal distances between the sonar equipment and the periscope (P1), the center of the target and its propellers (P2), and the initial and developed positions of the target during the transmission of the sound waves.

NOTE The factors of Sonar Parallax Base

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Line and the Target length are constant insofar as their Linear values are concerned. The angle resulting from the initial and developed positions of the target during sound transmission varies with target speed and range.

Illustration demonstrating Parallax correction for sonar.

121. PARALLAX CORRECTION TORPEDO TUBE:

The angular correction compensating for the longitudinal distance between the muzzle doors and the periscope. See Plate I, figure 4.

NOTE This is different for each tube nest.

122. PARALLAX HIGH:

The torpedo advance is opposed to the general direction of target motion.

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Illustration of high target parralax.

123. PARALLAX LOW:

The torpedo advance is in the general direction of target motion.

Illustration of Low Parralax target angle.

124. PERISCOPE ANGLE:

The angle between the longitudinal axis of the submarine and the computed line of sight at the instant of firing established by the algebraic sum of the

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deflection angle, the gyro angle, the torpedo tube parallax correction, and the angular correction for the torpedo tactical characteristics. It is measured clockwise from the bow of the submarine from 000 degrees to 360 degrees. (see Plate I, figure 3).

NOTE: In a continuously generating problem such as that presented on the TDC, the Periscope Angle is the relative target bearing at the instant of firing.

125. PSEUDO TORPEDO RUN:

The distance in yards between the periscope position at the instant of firing and the point of intercept. (See Plate I, figure 3).

126. REACH:

The initial straight path of the torpedo, measured in yards. Symbol: M. (See Plate I, figure 3).

127. REACH AND TURNING RADIUS CORRECTION:

An angular correction applied to a computed deflection angle, in angled shots, to correct for the reach (N) and the turning radius (z) of the torpedo in proceeding to its final track.

NOTE: This is computed by the angle solver.

128. SALVO:

A number of torpedoes fired at short-intervals at the same target.

129. SPREAD:

Offset angle or change in target bearing applied to

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the gyro angle order of each torpedo of a salvo to cause successive torpedoes to hit at different points along the target length or track extended.
NOTE: An offset angle is used in a divergent spread, whereas the linear spread in a longitudinal spread is accomplished by changing the point of aim.

130. SPREAD ANGLE:

The additional gyro angle, over that required for hitting the same point of a moving target, applied to successive torpedoes for producing the desired spread.

Illustration of three different angle tracks.


Spread Angle: Angles BAC, EAF
Target Advance Angle: Angles CAD, DAE
Unit of Spread: Angles BAC, EAF

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131. TARGET ADVANCE ANGLE:

The angular motion of the MOT of the target between successive torpedoes. (See sketch on preceding page).

132. TORPEDO ADVANCE:

The perpendicular distance between the torpedo final course and a line through the tube muzzle parallel to the torpedo final course. (See Plate I, figure 3)

NOTE: Result of reach and turning radius.

133. TORPEDO RUN:

The total distance in yards traveled by the torpedo from the tube to the target. (See Plate I, figure 3)

134. TORPEDO RUN DIFFERENCE:

The actual torpedo run for a given time minus the distance the torpedo would have traveled during the same time at corrected torpedo running speed (final running speed), in yards. Symbol: Uy.

135. TORPEDO RUNNING SPEED CORRECTED:

The uniform running speed in knots of the torpedo under any given conditions after the initial acceleration is completed. Symbol: S'z.

136. TORPEDO TURNING RADIUS:

The radius of the circular track, in yards, of the torpedo from the end of the initial straight path to the beginning of the final straight path. Symbol Z. (See Plate I, figure 3).

137. TRACK ANGLE:

The angle at the point of intercept between the

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target ships course and the submarine's course measured to port or starboard of the target ship's bow toward the submarine. Symbol: Ta. (See figure under torpedo Track Angle).

138. TORPEDO TRACK ANGLE:

The angle at the point of intercept between the target ships course and the reverse of the torpedo's course, measured to port or starboard of the target's bow. Symbol: TTa.

Illustration of track angle.

139. TORPEDO TUBE PARALLAX BASE LINE:

The longitudinal distance between the tube muzzle and the periscope. Symbol: P. (see Plate I, fig. 4)

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140. UNIT OF SPREAD:

The offset angle or linear distance along the target's length or track between adjacent torpedoes of a salvo. (See sketch on preceding page).

141. VOLUME OF FIRE:

The number of torpedoes in a salvo.

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CHAPTER 2

PHRASEOLOGY

200. STAND BY FOR OBSERVATION (LOOK AROUND (LOOK AT ESCORTS):

A preliminary order given by the Approach Officer to alert the Fire Control Party and inform them of the reason the periscope is to be raised.

201. UP SCOPE:

An order from the Approach Officer to the Periscope Assistant to raise the periscope. This may be combined with a hand signal should the Approach Officer so desire.

202. PUT ME ON:

An order from the Approach Officer to the Periscope Assistant to place the periscope on the generated target bearing.

203. BEARING - MARK:

A phrase used by the Approach Officer or by one of the Radar or Sonar Operators indicating to all members of the Fire Control Party that the target bearing as read on the various repeaters is correct. This is usually paralleled by a buzzer and mark light.

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204. RANGE - MARK:

A phrase which when used by the Approach Officer during a periscope observation directs the Periscope Assistant to read the stadimeter or telemeter range and informs the Fire Control Party of the time of the range. When spoken by the Radar Operator it indicates that the radar is on the target and the range repeaters are reading correctly. It is usually paralleled by a buzzer and a mark light in the latter case.

205. TDC MATCHED:

A phrase used by the TDC Operator during the initial observation to inform the Approach Officer that the TDC is matched in bearing and range.

206, ANGLE ON THE BOW PORT (STARBOARD):

A phrase used in stating the angle on the bow of some designated ship, whether it be target or escort. It is usually spoken by the Approach Officer after an observation arid while the periscope is being lowered. Note that the side of the angle is stated before its value.

207. TARGET HAS ZIGGED TO HIS RIGHT (LEFT):

A phrase used to notify all members of the Fire Control Party that the target group has changed course. When spoken by the Approach Officer following a periscope observation it should be followed by a statement of the new Angle on the Bow.

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208. TARGET IS ZIGGING TO HIS RIGHT (LEFT)

A phrase used to notify all members of the Fire Control Party that the target group is changing course. Then spoken by the Approach Officer following a periscope observation it is an order to the TDC Operator to change the target course in the TDC thirty degrees in the indicated direction.

209. GENERATED ANGLE ON THE BOW IS ____:

Report of TDC Operator after the Approach Officer has announced the observed angle on the bow when the generated angle on the bow is within 10 degrees of the observed angle on the bow.

210. INDICATES A ZIG OF ____:

Report of TDC Operator after Approach Officer has announced the observed angle on the bow if the difference between the observed and generated values is more than 10 degrees.

211. DOWN SCOPE:

An order from the Approach Officer to the Periscope Assistant directing him to lower the periscope all the way. In order to reduce conversation in the conning tower during an approach the order may be given by merely raising the periscope handles.

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212. DIP SCOPE:

An order from the Approach Officer to the Periscope Assistant directing him to lower the periscope until the periscope head is under water. This may be given by holding the hands in a horizontal position following a hand signal to lower the periscope.

213. PIP - NO PIP:

A phrase used by the ST radar operator when the periscope breaks water to inform the members of the Fire Control Party and the Approach Officer that he can or cannot obtain a range of the target.

214. SET DEPTH ____ FEET SPEED HIGH (LOW):

An order from the Approach Officer, relayed by the Firing Key Operator, to the Torpedo Tubes directing that the depth and speed spindles on the tubes be set as directed and the spindles withdrawn. The two orders are usually given as one but may be given separately.

215. TUBE ORDER FORWARD (AFT) IS ____:

An order from the Approach Officer to the Firing Key Operator designating the order in which the torpedo tubes are to be fired. It is also relayed by the Firing Key Operator to the Torpedo Tubes for their information.

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216. FLOOD (THE FORWARD)(THE AFTER)(TUBES NO._____)(ALL) TUBES:

An order from the Approach Officer, relayed by the Firing Key Operator to the Torpedo Tubes directing that the designated torpedo tubes be flooded from WRT Tank and be made ready to fire in all respects except for opening the outer doors.

217. OPEN THE OUTER DOORS:

An order from the Approach Officer, relayed by the Firing Key Operator to the Torpedo Tubes directing that the outer doors of tubes previously flooded be opened. The tubes should then be ready in all respects to fire.

218. GYROS FORWARD (AFT) MANNED:

A report from the Gyro Angle Setter to the assistant TDC Operator that his station is manned, gyro angle order is set on 000 (180 aft) and the gyro setter is in automatic.

219. GYROS FORWARD (AFT) MATCH GYROS IN AUTOMATIC:

An order from the Assistant TUC Operator to the Gyro Angle Setter to check his gyro setter in automatic and see that gyro angle order is matching.

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220. GYROS FORWARD (AFT) MATCHED IN AUTOMATIC (HAND):

A report from the Gyro Angle Setter to the Assistant TDC Operator, informing him that the gyro setting indicator regulator is matching the indicated value of gyro angle order.

221. GYROS FORWARD (AFT) STANDBY FOR GYRO CHECK - MARK:

An order from the Assistant TDC Operator to the Gyro Angle Setter to note the indicated gyro angle and report its value on the work "MARK".

222. GYROS FORWARD (AFT) SET GYROS _____:

An order from the Assistant TDC Operator to the Gyro Angle Setter to set the torpedo tube gyro spindles at some specific value. This is used only in an emergency caused by TDC failure and is given as a value between 000 and 360.

223. GYROS FORWARD (AFT) MATCH GYROS BY HAND:

An order from the Assistant TDC Operator to the Gyro Angle Setter to operate the gyro setting indicator regulator by hand and match gyros by the "follow the pointer method".

224. SECURE THE GYROS FORWARD (AFT).

An order from the Assistant TDC Operator to the Gyro Angle Setter to position the gyros on 000 (180 aft), place the gyro setter in automatic, and await further orders.

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225. USE (____PERCENT COVERAGE)(4,3,2,1)(SPECIAL METHOD) SPREAD:

An order from the Approach Officer to all members of the Fire Control Party in the conning tower which designates the type and amount of spread desired in a salvo of torpedoes.

226. SHOOTING WILL BE BY (CONSTANT BEARING)(CONTINUOUS BEARING)(CHECK BEARING) METHOD, BEARNG EVERY ___ TORPEDO:

An order from the Approach Officer to all members of the Fire Control Party in the conning tower which designates the firing method to be used.

227. CHECK BEARING:

An order from the Approach Officer to the Fire Control Party not to shoot another torpedo until another periscope bearing of the target has been observed and set in the TDC.

228. BEARING ON:

A phrase used by the Approach Officer when firing by the Continuous Bearing method to inform the Fire Control Party that the periscope is on the point of aim. When used by the TBT Operator it informs the TDC Operator that the TBT is on the designated target.

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229. BEARING OFF:

A phrase used by the Approach Officer when he desires to inform the Fire Control Party that the periscope is not trained on a previously designated point of aim. When used by the TBT Operator it informs the TDC Operator that the TBT is off the designated target.

230. FINAL BEARING AND SHOOT:

This is an order from the Approach Officer to all members of the Fire Control Party to commence shooting as soon as the next bearing (and range if immediately available) is obtained, set in the TDC, and the TDC "correct solution" light is on.

231. STANDBY FORWARD (AFT):

An order from the Approach Officer to the Firing Key Operator who relays it to the Torpedo Tubes, informing them that the tubes are to be fired and to be prepared to fire any tube by hand that does not fire electrically. This order is also relayed to the Control Room to alert the Diving Officer.

232. SET:

A phrase used by the TDC Operator to inform the assistant TDC Operator that the latest and best target information is set in the TDC and be is ready to commence shooting.

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233. SHOOT

An order from the Assistant TDC Operator to the Firing Key Operator to fire a torpedo. It also informs the Approach Officer that the designated spread is applied to the torpedo to be fixed and that the TDC correct solution light is on.

234. FIRE:

An order from the Approach Officer to the Firing Key Operator to fire the tube previously designated. It is used only when the torpedoes are being fired by the "Constant Bearing" method.

235. FIRE ONE (TWO) (THREE) (ETC):

An order from the Firing Key Operator to the Torpedo Tubes informing them that the designated tube is being fired in the Conning Tower and directing that it be fired by hand if it does not fire electrically.

236. ONE (TWO) (THREE) (ALL) TUBES FIRED FORWARD (AFT):

A phrase used by the Firing Key Operator to inform the Fire Control Party the number of torpedoes which have been fired,

237. CHECK FIRE:

An order from the Approach Officer to the Fire Control Party not to shoot any more torpedoes until directed to do so.

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238. SHUT THE OUTER DOORS FORWARD (AFT) (DESIGNATED TUBE):

An order from the Approach Officer directing that the torpedo tube outer door or doors be closed and that the pressure be vented off the tube or tubes. No other changes in the condition of the tubes are to be made.

239. SECURE THE TUBES FORWARD (AFT)(DESIGNATED TUBE):

An order from the Approach Officer to the torpedo tubes directing that the tubes be placed in the normal cruising condition.

240. TRACK TARGET BEARING (RIGHT HAND)(LEFT HAND):

An order from the Approach Officer or Sonar Coordinator directing a Radar or Sonar Operator to track the target designated.

241. TRACK IN HAND (ATF)(GTT):

An order from the Sonar Coordinator to a Sonar Operator directing him to place the training controls of the sonar head in the position indicated and keep the sonar head trained on the target.

242. SHIFT TO HAND (ATF)(GTT):

An order from the Sonar Coordinator to a Sonar Operator directing him to shift the training controls or the sonar head to the position indicated.

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243. GET A TURN COUNT:

An order from the Sonar Coordinator to a Sonar Operator directing him to count and report the propeller RPM of a designated target.

244. GET A PING RANGE:

An order from the Approach Officer or the Sonar Coordinator to a Sonar Operator directing him to obtain a sonar range of the target.

245. TAKE A SWEEP AROUND:

An order from the Approach Officer or the Sonar Coordinator to a Radar or Sonar Operator directing him to conduct a 360 degree search and report all contacts.

246. CONDUCT A FREQUENCY SEARCH:

An order from the Sonar Coordinator to a Sonar Operator directing him to conduct an all around listening search on all frequencies to determine if any vessels in the vicinity are conducting a supersonic search.

247. KEEP THE BEARINGS COMING:

An order from the Sonar Coordinator to a Sonar Operator directing him to report the bearing of the target as frequently as possible.

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CHAPTER 3

SUBMARINE SUBMERGED CHARACTERISTICS

300. GENERAL:

Submerged submarines are very much slower in their reaction to changes of speed and course than surface ships. This characteristic greatly affects the tactics of the approach and attack. For this reason all submarine officers should know the characteristics of their ship.

301. SUBMARINE TYPES:

The following discussion is divided into two parts, namely the Fleet Type Submarine and the Guppy II Type Submarine.

302 - 309. BLANK

310. FLEET TYPE SUBMARINE:

(a) The Fleet Type Submarine will make the following speeds submerged for the length of time indicated, if it starts with a full battery charge:

Knots Time
3.0 48 hours
6.0 3 hours
8.0 1 hour
9.0 1/2 hour

(b) Thus it can readily be seen that a major consideration when making an approach is conservation of the battery capacity.

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(c) In order to accelerate from 1/3 speed to the speeds indicated it will take the following time:

Speed Time
6.0 1:45 minutes
8.0 2:15 minutes
9.0 2:30 minutes

(a) In order to decelerate to 1/3 speed from the speeds indicated it will take the following time:

Speed Time
4.0 1:30 minutes
6.0 1:45 minutes
8.0 2:15 minutes
9.0 2:30 minutes

(e) It is interesting to note that it takes about the same amount of time to decelerate from 4 knots and 6 knots to 1/3. Thus when necessary to use speed it is just as well to use 6 knots as 4 knots as far as deceleration is concerned.

(f) The time it takes to decelerate may be decreased by backing the screws one third. The screws will act as a brake. The use of full rudder will tend to slow the submarine and may be used very effectively when decelerating. Full rudder decreases the speed through the water to about 3/4 of what would be made with the rudder amidships.

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(g) When making course changes greater than 20 degrees, full rudder should be used because a submarine is a very slow moving ship. The rudder should be taken off 20 degrees from the new course. The following rate of change of course for a submerged submarine at the various speeds can be expected.

Speed Rate
4 knots .45 deg/sec
8 knots 1 deg/sec

(h.) The tactical characteristics of a submerged fleet type submarine at 4 knots using 30 degrees rudder are as follows:

Advance 290 yards
Transfer 226 yards
Tactical Diameter 467 yards

311 - 319. BLANK

320. THE GUPPY II TYPE SUBMARINE:

(a) The Guppy II Type of submarine has characteristics different from the Fleet Type. The primary difference is submerged speed. The Guppy II will make the following speeds for the time indicated with a full battery, charge:

Knots Hours
4.3 48
5.3 36
6.3 20
8.2 10
9.4 6
9.9 5
11.8 3
15.7 1
17.8 30 minutes

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(b) In order to accelerate from 1/3 to the speed indicated it will take the following time:

Speed Time
8 knots 1:00 minute
12 knots 1:40 minutes
15 knots (series) 1:00 minute
17 knots (series) 1:40 minutes

(c) Deceleration to the following speed from flank will take the following time:

Speed Time
3 knots 4 minutes
8 knots 1:10 minutes
12 knots 0:15 minutes

(d) For approach work insofar as acceleration and deceleration are concerned it is of advantage to go to full speed. rather than standard if speed is desired for acceleration is faster and deceleration is almost equivalent to the point where the periscope may be used. The boat will decelerate faster by going to 1/3 speed (screws act as brake) rather than stop.

(e) At slow speeds turns are slightly faster than those made by the fleet type submarine. There is a marked improvement in ability to turn at the higher speeds.

Speed at StartTactical
Diameter
Time to
turn 90 degrees
4.8 knots 350 yards 2:21 minutes
7.3 knots 350 yards 1:30 minutes
11.7 knots 330 yards 1:00 minute
15.3 knots 380 yards 0:50 minute

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CHAPTER 4

THE TORPEDO FIRE CONTROL PARTY

400. GENERAL:

The Submarine Organization provides in its battle bill for the condition known as "Battle Stations Torpedo". This is an all hands evolution requiring specific stations for every member of the ship's complement. The ship's complement at "Battle Stations Torpedo" is divided into three groups: (a) The Fire Control Party, (b) the ship handling and maneuvering party, and, (c) the torpedo handling party. This chapter enumerates the members of the Fire Control Party and lists their primary duties. Their detailed duties and procedures are covered in Chapter VI.

401. APPROACH OFFICER:

The Approach Officer is the officer conducting the approach and the attack. Except in special training exercises he is the Commanding Officer of the submarine. His station is normally in the conning tower at the periscope. When a night attack on the surface is being conducted he may take station either in the conning tower or on the bridge.

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As the conning officer, he maneuvers the submarine into a position from which an attack can be delivered. He coordinates the activities of all members of the Fire Control Party and furnishes them the information needed to solve the torpedo fire control problem.

402. ATTACK AND SONAR COORDINATOR:

The Attack and Sonar Coordinator is usually the Executive Officer and is the number two member of the Fire Control Party. His station is in the conning tower. His primary duty is to be informed in detail regarding sonar conditions in order to direct and coordinate the efforts of all the Sonar Operators. His secondary duty is to assist the Approach Officer in coordinating the work of all members of the Fire Control Party.

403. TDC OPERATOR:

The TDC Operator is an officer whose station is in the conning tower at the position keeper section of the TDC. His primary duty is to operate the position keeper and, using all available information, obtain the most accurate values of target course, speed, and range that can be determined.

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404. ASSISTANT TDC OPERATOR:

The Assistant TDC Operator is an officer whose station is in the conning tower at the angle solver section of the TDC. He has two primary duties: (a) to assist the TDC Operator in obtaining the course and speed of the target, and (b) to insure that the proper gyro angle is set on each torpedo when it is fired.

405. NAVIGATIONAL PLOTTER:

The Navigational Plotter is an officer whose station is in the conning tower at the DRT. His primary duty is to maintain a navigational plot of the target or targets designated by the Approach Officer. He furnishes the TDC Operator and the Approach Officer the values of target course and speed obtained from the plot. In addition he furnishes predicted data regarding the target's position based on best known target course and speed, if requested.

406. PERISCOPE ASSISTANT:

The Periscope Assistant is an enlisted man, usually a quartermaster, whose station is at the periscope being used by the Approach Officer. His primary duty is to assist the Approach Officer as directed in his operation of the periscope.

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407. SONAR PLOTTER:

The Sonar Plotter is an officer whose station is in the control room. His primary duty is to obtain the course of the target from information furnished by sonar.

408. SONAR PLOT RECORDER:

The Sonar Plot Recorder is an enlisted man whose station is in the control room. His primary duty is to record the sonar bearings of the target as directed by the Sonar Plotter and assist him in obtaining the course of the target.

409. SONAR OPERATORS:

The Sonar Operators are enlisted men who are specially trained in the operation of sonic and supersonic sonar equipment. Their primary duties are to provide bearings end ranges of ships designated by the Sonar Coordinator in the manner and when directed by him. There are at present three sonar stations in a fleet or guppy submarine, as follows:

Sonar I - JT in forward torpedo room.
Sonar II - WFA or WCA in conning tower.
Sonar III - WFA or WCA in conning tower or in forward torpedo room.

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4.10. ST RADAR OPERATOR:

The ST Radar Operator is an enlisted man whose station is at the ST console in the conning tower. His primary duty is to furnish the Approach Officer and other members of the Fire Control Party the ranges of targets designated by the Approach Officer. He may also be directed by the Approach Officer to furnish approximate bearings.

4.11. FIRING KEY OPERATOR:

The Firing Key Operator is an enlisted man, usually a Fire Controlman, whose station is at the firing panel in the conning tower. His primary duties are to relay orders from the Approach Officer to the torpedo tubes and to fire the torpedoes when directed to do so.

412. GYRO ANGLE SETTERS:

The Gyro Angle Setters are enlisted men. They are stationed one in each torpedo room, at the gyro setting indicator regulators. Their primary duties are to see that the correct gyro angles are being set on the torpedo tubes as directed by the Assistant TDC Operator.

4.13. SS RADAR OPERATOR:

The SS Radar Operator is an enlisted man whose station is at the SS Radar Console in the conning tower. His primary duties are to provide the Approach Officer and other members of the Fire

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Control Party the bearing and range of targets designated by the Approach Officer.

414. SV RADAR OPERATOR:

The SV Operator is an enlisted man. He may be stationed at the SS console in the conning tower or the SV console in the control room depending upon the tactical situation. His primary duties are to provide ranges and bearings of aircraft or surface targets as directed by the Approach Officer.

415. TBT OPERATOR:

The TBT Operator is an officer whose station is at either the forward or after TBT on the bridge. His primary duty is to furnish the Fire Control Party bearings of the target and other information regarding the movements of the target or targets designated by the Approach Officer. This station is manned only during surface attack.

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CHAPTER 5

DUTIES OF THE FIRE CONTROL PARTY

500. THE APPROACH OFFICER

(a) The Periscope The periscope is the most important instrument at the command of the Approach Officer. It is by his use of the periscope that he is able to furnish the members of the Fire Control Party the information they need to compute and set the proper gyro angle on the torpedoes as they are fired. Let us, then, before discussing his duties, review briefly the salient features of the periscopes now in use and the techniques of their use.

(b) The two periscopes presently installed in fleet submarines are the type IV in the number one position and the type II in the number two position. Although these are alike in many respects the most outstanding difference is that the type IV contains a radar by means of which ranges may be obtained. The main characteristics of the two periscopes are as follows:

Type II Type IV
Magnification high power 6.0X 6.0X
Magnification low power 1.5X 1.5X
Maximum elevation of line of
sight (above horizontal)
74.5 degrees 45 degrees

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Type IIType IV
Maximum depression of
line of sight (below horizontal)
10 degrees 10 degrees
True field high power 8 degrees 8 degrees
True field low power 32 degrees 32 degrees
Ranging Device Stadimeter
Telemeter
Scale
Radar
Telemeter
Scale
Outer diameter reduced
section
1.414 in 3.75 in
Optical length 40 ft 36 ft

An examination of the above tables reveals that in order to obtain radar ranges we have had to sacrifice: (a) about six feet of periscope depth, (b) the ability to conduct a visual search above 45 degrees, and (c) 2.3 inches in the size of the tapered section of the tubs. These facts should be borne in mind when selecting the periscope to be used in different tactical situations.

The field of the periscope in low power (32 degrees) is four times the field in high power (8 degrees), but at the same time objects appear only 1/4 as big in low power as in high power with consequent reduction in detail. This can be clearly seen in Plate II.

Referring to Plate II we see that the reticule of the periscope has inscribed on it a series of vertical end horizontal lines. In low power each small division represents one degree while in high power each all division represents 1/4 degree. If the Approach

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Officer knows or can estimate the masthead height of the target in feet the number of horizontal divisions covered by the ship between its water line and masthead will be a measure of the range of the target. In the figure the target subtends 5 divisions in high power and 1 1/4 divisions in low power. It would obviously be impracticable to convert this value of angle to range at each periscope observation. The obvious solution is some form of precomputed graph or scale. We know that at a range of 1000 yards, 17 1/2 yards, or 52.5 feet will subtend an angle of 1 degree. Using this relation we can deduce the following formulas:

R(range) = (19.1 h / n)

R(range) = (76.2 h / N)

R = range in yards
h = height in feet
n number scale divisions low power
N number scale divisions hi power

Plate III is a picture of one type of scale ("range omnimeter") which may be constructed. In the figure the masthead height of the target is 100 feet. The arrow of the sliding scale is set opposite the masthead height and the range is read opposite the number of divisions. In this case 1550 yards is read opposite 5 divisions high power and 1 1/4 divisions low power. Ranges obtained in this manner are commonly referred to as "telemeter ranges". Estimates of

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ranges should be made to the nearest 1/8 division.

(c) The second method of obtaining ranges is by means of the stadimeter installed in the Type II periscope. The stadimeter relies for its operation upon the formation of two identical images which can, by means of a handwheel on the periscope, be vertically displaced with relation to each other. Normally the handwheel is at the limit of its counter-clockwise travel. To obtain a range, the handwheel is turned clockwise until the target masthead in one image coincides with the target waterline in the other image. The range is then read on the stadimeter scale opposite the appropriate masthead height. In Plate III, a picture of a stadimeter scale, a masthead height of 60 feet gives a range of 2300 yards. Note that the scale is constructed for high power observation. When ranges are measured in low power the computed value must be divided by four.

(d) The third method of obtaining ranges is by use of the radar installed in the Type IV periscope. In this method the range of the selected target is measured directly by the ST Radar Operator when the periscope is raised and trained on the target.

(e) Of the three methods the radar ranges are the most accurate and depend primarily upon the adjustment of the radar which is usually plus or minus 35 yards. The accuracy of telemeter or stadimeter

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ranges depend first, upon the skill of the observer and second, upon the accuracy of the estimate of target masthead height.

(f) The value of the masthead height of the target may be obtained by intelligence, estimate, or by a method referred to as "radar stadimeter" (telemeter) estimate. The latter of course is the most accurate and is accomplished as follows; assuming that the target has been tracked using the ST periscope, the Type II periscope is raised immediately following an ST periscope observation, a stadimeter range observation is made as described above, but instead of reading range on the scale, the masthead height is read opposite the value of the TDC generated range.

(g) When radar ranges cannot be obtained the Approach Officer must rely upon his ability to correctly estimate the height of the funnel or masthead, or other prominent mark on the ship's structure above the water line. If the target ship can be properly identified an accurate value may be obtained from intelligence information supplied the ship. If this is not available the following procedure will he of assistance:

(1) Count or estimate the number of decks that are seen above the main deck.

(2) Add to this figure the approximate number of deck heights equal to the observed freeboard.

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(3) Multiply the total by eight to determine the height of the top of the bridge structure above the visible waterline.

(4) Using height of bridge structure above the visible waterline as a yardstick, approximate the masthead height. The masthead heights of merchant ships are on the average about 2.1 times the bridge height (above waterline). A masthead height which appears to be shorter than normal will be about 1.7 to 1.8 times the bridge height, while one which appears to be higher than normal is approximately 2.2 to 23 times the bridge height.

(5) Funnel heights may be estimated by approximating the number of deck heights of the funnel which is seen above the top of the bridge structure and adding this height to the bridge structure height.

(6) At extreme ranges it must be remembered that the waterline is below the horizon. This necessitates estimating the position of the waterline.

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(h) The following points should be kept in mind in height determination:

(1) Masthead heights may be purposely altered by the enemy to cause inaccuracies in periscope ranges.

(2) Tops of masts may be camouflaged in such a manner as to be invisible under average visibility conditions at any except short ranges.

(3) Funnel height is normally sufficient to insure that the smoke which is blown in the direction of the bridge by a tail wind will pass well over the bridge.

(4) Coal burners require taller funnels to insure adequate draft.

(5) Funnels of modern vessels having forced draft do not require as tall a funnel as older vessels without forced draft.

(6) Diesel propelled ships require no draft. Funnels are normally short, are not required, and generally have such dimensions as to provide a good appearance on the ship.

Regardless of the methods employed by the individual Approach Officer, skill in estimating masthead heights, and ability to obtain accurate ranges can

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be acquired and maintain only by constant practice. Even when radar ranges are available daring an approach the Approach Officer should also obtain telemeter ranges as a means of improving and maintaining his skill.

501. TARGET LENGTH

(a) The length of the target may be obtained by estimate based on intelligence, by observation with the horizontal telemeter scale, or by observation with the stadimeter. As in estimating masthead height accurate identification of the target make it possible to obtain its length from available intelligence information. There is, however, no yardstick which may be used as a guide.

(b) When the length is to be obtained from a telemeter observation the number of divisions subtended by the target on the horizontal scale is measured in the same manner as when obtaining ranges. In Plate II the target subtends about 12 divisions in high power and therefore 3 divisions in low power. Since we see a foreshortened length of the target we must correct the computed length for angle on the bow. The horizontal and vertical telemeter scale are identical so we may set up the following relation:

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L (length) = R n / 19.1 SinAb

L (length) = R N / 76.2 SinAb

R = Range in yards
n = Number scale divisions in low power
N = Number scale divisions hi power
Ab = Angle on the bow

(c) Since these formulas are identical with the ones for obtaining range except that L is substituted for h and the value sin Ab added we may obtain the value of the foreshortened length by setting the number of scale divisions opposite the radar, observed, or TDC generated range and read the foreshortened length opposite the arrow on the masthead height scale. We now need to correct this value for angle on the bow. Plate V shows the scale set for the conditions shown in Plate II assuming an angle on the bow of 40 degrees. Note that in this case the number of telemeter divisions, 12 high power or 3 low power, is set opposite 1/2 the range, 920 yards. This is done because the masthead scale does not go above 200 feet. The foreshortened target length is then 290 feet or twice the value read opposite the arrow. On the second sliding scale the angle on the bow 400 is set opposite the target length 290 feet and opposite the arrow at 90 degrees we read 450 foot the full target length.

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(d) A simple variation of the telemeter principle is to determine the target length in degrees from the telemeter scale (one large division equals 1 degree in high power; one small division equals 1 degree in low power). Since 1 degree subtends 17.5 yards or 52.5 feet at 1000 yards, we may round this off and say that 1 degree subtends 50 feet at 1000 yards. Therefore, the following formula can be used with acceptable accuracy:

Target Length No. degrees subtended X 50 ft X
(Range in 1000's yards) / (Sin Ab)

Just as is true in ranging with the periscope the accuracy of the target length determined depends upon the skill of the Approach Officer.

502. PERISCOPE TECHNIQUE

(a) Good periscope technique may be simply defined as the ability to obtain the maximum amount of accurate information, with the minimum length exposed, in the minimum time. The Fire Control Party is directly dependent upon information obtained from periscope observations for a correct solution of the problem. For this reason Approach Officers should devote thought and time to the perfection of their periscope technique to insure that they are able to provide the Fire Control Party all the

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information it requires. Visual acuity is the first requisite of a good periscope observer. This does not mean that the observer must have perfect vision since the periscope optics can compensate for minor deficiencies in vision. It does mean, however, that the observer must see what he is looking at and is able to describe accurately, after the periscope is lowered, the picture presented to him when the periscope was raised. To acquire this skill constant practice is required. One way to accomplish this is to reconstruct in the minds' eye after each periscope observation, whether during an attack or not, the picture seen through the periscope. Try to include in the picture all possible details.

(b) There are no set rules which can be laid down which will apply under all conditions. The following, if followed, however, should be of assistance:

(1) Make enough observations during the early phases of the approach to insure an early target speed solution.

(2) During the later stages of the approach and during the attack observations should be required only to maintain a correct target course solution.

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(3) The likelihood of detection depends more upon amount and length of periscope exposure than upon the diameter of the periscope head or the number of looks.

(4) The optimum exposure time for an ST periscope is 5 seconds, for other types 10 seconds.

(5) Have the periscope in low power when it breaks water. This insures maximum field of vision and helps to locate the target.

(6) To avoid mistaking low power for high power observation acquire the habit of having right wrist bent over the periscope when periscope is in low power. When the wrist is in a normal arid comfortable position the periscope will then be in high power.

(7) Change depth as necessary to insure that only the minimum amount of periscope required for the observation is exposed.

(8) Make observations only at 1/3 speed when within 6000 yards unless tactical situation demands otherwise.

(9) When making high speeds at long

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ranges, where air cover is not present, do not deny the Fire Control Party information to maintain speed. A quick observation should not be detected.

(10) When making an observation examine the target group first give the target bearing and then lower the periscope. In this manner the periscope will be on the bearing of the target when it is lowered. Though this may appear to be a minor item it will eliminate a source of confusion and greatly assist the Fire Control Party.

(11) Do not describe the situation while the periscope is exposed. This serves no useful purpose and prolongs the observation.

(12) Have the periscope in low power during firing. The target bearing is just as accurate, while the increased field will often permit observation of close escorts which would not be visible were the periscope in high power.

503. PERISCOPE PROCEDURE

The procedure employed in all periscope observations

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is essentially the same. However, since the range may be obtained in three different ways there are slight variations in the procedure depending on how the range is to be obtained. For purposes of clarity the complete procedure for each type of observation will be given:

(a) ST Periscope Observation
Approach Officer Standby for observation
TDC Operator Bearing (range and angle on the bow, if desired)
Approach Officer Up periscope
Periscope Assistant Raises periscope and places it on the bearing announced by the TDC Operator
ST Radar Operator When periscope breaks water announces PIP or NO PIP
Approach officer Bearing ____ Mark! Down Scope
Periscope Assistant On bearing _____ Mark! rings the bearing buzzer or if the bearing transmitter is out of order, announces the bearing. Lowers the periscope.
ST Radar Operator Obtains range and immediately following the bearing buzzer rings the range buzzer
Approach Officer Angle on the bow _____ or target has zigged angle on the bow ____or target is zigging to his right (left)
TDC Operator Generating ____ or indicates a zig of ____ degrees

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(b) Stadimeter Observation
Approach Officer Standby for observation
TDC Operator Bearing ____ (angle on the bow, if desired)
Approach Officer Up Periscope
Periscope Assistant Raises periscope and places it on the bearing announced by the TDC Operator
Approach Officer Bearing ____ mark!
Periscope Assistant Rings the bearing buzzer or if transmitter is out announces the bearing
Approach Officer Range ___ mark! (Masthead ____feet). The Approach Officer may announce a masthead height should he desire to use a value different from that previously decided upon.
Periscope Assistant Range ______ .
Approach Officer Down scope. Angle on the bow ____ or (see ST observation.
TDC Operator Generating or indicates a zig of _____ or indicates a zig of _____ degrees.

(c) Telemeter Observation
Approach Officer Standby for observation
TDC Operator Bearing _____ (angle on the bow, it desired)
Approach Officer Up periscope
Periscope Assistant Raises periscope and places it on the bearing announced by the TDC Operator
Approach Officer Bearing Mark!

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Periscope Assistant Rings the bearing buzzer or if transmitter is out announces the bearing
Approach Officer RANGE MARK, DOWN SCOPE, Range ____ Divisions ____ Angle on the bow ____ or (see ST observation)
Periscope Assistant Range yards. This value of range is obtained from the range omnimeter. Some Approach Officers prefer to operate the range omnimeter themselves. Either procedure is acceptable.
TDC Operator Generating _____ or Indicates a zig of ____ degrees

NOTE: Regardless of type of observation the Approach Officer, at the initial observation, should not give the order DOWN PERISCOPE until the TDC Operator has announced MATCHED, Procedure may require TDC Operator to announce own speed on STANDBY FOR OBSERVATION when It exceeds 3 knots should the Approach Officer desire.

(d) Since the accuracy of the ranges is variable when using the stadimeter or telemeter the Approach Officer should inform the Fire Control Party when he considers the range accurate or doubtful. When approaching the firing point the phrase "FINAL OBSERVATION" should never be used. It has no special significance and will almost invariably confuse the Fire Control Party.

504. DUTIES

The duties or the Approach Officer are to:

(A) Make periscope observations and to provide

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to members of the Fire Control Party such information as they require regarding the target or targets to be attacked.

(B) Plan the attack and inform the members of the Fire Control Party in detail regarding his intentions.

(C) Issue all necessary orders to insure that the torpedoes will be ready to fire and will be fired in the manner he has planned.

(D) Conn the ship to a position from which a successful attack may be delivered.

(E) Coordinate the activities of all members of the Fire Control Party.

505. PERISCOPE OBSERVATIONS

At the initial observation following contact with the target the Approach Officer should furnish the Fin Control Party all details which are available to him at that time regarding the number and type of ships in the target groups This information should be sufficiently detailed to make it possible to identify the target in available intelligence publications so that an estimate of the target masthead height, length, and major characteristics may be available. He should furnish the Fire Control Party a careful description of the disposition of the target group, the approximate location and activity of air cover and screens if present. If time is available a rough sketch and out

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line of the disposition will prove helpful to the Fire Control Party. Any subsequent change in the disposition that is observed should be given to the Fire Control Party to insure that they remain properly oriented and able to interpret maneuvers and orders from the Approach Officer. He should insure that the ST Radar Operator understands the disposition and should assist him in identifying on the radar screen the target which is to be tracked. As soon as the target presents a favorably large angle on the bow an observation for target length should be made. At each observation of the target the Approach Officer should inform the Firs Control Party of his estimate of the target's angle m the bow. Since the observed angle on the bow and that obtained by Plot and TDC will frequently differ, he should be meticulous to insure that they know which value of angle on the bow he desires them to use. If the approach is being made by ST radar the masthead height of the target should be obtained a soon as practical so that it will be available in case the radar tails or it is necessary to shift to another periscope.

Although it is not possible to determine target speed merely by observation, general information indicating whether the target appears to be making high, or low speed will be helpful to the Fire Control Party. During

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the early stages of the approach the Approach Officer should attempt to make sufficient periscope observations to enable the Plot and TDC Operator to obtain an accurate solution of target speed before the range to the target becomes less than 6000 yards. The Approach Officer should keep himself informed of the speed solution obtained by Plot and TIC and in cases where differences exist direct the TDC Operator what value of target speed is to be used.

The Approach Officer will err more times in not providing his Fire Control Party with sufficient information than he will in giving them too much information. In training himself he should endeavor to conduct his approach in such a manner that the members of the Fire Control Party will not have to request from him any information which he has not already given to them.

506. PLAN OF ATTACK

(a) As early In the approach as possible the Approach Officer should inform his Fire Control Party of the target or target be to be attacked, whether the attack is to be made upon a single target, whether it is to be divided fire from a single tube nest against 2 or more targets, or whether he is to fire both the bow and the stern tubes. he should inform the Fire Control Party of the number of torpedoes to be fired at the target or targets, the depth and speed setting to be

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used on the torpedoes, the type and amount of spread he desires to use. When this information is provided to the Fire Control Party well in advance of firing they can plan their actions accordingly and be ready at the firing point to commence shooting and conduct the attack with the minimum of confusion. To wait until the firing point is reached or during the firing of one nest to inform the Fire Control Party that it is the Approach Officer's intention to also fire the other nest causes needless confusion.

(b) He should inform the Torpedo Rooms of the firing order of the torpedoes. When a full load of one type torpedo is being carried on board the order in which the tubes are fired is not or great importance, If, however, a mixed load of torpedoes is being carried a definite tube firms order is the Approach Officer's only insurance that the torpedoes fired are the ones he planned to fire. For this reason it is good training to indoctrinate the Fire Control Party and the Torpedo Rooms to expect the designation of a firing order.

(c) The Approach Officer should direct that the tubes be flooded before it may be necessary to rely on sonar information so that the sonar equipment will not be blocked out at a critical time by the noise which occurs when the tubes are flooded.

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Since there is no pressure upon the torpedoes themselves until the outer doors are opened it should be possible to flood the tubes well in advance. Under combat conditions it is good practice to flood all tubes which can be fired even though it is not intended to use them, since unexpected changes in tactical situation may make it desirable to fire more torpedoes than had been formerly planned. When the critical range is reached the outer doors of all flooded torpedo tubes should be opened.

(d) There are various methods of firing. These are described in detail in Chapter 7. It is extremely important that all members or the Fire Control Party know which method of firing the Approach Officer intends to use and that he train himself and the Fire Control Party until they are proficient as a team in the selected method. Much confusion will occur at the firing point if the Fire Control Party is not thoroughly drilled in this phase of the attack. All the work and the risk involved in a careful approach and attack is wasted if errors are introduced in the TDC at the moment of firing.

507. SHIP HANDLING:

The Approach Officer issues all orders to the helm, all changes in depth and attitude of the submarine. It is advisable for an inexperienced Approach Officer to make a conscious effort to check off in his own mind prior to an observation the actual depth of a submarine, the

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angle on the boat, the indicated ship's speed, the position of the rudder and the annunciators, and the ship's head. The conduct of this check-off list will eventually become a matter of habit but attention by an inexperienced Approach Officer to the above will avoid many embarrassing situations.

508. COORDINATION OF FIRE CONTROL PARTY:

All members of the Fire Control Party rely upon the Approach Officer for information and for decisions during the course of an approach. In a well coordinated Fire Control Part: there is never any doubt in the minds of the individual members as to what is expected of them at any given time and under any given conditions. This situation cannot be arrived at over night or by any "quick and easy method". It will exist only if the Approach Officer devotes much thought and time to self training and the establishment of set phraseology and procedures which are carefully followed and meticulously adhered to.

509. BLANK

510. THE ATTACK AND SONAR COORDINATOR:

(a) The aided emphasis that has been placed upon sonar by new developments in anti-submarine warfare and the use of submarines is anti-submarine warfare ships have brought to light many deficiencies in our present submarine sonar equipment and the need for increased efficiency in obtaining and processing available sonar information. In the past the executive officer has been

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designated the Assistant Approach Officer. As Assistant Approach Officer his duties in an efficient Fire Control Party have been nominal. Since, next to the commanding officer, he is the most experienced officer on board a submarine, it is proposed to utilize his talents in the solution of the sonar problem.

(b) As the Sonar Coordinator of a submarine his duties should include the supervision and training or the Sonar Operators according to sane planned schedule with the end that he should be intimately acquainted with their capabilities and limitations. He should be charged with the development of set operating procedures and the indoctrination of the Fire Control Party in standard sonar phraseology and orders.

(c) During torpedo attacks and torpedo evasion he should integrate the Sonar Operators into the Fire Control Party and supervise their operations. He should see that the best available sonar bearings are being supplied the TDC, designate to the various sonar operators the targets which they are to track and assist them with additional information from time to time to insure that they do not become confused and track the wrong targets. He should supervise the tracking of the sonar plotting party and see that they are supplied with the information necessary to properly fulfill their mission as members of the Fire Control Party.

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(d) During sonar attacks he should coordinate the activities of the Sonar Plot, the Nav Plot and the TDC to obtain the most accurate possible analysis of the target's movement.

(e) He should be familiar with the sonar conditions existing during the approach, such as the optimum listening range of the day, the optimum range of the day, the location of layers and the optimum evasion depth so that he may properly advise the Captain and furnish him this information when desired.

(f) As the attack coordinator he should be alert to remind the Approach Officer when routine orders and procedures have been inadvertently neglected and assist the approach officer in any other manner he may desire.

511 - 519. BLANK

520. THE TDC OPERATOR:

(a) Details of Operation

The details of the operation of the TDC are discussed in OP1442A. The information presented here will consist only of the duties of the TOC operator as a member of the Fire Control Party.

(b) Manning the TDC

1. Check to see the proper power and own ship's inputs (course and speed) are available and being received correctly.

2. Check timer reset to zero and start the problem upon the order of the Approach Officer or Other designated. officer. Also check to see that the TDC timer is synchronized

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with Plot's timer.

(c) Initial Speed Setting

1. At the beginning of the problem set target speed to a value obtained from the Approach Officer or to a value determined by experience. In lieu of a better estimate an initial analyzing speed of 15 knots, which is a good. average speed determination is to be used.

2. If radar tracking is being conducted set target speed on the value determined by Plot, or to zero if the speed zero method of speed determination is to be used.

(d) Initial Observation Procedure

1. See chapter 5, para. 503, Periscope Procedure.

2a. Match the observed values in the receiver section of the TDC for an ST observation.

b. Enter the observed values as announced by the respective members of the Fire Control Party for a stadimeter or telemeter observation.

3. When the observed values are set in the TDC report "MATCHED".

(e) Successive Observation Procedure

1. See chapter 5, para. 503, Periscope Procedure.

2. On the order "STANDBY FOR OBSERVATION", announce the generated target relative bearing, own ship's speed (if desired), angle on the bow (if desired) and the generated range (except for stadimeter and telemeter observations).

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3a. For an ST observation read and announce the bearing and range corrections, and match the observed values in the receiver section of the TDC.

b. For a stadimeter or telemeter observation read and announce the bearing correction and match the observed value in the receiver section of the TDC. When the Assistant TDC Operator has computed the range correction, enter the correction in the TDC.

4. After the periscope has been lowered the TDC Operator carries out the angle on the bow procedure which follows:

a. If the observed angle on the bow is within 10 degrees of the generated value announce GENERATING _____, and reset or leave the angle on the bow as directed by the Approach Officer.

b. If the observed angle on the bow is not within 10 degrees of the generated value announce INDICATES A ZIG OF ____ DEGREES, and set the angle on the bow called by the Approach Officer.

c. if the Approach Officer reports THE TARGET HAS ZIGGED TO HIS RIGHT (LEFT), ANGLE ON THE BOW IS ____ set the new angle on the bow.

d. If the Approach Officer reports THE TARGET IS ZIGGING TO HIS RIGHT (LEFT), zig the target 30 degrees in the indicated direction and await further observation of the angle on the bow to adjust the TDC.

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e. If the Approach Officer reports NO CHANGE, announce the generated angle on the bow.

(f) Speed Determination

The TDC Operator must coordinate the determination of target speed through his own analysis and that of the Assistant TDC Operator and Plot. After the angle on the bow has been set on each observation the TDC Operator must mentally calculate the speed and angle on the bow. This he must do primarily to act as a check against mistakes made by the Assistant TDC Operator. Methods of mental calculation are discussed in OP1442A. When the solutions for target course and speed by the TDC Operator, the Assistant TDC Operator, and Plot are not in close agreement the Approach Officer should be so informed. During firing the TDC Operator must maintain a close check on the target data in conjunction with Plot. Any pronounced deviations in target data should be announced to the Approach Officer. It is to be emphasized that Plot and Assistant TDC Operator are aids to the TDC Operator and the responsibility for correct target course and speed rests upon the TDC Operator.

(g) Radical Changes in Range

Similar to the angle on the bow procedure, radical changes in range should be brought to the attention of the Approach Officer prior to entering in the TDC.

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(h) Utilization of Sonar Data

Between periscope observations in the approach phase the TDC Operator should evaluate the TDC solution with the sonar information available. Particularly, zig indications and angle on the bow errors should be announced. In the attack phase and in pure sonar attacks the TDC Operator should keep the generated TDC target relative bearing matched with the sonar bearings. At all, times the target length dial should be properly set in order to keep the generated target star bearing corrected.

(i) Critical Range

When a target speed has been obtained it should be announced with the critical range. As the target, speed changes in the solution the new speed and critical range should be announced.

(j) Supplying the Approach Officer Information

Since the Approach Officer often does not have satisfactory access to the position keeper section of the TDC, the TDC Operator must provide him with same or all of the following:

1. Generated range.

2. Generated Angle on the bow.

3. Generated bearing.

4. Distance to the track.

5. Present ship's track angle.

6. Courses to come to for various ship track angler and lead angles.

7. Torpedo track angle.

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8. Torpedo course,

9. Direction, amount and tendency of gyro angles.

10. Torpedo run.

11. Target course and speed.

12. Critical range.

13. Problem time,

14. Time since last zig.

15. Time since last observation,

16. Range rate.

17. Bearing rate.

(k) Masthead Height Check

The TDC Operator should announce the generated range when the Approach Officer orders STANDBY FOR MASTHEAD HEIGHT CHECK. See chapter 5, Approach Officer, Masthead Height.

(1) Firing Point Procedure

1. See chapter 7, Firing Methods,

2. At the order BEARING MARK match the observed values of bearing and range (ST observation). For stadimeter and telemeter observations at the Firing point only the bearing is matched.

3. Announce SET.

4. On subsequent check bearings announce SET after the observed values are matched.

521 - 529. BLANK

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530. THE ASSISTANT TDC OPERATOR:

The detailed duties of the Assistant TDC Operator are discussed in OP 1442A. The information presented here will consist of the duties of the Assistant in relation to the Fire Control Party.

531. MANNING THE ASSISTANT TDC STATION:

The Assistant will man the Assistant TDC station and put on the JA head phones. This circuit has the Forward and After gyro setting indicator regulator operators on it. The Assistant should make a communication check with the respective GSIR Operators. He should check the TDC Gyro Angle Indicating and Regulating switches in the OFF position.

532. ANALYZING:

Using the standard analyzation form the Assistant TDC Operator makes a comparison between the generated and observed values and computes speed and angle on the bow. This information is given to the TDC Operator for use in the TDC. The Assistant should keep the PDC Operator advised of each new computed speed and from his computations advise the Approach Officer of the computed angle on the bow.

The methods of analyzing are described in Mk. 4 TDC Operating Procedure .

533. GYRO ANGLE ORDER CHECK:

At approximately the critical range the Assistant should stop analyzing. At this time he should be able to determine whether it will be a bow or stern tube shot and he should use, the following procedure in engaging the Gyro Setting Indicator Regulator.

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If he is not certain of the tube nest to be used he should cut in both the Forward and After GSIR's.

Assistant TDC OperatorGyro Setter
A. If gyros are less than 150 degrees Gyros forward or aft match Gyros in automatic. Turn switch to IND-REG position. A. When gyros match and settle down, report TDC Gyros Forward (or Aft) matched in automatic.
B. Gyros Forward or Aft Standby for Gyro check. B. Gyros Forward (or Aft) Standing By.
C. Standby - Mark! C. Reads gyro angle order to the closest 10' and reports.
D. Check.

If the gyro angle order does not check within 10' the above procedure should be repeated. If it does not check again the transmission should be checked by the Fire Controlman if time permits. If time is not available it will be necessary to set gyros by hand.

534. SPREAD COMPUTATION:

The Approach Officer will give the Assistant TDC Operator the following information as soon as it is available:

a. Type of spread to use.

b. Target length.

c. Number of torpedoes to be fired.

d. Percent coverage to be used.

The Assistant TDC Operator should compute the spread in accordance with chapter 6.

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535. FIRING POINT PROCEDURE:

At the firing point, after the TDC Operator announces SET for the first torpedo, the Assistant TDC Operator announces SHOOT, if he has the correct spread set in the TDC and the correct solution light is on. The Assistant TDC Operator then waits for a period of five seconds or until he is sure that the torpedo has left the tube and he repeats the above procedure for the remaining torpedoes. If there is no check bearing between successive torpedoes he announces SHOOT when the above conditions are met, namely spread set, correct solution light on, and he is certain that the preceding torpedo has left the tube.

536-539 BLANK.

540. THE NAVIGATION PLOTTER:

The Navigational Plot is one of the most important stations in the submarine fire control party. It is the only source from which a picture of the entire approach can be obtained. The Navigational Plot furnishes valuable information on target speed, target course, times of target zigs, average length of zig legs, and predicted target range when the submarine is below periscope depth. In order to furnish the Fire Control Party with this valuable information the Navigational Plotter must strive for accuracy, neatness, and speed. This may be accomplished only with

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the knowledge of the proper symbols, proper use of the plotting instruments, and continuous practice.

The most important tools of the Navigational Plotter are the Dead Reckoning Tracer (DRT), the Parallel Motion Protractor (PMP), the Bearing and Range Indicator, and speed scales or speed dividers. Before describing the plotter in action let us consider the proper use of these instruments.

541. DEAD RECKONING TRACER (DRT)

The Dead Reckoning Tracer on submarines is a glass topped table with a light "bug" under the glass. The "bug" with its projected spot of light indicates own ship's position at any time from inputs supplied by the ship's gyro and underwater log. Two switches on the point of the table energize the North-South, East West component motors. The scale of the "bug" travel is determined by the scale setting device. This device may be set on 500 yd/in., 1000 yd/in., and 1-8 mi/in. (Later modifications also have 200 yd/in.), The 1-8 mi/in, scale has an additional scale for selection of scales between 1-8 miles/in. The scale of 1000 yd/in. Is normally used for submerged approach plotting and the DRT table should be set up on this scale for normal cruising. The "Bug" on the DRT is moved to any position by two handwheels located on the front of the table.

The Parallel Motion Projector is normally used in

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conjunction with the DRT and must be oriented to the movement of the DRT "bug". Orientation can be accomplished by performing the following operations in sequence.

(a) Mark DRT "bug" position on the top plotting surface.

(b) Disengage the scale setting clutch and move DRT "bug" 6-8 inches in a 090 direction and plot new "bug" position.

(c) Position the protractor arm along the two points and adjust the bearing indicator of the protractor so that the 090-270 true bearing line is indicated.

(d) if desired, orientation to the 000-180 line may be accomplished in a similar manner.

(e) A somewhat less accurate orientation can be effected by positioning the protractor along the front edge of the table and adjusting the indicator in a 090-270 direction.

542. THE PARALLEL NOTION PROTRACTOR (PMP)

The Parallel Motion Protractor, sometimes called a drafting machine, is a protractor cammed by a parallel-motion linkage which is fastened to the upper edge of the DRT table. The linkage permits the movement of the protractor to any part of the table with out loss of orientation. The graduated protractor rim

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or compass rose can be clamped as desired, and hence oriented to coincide with the North-South direction of the table. Two recommended methods of using the Parallel Motion Protractor will be discussed, either of which or a combination of which may be used in the cramped space of the submarine plotting station:

(a) Direct Plotting:

1. Plot position of own ship at time bearing and range is taken.

2. With the range ruler free to rotate, set ruler at proper bearing.

3. Place the bearing indication arrow that points toward the ruler on desired bearing, then lock the ruler.

4. Place the zero mark of the ruler exactly on the desired marked position along own ships track. The edge of the ruler now extends along the true bearing line from own ship's position.

5. Read outward from zero to the desired range, draw about a one-inch bearing line and mark the point.

6. immediately after establishing this point, release lock on ruler leaving it ready for use in plotting angle on the bow.

(b) Indirect Plotting:

Indirect plotting makes use or the reciprocal

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bearing mark to facilitate the plotting of targets which are awkward to handle by direct plotting. The following are variations from direct plotting:

1. The desired bearing is read beside the arrow which is 180 degree from the rule side of the PMP arm.

2. The desired range instead of the zero mark is placed at the marked position on own ship's track.

3. The target's position is then plotted at the zero mark on the ruler.

543. THE BEARING AND RANGE INDICATOR:

The Bearing and Range Indicator is the source from which the plotter gets the information to Plot. He must insure that the proper selector switches are energized for the stations from which he is to receive his information. The Bearing and Range Indicator indicates True Bearing and Range in thousands of yards.

544. SPEED SCALES OR DIVIDERS:

There are numerous aids for the plotter for converting distance run in a length of time to target speed. Rulers properly calibrated are issued by BuShips. Curves and tables may be made up by the individual plotter, or speed dividers may be obtained. The individual Navigational Plotter must try them all and select the one which he considers best for his own use.

There are three types of plot that the Navigational

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Plotter must be able to handle with great facility: (1) The Periscope Radar Plot; (2) The Stadimeter Plot; and (3) The Radar Plot. These will be taken up in detail below, there are, however, four things common to all of these plots which the Navigational Plotter must accomplish before beginning his plot. Upon manning battle stations the Navigational Plotter must:
a. Orient the Parallel Motion Plotter - with the DRT "bug".

b. Select the proper plotting scale.

c. Place "bug" across the table from the target true bearing to give him the maximum of plotting surface.

d. Turn on DRT table and check "bug" moving properly with respect to own course and speed.

545. THE PERISCOPE RADAR PLOT (Refer to Plate VI):

The Periscope Radar plot is made from optical bearings and radar ranges. This information is the most accurate that can be obtained on a submarine. Since the information is accurate the plot is easy to make and analyze. Referring to Plate VI we will trace the plot out point by point and see what information was obtained by the plotter and how he obtained it.

At problem time 0:15 an observation is taken. The Plotter records on a convenient place on his plot the time, true bearing, range and angle on the bow. He then plots this observation, drawing the angle on the bow relative to the bearing line. Since this is the initial observation the plotter has no intonation to

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furnish after plotting the point. At time 3:15 an observation is taken and plotted. The plotter now has two plotted points and will give the following information to the approach officer: target course 110, target speed 15, angle on the bow overestimated by 10 degrees. The plotter then labels his plot placing the leg course and speed in a box adjacent to the course line. He should then DR the target ahead along the target's course line to keep the picture up to date. At time 6:30 an observation is taken and the approach officer announces the target has zigged. The plotter plots the point and now has gore information to give the approach officer.

(a) Target Speed - The plotter finds the leg speed to be 17; this is not, however, the speed he gives to the Approach Officer. He goes beck to time 0:15 and from there measures the speed made good along the targets courses to time 6:30. This speed, called the overall speed, he finds to be 15 1/2 and announces it.

(b) Target course - Since the new target course at this time is merely that estimated by the Approach Officer's angle on the bow, the plotter does not announce a new course at this time.

(c) Zig time - To find the first estimate of zig time the plotter extends the angle on the bow line back to the intersect with the target's old course line. This intersects at the four minute DR. The plotter

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announces "zig time 4 minutes". This first estimate will only be as accurate as the Approach Officer's angle on the bow. The plotter then labels his plot placing the zig time in a box at time 4 and the overall speed 15 1/2 in a box adjacent to the time 6:30 point.

At time 8:00 an observation was plotted and the plotter announces the following information:

Target Speed: OVERALL TARGET SPEED 15 1/2
Target Course: NEW COURSE 150
Angle on the Bow: ANGLE ON TIME BOW OVERESTIMATED BY 20 degrees
Zips Tie: CORRECTED ZIG TIP 5 MINUTES

This corrected zig time was found by running the target's new course line and back to the old course line and taking the thee at the point of intersection.

Immediately after this observation the Approach Officer had to go below periscope depth. The plotter by making a DR track of the target is able to give the Approach Officer the present range at any time until the target zigs. At time 10:00 the Approach Officer asked for the range. The plotter calls out RANGE ____; the DR range at that time.

546. STADIMETER PLOT:

The source of information for the stadimeter plot is the periscopes Optical bearings, and stadimeter ranges are supplied by the Approach Officer together with his estimate of angle on the bow. Since the errors in stadimeter ranges may be great and variable the plot is much harder to make and analyze than the

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periscope radar plot.

A system of fairing in the target's course through the observed points must be used. The plotter must lean heavily on the Approach Officer's angle on the bow in arriving at the proper course line. In general the smaller angles on the how and the shorter ranges will he the most accurate. This must be taken into account when fairing in the target's course line. Overall target speed is, always, used in this type plot. The overall speed is taken along the faired in course line from the first bearing line to the last.

Zig time is computed in the same way as for the periscope radar plot. First estimate is obtained using the Approach Officer's angle on the bow. When new faired in course line is constructed a better estimate should be found. Plate VII is a typical stadimeter plot.

517. THE RADAR PLOT

The source of information for the radar plot is either the surface search or aircraft search radar. The information may be received with any frequency desired by the plotter. Since a great number of points may be plotted in a short time a very good course and speed may be determined quickly. Since no angle on the bow is received the target's course is wholly dependent upon the accuracy of the plotter. The plotter should select a time interval between

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observations that suits his plotting speed, usually one a minute, although once every half minute may be used if desired. With a definite time interval between observations the computation of target speed is simple. Since 1 knot equals 100 yards per 3 minutes the target speed in three minutes may be found by merely dropping the last two places of the number of yards the target traveled in that time. Speed in knots for 1 1/2 minutes time would be twice the number of yards divided by 100, etc. This is a very useful rule and may be used very readily when a constant time interval is used in plotting.

The points in a radar plot are plotted in the same manner as the other plots. Since there will be many more points a solid bearing line from own ship through the target position should be plotted every fourth or fifth observation to keep the plot oriented. Plate VIII is a sample radar plot.

548. THE NAVIGATIONAL SONAR PLOT

When the approach is being made with the aid of sonar bearings only the Navigational Plot can still furnish much valuable information to the TDC. Using a known or assumed speed the Navigational Plotter can fit this speed in between bearing lines and furnish TDC with reasonably accurate courses and ranges. This type plot is particularly valuable when the entire approach is made on sonar information only.

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The principles used in the sonar Navigational Plot are illustrated by Case IX, Maneuvering Board Manual, H.0. 217.

549. BLANK

550. PERISCOPE ASSISTANT:

The duties of the Periscope Assistant are as follows:

1. Raises and lowers the periscope in use on orders from the Approach Officer.

2. When the periscope is raised places it on the bearing designated by the TDC Operator.

3. Announces the relative bearing on the order BEARING MARK from the Approach Officer, when required, or rings the bearing buzzer.

4. Reads and announces the stadimeter range on the order RANGE MARK from the Approach Officer or operates the range omnimeter if telemeter ranges are being used. Computes the target length with the range omnimeter when required.

5. When the Approach Officer is observing the target group informs him when the keel depth of the submarine varies 1 foot or more from the ordered depth.

551 - 559 BLANK

560. THE SONAR PLOTTER:

The Sonar Plotter is a relatively new member of the Submarine Fire Control Party. His primary duty

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is to determine true target course from sonar bearings. This is accomplished by plotting bearings received from sonar by one of the plotting methods in use to determine the relative course of the target. The true course or the target is then obtained by combining relative course or the target, the actual or estimated speed of the target, and the submarine course and speed on a maneuvering board.

There are as yet no computers available to accomplish this and the Sonar Plotter must resort, therefore, to manual plotting. There are in use at present two methods of accomplish this; the Bearing Rate Plot and the Bearing Difference Plot.

561. BEARING RATE PLOT

As was explained under the duties of the Navigational Plotter we usually plot true bearing and ranges to determine the target's true course. If this is done on a maneuvering board we get target relative course and speed.

Now if we substitute for actual range a relative or abstract range we will get the direction of the relative movement line of the target (or relative target course). It can be proved mathematically that:

r = square root (K / (db/dt))

It is obvious that it would not be practicable to

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actually compute the various values of relative range during an approach. We can, however, assume a convenient value for K which is a constant and construct on a large maneuvering board a graph on which we can plot values of rate of change of bearing (db/dt) against true target bearing. Plate IX is a picture of such a plotting sheet in which K = 200

Plate X is a set of data which has been recorded by the Sonar Plot Recorder. The numbered lines are the actual sonar bearing of the target at 30 second intervals. The data which are plotted by the sonar plotter are the differences between bearings one minute apart and the mid-bearing from the recorder sheets For example, the first db/dt is 2 1/4 degrees plotted at true bearing 330 1/2 degrees. The mid-bearing from the recorder sheet say not be the exact mathematical mean of the two bearings but it is close enough for practical application. These values represent the rate of change of bearing db/dt, for a dt of one minute and the average true target bearing during the period for which the rate has been computed. These values are shown plotted on Plate IX and indicate that the relative course of the target is 120 degrees T. Since Plate IX is also a maneuvering board we may lay out the own course and speed vector of 000 degrees T, 3 knots, and transfer the relative course line to the end of the vector and for a target speed of 15 knots obtain a true course for the target of 110 degrees T.

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This method of obtaining the target's course is obviously laborious and subject to sonar errors and arithmetical errors of the plot recorder. In obtaining the target course by this method there are several points which should be remembered:

a. Even though each change of course by the target will produce a new relative motion line they will not be connected in such a manner as to produce a plotted track of the target.

b. Since the errors in the present JT sonar can be as much as plus or minus 1 to 2 degrees the value of db/dt which are plotted will vary considerably and the best that can be expected is a relative motion line obtained by "fairing" in the plotted points.

c. The inherent errors of the sonar system render it impracticable to plot values of db/dt of less than 2 degrees/mm.

d. Although a dt of one minute is used in the example smaller values may be used to obtain more plotted points without changing the graph itself or the answer desired. Experienced plotters will ordinarily use a value of dt = 30 seconds. This value of dt, however, cannot be changed during a problem.

e. The method will not work if continuous bearings are not available. Bearings obtained at intermittent intervals are of no practical value.

f. One erroneous bearing will cause two plotted points to be in error.

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g. When the target changes course an immediate change will occur in the rate of change of bearing (db/dt) and tile the change of course is in progress it will change at a varying rate which will continue until the target is steadied on its new course.

562. BEARING DIFFERENCE PLOT:

The Bearing Rate Plot as has been shown plots a varying amount of bearing change occurring over a fixed time interval. The Bearing Difference Plot plots a specified amount of bearing change occurring over a varying time interval. In the Bearing Difference Plot as in the Bearing Rate Plot the result obtained is the relative course of the target. (a) Plate XI is a Bearing Difference plotting sheet using a scale factor of twenty. The mathematical proof of this method is long and involved and will not be discussed. The formula used in the construction of a bearing difference plotting sheet is Tan B = X Tan A in which B is the angle between the Y axis and any radial line; A is the bearing difference angle and X is the scale factor. In Plate XI the tangent of angle B = 20 X tan 0.5 degrees or

Tan B = 20 X .0087
Tan B = .174
B = 99 degrees

In like manner radial lines representing each 1/4 degree of bearing difference are laid out up to 5 degrees.

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Beyond this varying difference angles are used as desired. The time scale used has no effect upon the solution obtained. A scale which will facilitate accurate plotting should be selected. It can be seen that increasing the scale factor will decrease the value of the minimum value of bearing difference which can be plotted for a given size of plotting sheet. When the rate of change of bearing of the target is large it will be found that a plotting sheet made up for a scale factor of ten or fifteen will give better results. Plate XII is a plotting sheet made up using a scale factor of ten.

The procedure for using this plot is as follows:

1. Start the stop watch on any even degree of bearing.

2. Label the Y axis as the reciprocal of this bearing.

3. Note the stop watch time and plot a point each time the bearing changes 1/4, 1/2, 3/4, etc., from that which obtained when the watch s started.

4. When enough points have been plotted to establish a line, measure the slope of this line. In Plate XI this is done by transferring the line to the origin and reading value of the slope on the vertical or horizontal scales around the maneuvering board plot. In Plate XII it is done by placing an overlay scale on the line as shown and reading the value directly.

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5. Apply this slope to the value of the Y axis determined in step 2. If the true bearing is increasing the slope is negative. If the true bearing is decreasing the slope is positive.

6. This is then the true direction of the target relative motion.

7. On the mooring board combine this value with own course and speed and known or estimated target speed to determine true target course. Each time the target changes course it is necessary to repeat again steps one through six.

(b) Plate XIII is a set of data plotted on Plate XI and labeled one (1). In this example the true bearing of the target was 000 degree T increasing. The "Y" axis is then 180 degrees T and the slope is 8 degrees. This gives a value of 172 degrees for the true direction of relative target course. This is then plotted on the maneuvering board to give a true target course of 171 degrees T. Note that the target changed course at 6 minutes and that points plotted at 06-15 and 06-17 indicate a definite change in the slope of the line. All changes of target course will be indicated in this manner.

(c) Plate XIV is another set of data in which there is a much larger rate of change of target bearing. This is shown plotted on Plate XI and labeled two (2). Note that a slope has been determined in 1 minute and 42 seconds. In the example the initial true bearing of the target was 010 degrees T increasing.

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The "Y" axis is then 190 degrees T and the slope is 50 degrees. This gives a value of 140 degrees T for the true direction of relative target course. This data is then plotted on the maneuvering board to give a true target course of 132 degrees T.

It can be readily seen that it is inconvenient to plot in the lower left hand corner of the plotting sheet. This can be prevented by using a plotting sheet made with a smaller scale factor. A second method is to double the time scale. The line labeled three (3) in figure XI shows the data of line two (2) plotted with the time scale doubled. Note, and this is important, that changing the time scale does not change the slope of the line.

It is sometimes desirable to plot bearing differences against equal increments of time instead of the method used in step 3 of the procedure. This does not vary the result and allows more points to be plotted with very low bearing rates.

(d) comparison of the Bearing Rate Plot and the Bearing Difference Plot as shown in the examples brings out the following points which should be noted in selecting the method to be used.

1. The greatest advantage of the Bearing Difference Plot over the Bearing Rate Plot is that bearing inaccuracies inherent with the sonar equipment are absorbed resulting in smaller and smaller percentage errors as the plot progresses.

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The Bearing Rate Plot uses bearing rates computed between one minute observations. The effect of the error of the sonar equipment for any given bearing rate will remain the same. In the Bearing Difference Plot this is not the case as the plotted values are always taken from a reference bearing. As the problem progresses the bearing difference becomes larger and larger and the percentage error becomes smaller and smaller.

Due to the inherent errors of our present sonar equipment the Bearing Rate Plot is not usable with a bearing rate less than 2 degrees/minute, The Bearing Difference Plot may be used at rates less than 1 degrees/minute.

As our sonar equipment is improved both plots will of course become more effective.

2. In the Bearing Rate Plot no data are available before an elapsed time of 1 minute. In the second example of the Bearing Difference Plot twenty-eight (28) points were plotted and a solution obtained in an elapse time of 1 minute, 30 seconds.

3. In the Bearing Rate Plot one bad bearing affects two plotted points. In the Bearing Difference Plot a bad bearing affects only one point.

4. In the Bearing Rate Plot a recorder and complicated arithmetic computations are required to obtain data. These are of course subject to error. In the Bearing Difference Plot no recorder is required and the data

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is obtained directly from the sonar bearing repeaters by observation.

5. In the Bearing Difference Plot where the angle on the bow of the target becomes larger than 30 degrees the slope of the line becomes very critical and a slight error in picking off the slope will introduce a fairly large course error. However, as the angle on the bow increases the target course becomes less and less critical in the fire control solution as the optimum torpedo track is approached.

563 - 569. BLANK

570. FIRING KEY OPERATOR:

(a) The Firing Key Operator mans the XJA phones and relays to the Torpedo Room all orders from the Approach Officer. The orders he is required to relay are the following:

1. Firing order.
2. Torpedo depth and speed settings.
3. The order to flood the tubes.
4. The order to open the outer doors.
5. The order to standby, commence shooting, and the order to check fire when necessary.

(b) When the tubes are flooded and the speed and depth are set on the torpedoes as ordered by the Approach Officer he relays the report from the Torpedo Rooms to the Fire Control Party that the Approach Officer's orders have been complied with. After the torpedo tube outer doors have been opened he informs the Approach

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Officer end the Fire Control Panty when the torpedo tubes are in all respects ready to fire.

(c) During firing he checks to see that the gyro angle set light on the firing panel is on prior to firing each individual torpedo. He fires each individual torpedo following the order SHOOT from the Assistant TDC Operator, holding the firing key down in each case a minimum of 5 seconds and times the firing interval to make sure that it is not less than that previously ordered by the Approach Officer.

571 - 579. BLANK

580. GYRO ANGLE SETTER:

(a) The Gyro Angle Setters are stationed in the gyro setting indicator regulators in the torpedo rooms. Their primary duty is to see that the correct gyro angles are being set on the torpedo tubes as directed by the Assistant TDC Operator.

(b) Upon manning battle stations the Gyro Angle Setters man the JA phones, set the gyro setting indicator regulator on 000 (180 aft), place the GSIR in automatic and stand by to report "manned and ready" when called by the Assistant TDC Operator. The Assistant TDC Operator then has complete control of the circuit. By closing the gyro angle indicating regulating switch on the TDC he can, at any time, complete the circuit and the correct gyro angle order will be transmitted to the tubes.

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(c) The Gyro Setting Indicator Regulator has adjustable mechanical stops. Both the Assistant TDC Operator and the Gyro Setter must know the limits set on the stops and must be alert to see that the gyro angle order is within the prescribed limits before matching.

(d) The Gyro single Setter must be alert for transmission failures and be ready to shift to hand at any time. If the Gyro Setting Indicator Regulator is secured for any reason after matching gyros the Gyro Angle Setter should immediately place the Gyro Setting Indicator Regulator on 000 (180 aft) by slew or hand, place the GSIR in in automatic and standby for further instructions from the Assistant TDC Operator. Failure to follow this procedure may result in running the Gyro Setting Indicator into the stops on the next matching, since the synchro system will tend to match in the shortest direction which in some cases would be through the stops. By placing the Gyro Setting Indicator Regulator always on 000 (180 aft) this will be avoided.

581. GYRO MATCHING AND CHECKING PROCEDURE:

At the critical range or when it becomes apparent which tube nest will be fired, the Assistant TDC Operator will match gyros and check then using the following procedure:

Assistant TDC Operator
GYROS FWD (AFT) MATCH
GYROS IN AUTOMATIC
Assistant TDC Operator completes the circuit by placing the gyro angle indicating regulating switch on the TDC is the indicating-regulating position.

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Gyro Angle Setter
TDC, GYROS FWD (AFT) MATCHED IN AUTOMATIC Gyro Angle Setter observes gyros matching and reports as soon as they are matched.
Assistant TDC Operator
GYROS FWD (AFT) STAND BY FOR A GYRO CHECK. STANDBY . . . . MARK! Marks the gyro angle order on an easily read value.
Gyro Angle Setter
ZERO FOUR ZERO TWENTY Reports the value of gyro angle order to closest ten minutes.
Assistant TDC Operator
CHECK Given then value reported by Gyro Angle Setter agrees with ATDC's observed value.

The Gyro Angle Setter then keeps observing the zero pointer and matching bug to see that they are matching. As long as they are matching, the Gyro Angle Setter will keep his gyro matched key closed giving a gyro matched light on the ready light panel. Should they get out of synchronism because of a large bearing change or spread entry the Gyro Angle Setter will release his gyro matched key until they are again in synchronism.

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CHAPTER 6

SPREADS

600. GENERAL:

(a) A spread is a salvo of torpedoes fired to hit different points along the length of the target or its length extended. This is illustrated in Plate XV. The successive torpedoes of the salvo hit at points A, B, and C.

(b) A salvo of torpedoes is spread to cover errors in the estimates of enemy's course, speed, and range (for large gyro angles). These errors are the total errors that might exist through the errors in the data used for firing, and those caused by routine or evasive maneuvers of the target just prior to, during, or shortly after torpedo fire occurs. The shorter the torpedo run, the greater is the angular length of the target. A smaller total percent coverage of target length may then be used to cover the estimated total errors.

(c) The unit of spread is the linear distance between adjacent points that torpedoes hit along the length of the target or its length extended. The unit of spread can also be expressed in the number of degrees it subtends at any given torpedo run on any given torpedo track angle.

(d) The total amount of spread used in a salvo may be spoken of in terms of total percentage of target length covered.

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In the diagrams on Plate XV the total amount or spread is 100%.

(e) The number of torpedoes in a salvo is determined by the number of hits desired with any given total coverage.

601. GYRO ANGLES:

(a) The difference in gyro angles between successive torpedoes in a salvo determines the pattern of the salvo.

(b) When firing a salvo to hit the same point of aim of a moving target, the difference in gyro angles between successive torpedoes is the Target Advance Angle. It should not be confused with spread.

(c) When firing a salvo which is spread to hit at different points along the target's length or length extended, the difference in gyro angles is equal to the algebraic sum of the Target Advance Angle and the Spread Angle.

(d) This difference in gyro angle, and therefore the pattern of a spread, can be varied in any given salvo by changing the order in which the successive torpedoes are fired to hit along the target's length or length extended.

(e) The following example will illustrate this statement. In this example a uniform firing interval is assumed for the sake of clarity.

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EXAMPLE - Three torpedoes are to be fired on a 90 degrees starboard torpedo track angle with a torpedo run of 960 yards. Target 600 feet (200 yards) in length is making 17.5 knots, 100% coverage is desired. Firing interval 10 seconds. Generated gyro angle order 356 degrees.

CASE 1: All torpedoes have gone out on the same track. The salvo, therefore, is a longitudinal spread. This is a special case, as previously mentioned, but clearly shows that divergence will be quite small in firing from forward to aft. Firing Forward, M.O.T., Aft, is particularly recommended against a high speed target at short range, in order to keep rate of change of gyro angle order to a minimum, thereby insuring matched gyros at instant of firing.

Illustration of three torpedos on the same track hitting in three locations of the target.

TORPEDO
#1
TORPEDO
#2
TORPEDO
#3
Generated Gyro Angle Order 356 degrees 002 degrees 008 degrees
Target Advance Angle 6 degrees
Spread Angle 6 degrees R 0 degrees 6 degrees L
Indicated Gyro Angle Order 002 degrees 002 degrees 002 degrees

Difference 0 degrees

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CASE 2: A divergent spread with the greatest divergence will always be obtained when firing from aft forward.

Illustration of spread with different gyro angles.

TORPEDO
#1
TORPEDO
#2
TORPEDO
#3
Generated Gyro Angle Order 356 degrees 002 degrees 008 degrees
Target Advance Angle 6 degrees
Spread Angle 6 degrees L 0 degrees 6 degrees R
Indicated Gyro Angle Order 350 degrees 002 degrees 014 degrees

Difference 12 degrees

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CASE 3: A divergent spread: When firing at the M.O.T., forward, and then aft, a spread of moderate divergence will be obtained.

Illustration of spread with different gyro angles.

TORPEDO
#1
TORPEDO
#2
TORPEDO
#3
Generated Gyro Angle Order 356 degrees 002 degrees 008 degrees
Target Advance Angle 6 degrees
Spread Angle 0 degrees 6 degrees R 6 degrees L
Indicated Gyro Angle Order 356 degrees 008 degrees 002 degrees

Difference 6 degrees

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CASE 4: A divergent spread of unsymetrical pattern is obtained when firing at the M.O.T., aft, and then forward.

Illustration of spread with different gyro angles.

TORPEDO
#1
TORPEDO
#2
TORPEDO
#3
Generated Gyro Angle Order 356 degrees 002 degrees 008 degrees
Target Advance Angle 6 degrees
Spread Angle 0 degrees 6 degrees L 6 degrees R
Indicated Gyro Angle Order 356 degrees 356 degrees 014 degrees

Difference 0 degrees-18 degrees

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602. TYPES OF SPREAD:

(a) Divergent Spread

A divergent spread is a spread in which the torpedoes of a salvo intersect the target's track at different points along the target's length and at different torpedo track angles. This type of spread is difficult to avoid because of its fan-shaped pattern. (Diagram A, Plate XV).

(b) Longitudinal Spread

A longitudinal spread is the spread obtained by firing a salvo of torpedoes along identical torpedo tracks. Torpedo #1 hits the target at A, #2 at B, and #3 at C, due to movement of target across the identical track of the torpedoes. It is a simple type of spread, having the disadvantage that the target which can avoid one torpedo track undoubtedly can avoid the others which are following in the wake of the first. (Diagram B, Plate XV).

(c) There are many different types of spreads which may be used. During the war numerous "gadgets" were designed and used in setting spreads. No matter what spread is used it should embody certain basic elements. These are:

1. Target length
2. Torpedo track
3. Torpedo run
4. Coverage

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Any spread system should combine these four elements to produce the spread desired. Two types of spread determination in common use will be discussed in detail below.

603. COMPUTED SPREAD:

(a) The computed spread is based on the fact that 1 degree subtends approximately 100 feet at 2000 yards. From this the formula may be deduced:

No. Degrees Total Spread= (Tar. Length in Feet/100) X (% Coverage) X (2000/Torpedo Run) X (SIN TTa)

(b) The main advantage of this spread is that the Approach Officer may designate exactly the coverage be desires for any given situation. Also no "gadget" is required.

(c) The following table should be used for the sine of the torpedo track angle.

Torpedo Track Sine
15-30 1/4
30-45 1/2
45-60 3/4
60-90 1

(d) The following table should be used for torpedo run.

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Torpedo Run Actual Torpedo Run Used
700 - 1250 1000
1250 - 1750 1500
1750 - 2250 2000
2250 - 2750 2500
2750 - 3250 3000

(e) The torpedo track angle and the torpedo run are quick estimates made by the Assistant TDC Operator. The above tables are well within the accuracy of his estimates. The tables greatly simplify the computations necessary.

(f) When the Total Spread is obtained the Unit of Spread may be quickly calculated by dividing by one less than the number of torpedoes to be fired.

(g) The main advantage of this spread is that the Approach Officer may designate exactly the coverage he desires for any given situation. Also all elements are considered and no "gadget" is required. This spread should not be used with a torpedo track of less than 15 degrees.

604. 4-3-2-l SPREAD:

(a) The 4-3-2-1 spread is a simple variation of the computed spread. It has been designed to produce a 70 yard average linear unit of spread, and is primarily intended for a 600 foot target. This factor is the inherent weakness of the method which is, however, compensated for by its simplicity of determination and application. Since it produces a set value of angular unit of spread the coverage obtained is not readily ascertainable.

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The values of angular unit of spread are derived from the table using the torpedo run as the determining element. The unit of spread must be adjusted for the torpedo track angle as in the computed spread.

Unit of Spread   Torpedo Run
4 ) Multiplied  700 - 1500
3 ) by sine of  1500 - 2000
2 ) the torpedo  2000 - 2500
1 ) track angle  2500 - 3000

This spread should not be used with a torpedo track of less than 15 degrees.

(b) Regardless of the spread system used ten firing on a torpedo track of less than 15 degrees not more than 1/2 degrees total spread should be used.

605. SPREAD POLICY:

In determining the spread policy to be used aboard a submarine the following points should be remembered:

(a) A longitudinal spread gives no divergence.

(b) Spreading from aft-forward gives the maximum divergence.

(c) A spread should be very easy to compute and apply to avoid personnel errors.

(d) Use equal units of spread between adjacent torpedoes in a salvo.

(e) Linear unit of spread should not exceed effective target length. It is mandatory that a spread policy be established on every submarine and that the Fire Control Party understand it thoroughly and that they be drilled in its use.

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606. DETERMINATION OF COVERAGE:

The Approach Officer should bear the following points in mind in determining the amount of spread to be used:

(a) The Probable magnitude of the errors caused by routine or evasive maneuvers of the target prior to, during, or shortly after torpedo fire occurs. This will be influenced by:

(1) Torpedo run
(2) Torpedo track angle
(3) Tactical characteristics of the target
(4) Ratio of torpedo speed to target speed

(b) The probable magnitude of the errors in the firing data and torpedo performance.

(c) Sufficient number of torpedoes in the salvo to obtain the desired number of hits from the salvo consistent with the need of providing proper coverage for the probable total errors.

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CHAPTER 7

FIRING METHODS

700. GENERAL:

(a) Firing methods describe the different procedures employed just prior to and while firing the torpedoes of a salvo. Good firing methods insure the most effective torpedo fire for the firing data used. The torpedo Fire Control Party must be well trained in the use of any selected method or methods.

(b) The TDC generates a hitting gyro angle for any instantaneous relative bearing of the target and the estimated values of target speed, target course, end range. The accuracy of this gyro angle will vary with the accuracy of these estimates to the degree that an error in any one might be accumulated with or cancel out all or part of another. Regardless of the position at which torpedo fire occurs, every effort is made to have the most correct solution on the TDC while firing. This is accomplished by the use of firing methods which insure that:

(1) An accurate relative bearing of the target is in the TDC upon firing.

(2) An accurate range is in the TDC upon firing when using large gyro angles.

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(c) The following basic standard firing methods are described for submerged attacks but are equally applicable to surface attacks, they are:

(1) Check baring method
(2) Continuous bearing method
(3) Constant bearing method

701. CHECK BEARING METHOD:

(a) The Approach Officer having previously announced that SHOOTING WILL BE BY THE CHECK BEARING METHOD, BEARING EVERY ____ TORPEDOES. He then, when in all respects ready to shoot, announces FINAL BEARING AND SHOOT - UP SCOPE.

(b) A designated member of the Fire Control Party orders STANDBY FORWARD (AFT).

(c) The periscope is placed on the desired point of aim as soon as the top of the periscope breaks water. The Approach Officer orders BEARING MARK.

(d) The TDC Operator matches the observed bearing and radar range (if taken) in the center, section of the TDC and announces SET when it has been matched.

(e) The Assistant TDC Operator announces SHOOT if the following conditions are met:


(1) Spread set
(2) Correct solution light on

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(f) If the gyro matched light is on, the firing key operator presses the firing key, announces FIRE ONE, and starts his stop watch. He announces ONE FIRED when the torpedo has left the tube.

(g) If the target is not tracking well, this procedure is repeated for each torpedo in the salvo. When the target is tracking well on the TDC, in the interest of reducing the probability of being sighted, the number of check bearings inserted may be reduced. It is undesirable, however, to fire more than two torpedoes in succession without a check bearing.

(h) The TDC Operator announces SET only when a check bearing is obtained.

(i) The Assistant TDC Operator must announce SHOOT prior to the firing of each torpedo. If a check bearing is not obtained after the torpedo has been tired as announced by the Firing Key Operator, the Assistant TDC Operator must insure that the preceding torpedo has left the tube prior to setting the spread for the next torpedo.

(j) The Firing Key Operator must wait for the order SHOOT prior to firing each torpedo even if the firing interval is exceeded. Under normal circumstances he will receive the order SHOOT prior to the end of the firing interval. He then must fire on time. As successive torpedoes are fired be announces TWO FIRED, THREE FIRED, ETC.

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702. CONTINUOUS BEARING METHOD:

(a) The Approach Officer having previously announced that SHOOTING WILL BE BY CONTINUOUS BEARING METHOD he then, when in all respects ready to shoot, announces FINAL BEARING AND SHOOT - UP SCOPE.

(b) A designated member of the Fire Control Party orders STANDBY FORWARD (AFT).

(c) The periscope is placed on the desired point of aim as soon as the top of the periscope breaks water. The Approach Officer announces BEARING ON as long as he has the cross wire of the periscope on the desired point of aim. He announces BEARING OFF while shifting to a new point of sin, or if the cross wire should inadvertently move off the desired point of aim.

(d) The TDC Operator matches the generated and observed values of relative bearing and radar range (if taken) in the center section of the TDC. The TDC Operator announces SET as soon as he has matched and thereafter keeps the observed and generated values of relative bearing matched throughout the firing.

(e) The Assistant TDC Operator orders SHOOT when the following conditions are met:


(1) Spread set (if not applied at periscope)
(2) Correct solution light on

(f) The Firing Key Operator announces FIRE ONE if the gyro matched light is on.

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(g) Assistant TDC Operator and Firing Key operator follow the same procedure as under the Check Bearing method when no check bearings are being obtained.

703. CONSTANT BEARING METHOD:

(a) The Approach Officer having previously announced SHOOTING WILL BE BY CONSTANT BEARING METHOD he then, when in all respects ready to fire, announces FINAL BEARING AND SHOOT UP SCOPE.

(b) A designated member of the Fire Control Party orders STANDBY FORWARD (AFT).

(c) The periscope is placed ahead of the desired point of aim as soon as the top of the periscope breaks water. The Approach Officer announces BEARING MARK.

(d) The TDC Operator matches the generated and observed relative bearing on the center section of the TDC and stops the generation by holding this value constants He then announces SET.

(e) The Assistant TDC Operator announces SIDOT when the following conditions have been met:


(1) Correct solution light on
(2) Gyro matched light on

(f) the Approach Officer orders FIRE one when the point of aim crosses the vertical cross wire at the periscope which has been left on the original relative bearing. The TDC Operator then releases the relative bearing hand crank and allows the TDC to generate.

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(g) This procedure is repeated for each desired point of aim, unless a longitudinal spread is being fired. In this event, the original bearing is held constant throughout the salvo.

(h) The Firing Key Operator fires each torpedo on the order of the Approach Officer.

(i) In all of the above methods, if it becomes necessary to stop shooting due to a target zig or any other reason the order CHECK FIRE should be given. After CHECK FIRE is ordered firing should be resumed in the sane manner as originally commenced. It must be remembered that if some torpedoes of a salvo have been fired that the effectiveness of the spread will be reduced if fire is not resumed with a minimum of delay.

704. ADVANTAGES AND DISADVANTAGES OF THE FIRING METHODS:

(a) Check Bearing


(1) Minimum periscope exposure is obtained.
(2) A satisfactory accuracy of target bearing in the TDC is obtained.

(b) Continuous Bearing


(1) The correct target bearing is maintained in the TDC.
(2) Periscope is exposed throughout the firing.

(c) Constant Bearing


(1) The correct target bearing is maintained in the TDC.
(2) The Angle Solver solution is steady ten each torpedo is fired.

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(3) Periscope is exposed throughout the firing.

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CHAPTER 8

THEORY OF THE APPROACH AND ATTACK

800. GENERAL

The Approach and Attack is divided into three phases; namely the contact phase, the approach phase, and the attack phase.

(a) The purpose of the contact phase is to determine the direction of relative movement of the target.

(b) The purpose of the approach phase is to close the target in order to bring the submarine within torpedo range of the target.

(c) The purpose of the attack phase is to maneuver the submarine into the most favorable firing position obtainable under the circumstances.

801. BASIC FUNDAMENTALS OF THE APPROACH AND ATTACK

Methods of determination of Direction of Target Motion.

802. Target not in sight.

(a) Upon making contact with a target the submarine must determine immediately the approximate course of the target. In many cases contact is made from smoke or the top of a mast. In this event the submarine must determine the direction of change of true bearing in order to establish the direction of target motion. Once the direction of the change of true

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true bearing is determined, the angle on the bow is then established as port or starboard and the submarine placed on a course to close the target's track.

(b) When a contact is made by radar, ranges and bearings are then immediately available and the direction of motion as well as course of the target may be quickly established by navigational plot, The "speed zero" method as described in OP1442A may also be used to obtain the direction of target motion and course in this case.

803. Target in sight.

(a) When the target is in sight the quickest and simplest way to determine the direction of target motion is by visual observation of angle on the bow.

(b) Estimation of angle on the bow by observation through a periscope is one of the arts peculiar to submarining. An officer's ability to accurately estimate angles on the bow increases directly with his experience in submarines.

(c) The most common error in estimation of angles on the bow is that of over-estimation which often can be ascribed to one or more of the following reasons:

(1) Lack of appreciation that the effective length of the target varies with the sine of the angle on the bow. Half of the target length is seen with a 30 degrees angle on the bow, seven tenths with a 45 degrees angle

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on the bow and nine tenths with a 60 degrees angle on the bow.

(2) Lack of depth perception when using a monocular periscope.

(3) The illusion that a target is changing course away; this is very marked at short ranges caused by the high relative angular motion of the target across the line of sight.

(4) The illusion of a target being on a steady course when viewed at short ranges during a change of course of a target towards e. submarine. This illusion is created by a partial or total cancellation of the apparent relative motion of the target across the line of sight by the course change of the target toward the submarine.

(5) Clever camouflaging may also increase the difficulties of angle on the bow estimation.

(6) Determination of target course by angle on the bow estimation is much more difficult with large angles on the bow (over 30) than with small angles on the bow.

(7) The method of obtaining angle on the bow by plot has been discussed in detail in Chapter 5.

Plot and TDC determination of target motion must be weighed against the observed angle on the bow. The accuracy of Plot and TDC solutions of target course varies greatly with the type of information furnished.

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(8) When using Stadimeter or Telemeter scale ranges Plot and TDC solutions of target course are usually not as good as the observed angle on the bow and far more weight should therefore be given to t observed angle on the bow. However, when radar ranges are available Plot and TDC solutions of target course are very accurate and should be given a great deal of weight. In the case of large angles on the bow which are difficult to estimate by eye, Plot and TDC solutions, when using radar ranges, are almost invariably better than observed angles on the bow.

804. SPEED DETERMINATION:

(a) The Fire Control Party must utilize every means at their disposal to determine target speed. The following means are available:

(1) TDC This method is described in OP1442A.
(2) PLOT This method is described in detail in Chapter 5.
(3) TURN COUNT The Approach Officer should have available for ready reference the most complete set of curves that he can obtain of different types and classes of enemy vessels. Their use will furnish a means of approximating the speed of an observed target.

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Due consideration must, of course, be given to wind and sea conditions and condition of loading as they increase or decrease the speed of any given R.P.M. Turn count is most valuable in determining a sudden change of target speed.
(4) Type of Vessel Knowledge of maximum and cruising speeds of various types of ships is of some aid.
(5) Intelligence Any previous information furnished from other sources will be of assistance in determining speed.

(b) Although five methods of determining speed have been given above, it still remains that under almost all circumstances Plot and TDC are the two primary methods which the submarine must employ to obtain target speed. In both of these methods any error in underwater log speed will introduce a corresponding error in solution of target speed.

805. RELATIVE MOVEMENT

(a) Constant True Bearing

(1) When the range is decreasing and the true bearing of the target remains constant the submarine and the target are on a collision course. In Plate XVI the true bearing is remaining constant at 015 degrees T and

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if both ships maintain course and speed they will collide at point A.

(2) If during the period between two observations of the target the true bearing remains constant and the target has not changed course, the angle on the bow will remain the sane.

In Plate XVI angle Ab = angle b

(3) If the target and the submarine have not changed course, the target has not changed speed, and the true bearing has remained constant over a period of 2 to 3 minutes, the target speed may be determined by the formula under plate XVI.

(b) Change in True Bearing

(1) When the submarine is closing the target's track and the true bearing is drawing towards the bow the submarine is losing true bearing and the target will pass ahead of the submarine.

(2) When the submarine is closing the target's track and the true bearing is drawing towards the stern the submarine is gaining true bearing and will cross the target's track ahead of the target.

(3) If the true bearing of the target changes and the target does not change course the angle on the bow of the target will change the same amount as the true bearing. If the submarine is gaining true bearing the angle on the bow will decrease and if the submarine is losing true bearing the angle on the bow

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will increase by the amount of change of true bearing.

(c) Speed When Abeam

When abeam of a vessel, the rate of change of bearing in degrees per minute is equal to 1 degrees per knot of enemy speed at 2000 yards. The above statement disregards any change of bearing due to the submarine movement. It is reasonably accurate between angles on the bow of 50 to 130. It is based on the fact that 1 degrees subtends 35 yards at a range of 2000 yards and one knot equals 33 yards per minute.

(d) Relative Bearing

Turning towards or away from the target will bring the relative bearing of the target closer to, or further from the bow, respectively, by the amount of the course change.

(e) Submarine Track

In any situation the track that the submarine is on may be quickly determined by adding together the angle on the bow and the lead angle.

(f) Distance to Track

The distance to the track is equal to the sine of the angle on the bow times the range. This may be approximated by the formula:

Distance to Track = (Ab / 60) X Range

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Also the fact that the sine of the Ab changes .1 every 6 degrees up to 60 degrees may he used as shown in the following table:

sine 6 degrees - .1  sine 36 degrees - .6
10 degrees - 1/6  40 degrees - 2/3
12 degrees - .2  41-48 degrees - .7
15 degrees - 1/4  49-58 degrees - .8
18 degrees - .3  59-65 degrees - .9
20 degrees - 1/3  66-90 degrees - 1.0
24 degrees - .4 
30 degrees - 1/2 

806 - 809. BLANK

810. ANALYSIS OF TORPEDO FIRING:

(a) Straight Fire

Torpedo firing in which small gyro angles (less than 30 degrees) are used is considered to be "Straight Fire". The curves plotted on plates XVII and XVIII for 46 and 29 knot torpedoes were developed by plotting the deflection angle against the torpedo track angle for different target speeds. It should be noted that in all cases the gyro angle was zero.

(b) The slope of these curves at any point is the instantaneous rate of change of deflection angle with torpedo track angle. The optimum torpedo track angle for any given target speed is the torpedo track angle for which the rate of change of deflection angle is the least. This is indicated on the curves by the shaded areas.

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(c) It is within this range of torpedo track angles that the greatest amount of course error can be absorbed. From a study of the curves it is evident that the maximum deflection angle is obtained when firing on the optimum torpedo track angle and that the optimum torpedo track angle has a value equal to 90 degrees plus the maximum deflection angle. It is also evident that as the target speed increases for any given torpedo speed the slope of the curves becomes sharper. This means that the higher the target speed the greater the rate of change of deflection angle with torpedo track angle. It is therefore true that the optimum torpedo track angle is more effective for absorbing errors in course when the ratio of torpedo speed to target speed is large. It therefore may be stated that the optimum torpedo track angle is a good mean torpedo track angle for firing a salvo of torpedoes if the target speed is less than one-half of the torpedo speed.

(d) The optimum torpedo track angle for a 16 knot target for a 46 knot torpedo is about 110 degrees and for a 29 knot torpedo about 125 degrees.

(e) The greatest advantage of straight fire (small gyro angles) is that errors in torpedo run have no appreciable effect on the solution. Therefore, when the range is inaccurate, as in stadimeter and telemeter scale approaches, the submarine must maneuver for a small gyro angle shot.

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811. CURVED FIRE:

Torpedo firing in which large gyro angles (over 30) are used is considered to be "Curved Fire".

(a) When using curved fire an additional angular correction must be applied to the deflection angle to correct for reach and turning circle of the torpedo. This correction is automatically computed in the angle solver section of the TDC. This correction varies with torpedo run. The following table was made up by setting up the TDC for target speeds of 10, 15, and 20 knots and adjusted for a starboard 90 degrees torpedo track and 1000 yard torpedo run with gyro angles of 20, 40, 60 and 90 left in each case. The torpedo run was then increased to 1200 yards and the gyro angle difference recorded.

Target Speed 10 kts. 15 kts. 20 kts.
Left Gyros Gyro Angle
Diff.
Gyro Angle
Diff.
Gyros Angle
Diff.
20 .5 degrees 0 degrees .5 degrees
40 1.5 degrees 1.5 degrees 2 degrees
60 2 degrees 2 degrees 2.5 degrees
90 5 degrees 4.5 degrees 5 degrees

From examination of this table it may be readily seen that for a torpedo run error of 200 yards as the gyro angle increases the angular error becomes larger and larger.

(b) In order to have a correct solution of torpedo run it is mandatory that an accurate range be available.

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"Curved Fire" should not be used ten an accurate range is not available.

(c) When radar ranges are available it is not necessary to maneuver to obtain small gyro angles. It has been found in many firings at the Submarine School that when using radar ranges the percentage of hits obtained is the same with "Curved Fire" as with "Straight Fire".

812 - 819. BLANK

820. ANALYSIS OF TORPEDO TRACK ANGLES:

(a) Effective Target Length

The effective length of the target is determined by the torpedo track used. On a 90 degrees torpedo track the effective length is the actual length. On either side of 90 degrees the effective length is less than the actual length and may be determined by multiplying the sine of the torpedo track angle by the actual target length. On a 30 degrees torpedo track the effective target length is of the actual target length. On a 60 degrees or 120 degrees torpedo track the effective target length is .9 of the actual target length. On a 0 degrees or 180 degrees torpedo track the effective target length is the beam of the target. It may readily be seen that a torpedo track between 60 and 120 is the most advantageous from the standpoint of effective target length.

(b) Course Errors

The greatest course error can be absorbed when firing on the optimum torpedo track see paragraph 810(c).

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As the torpedo track angle decreases the course becomes more and more critical. When firing on a 0 degrees or 180 degrees torpedo track speed errors have no effect and course is the primary consideration. No course error can be absorbed under this condition.

(c) Speed Errors

Speed errors have no effect when firing on a 0 degrees or 180 degrees torpedo track, because, in this situation target speed affects only the torpedo run. AS the torpedo track increases towards 90 degrees, speed errors have a greater and greater effect on the solution. Therefore it would theoretically be best to shoot on a sharp torpedo track to compensate for speed errors This is not practical, however, because of the radical reduction in effective target length on sharp torpedo tracks. In the final analysis the only practical ay to compensate for speed errors is by the use of an adequate spread.

821 - 829. BLANK

830 DOWN THE THROAT SHOT:

A "down the throat shot" is considered to be a shot where the torpedo track is 15 degrees or less.

In this type of shot the primary consideration is target course. A two degree target course error will result in approximately one degree of gyro angle error. This is unacceptable in most cases because the effective target length is so small. Also it is impractical to use a large spread in this case because the distance between torpedoes at the target's track should not exceed the effective target

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length. Against most targets the natural dispersion of the torpedoes in this type shot constitutes sufficient spread. In any event no more than 1/2 degree total spread should be used.

Speed has no appreciable effect on a "down the throat shot". Range has no effect when using zero gyros. "Down the throat" angled shots should not be attempted unless a radar range is available.

Due to the inherent errors of the Submarine Fire Control System it is not considered feasible to shoot a "down the throat shot" with greater than a 1500 yard torpedo run.

831 - 839.

BLANK 840. DEFLECTION ANGLE FOR STRAIGHT FIRE:

The deflection angle for a straight shot of any torpedo run for target speeds less than one-half the torpedo speed, may be approximated as follows:

Torpedo
Track Angle
  46 Knot Torpedo   29 Knot Torpedo
1. 90 degrees   1 1/4 x Target Speed   2 x Target Speed
2. 60 degrees   75% of (1)   75% of (1)
3. 40 degrees   50% or (1)   50% of (1)
4. 18 degrees   25% of (1)   25% of (1)
5. Optimum   1-1/3 x Target Speed  

841 - 849. BLANK

850. APPROACH COURSES:

851. NORMAL COURSE:

The normal course is the course which will close the target's track fastest for any given speed.

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852. NORMAL APPROACH COURSE:

The normal approach course is directly across the line of sight. It is the best course for maintaining or gaining true bearing on the target.

853. OPTIMUM APPROACH COURSE:

The Optimum Approach Course will bring the submarine to a firing position against the Widest possible range of target actions by virtue of successfully closing targets which would be lost with any other approach course.

It should be used until there is no longer any doubt about being able to close the target to within limiting torpedo run.

Usually the Optimum Approach Course lags the Normal Approach Course by about 10 degrees.

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CHAPTER 9

SUBMERGED APPROACH AND ATTACK TACTICS

900. GENERAL

The fundamental purpose of the approach and attack is to destroy the enemy with the primary offensive weapon of the submarine, i.e., torpedoes. The submerged approach and attack demands the utmost skill on the part of the Approach Officer and the Fire Control Party to maneuver the submarine into the optimum firing position. The low speed and poor maneuverability of the submarine and the limited opportunities for observing the target require prompt and correct action by even member of the Fire Control Party based on the information available.

901. THE CONTACT PHASE

The objective of this phase is to determine the direction of relative movement of the target. When contact is made with the masts or smoke of a target on the horizon no angle on the bow can be visually obtained. The submarine must then determine the direction of the angle on the bow (port or starboard) by some other means. This should be done by observing the direction of change of the target's true bearing. In order to obtain the maximum effect of change of true bearing due to the target's movement the submarine should be turned to head directly at the target or directly away from the target. Once the angle on the

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bow has been established as either port or starboard the submarine should assume that the target is presenting a moderately large angle on the bow and is using high speed. An Optimum Approach course which lags the Normal Approach course by 10 degrees should be taken at high speed. The Contact Phase is then completed and the Approach Phase is started.

902. THE APPROACH PHASE

(a) The basic objective of the Approach Phase is to close the target in order to bring the submarine within torpedo range of the target and to attain the best possible position from which to commence the attack. The low speed and poor maneuverability of the submarine make it mandatory that prompt and correct action be taken in order to insure attaining a position from which an attack can be made regardless of subsequent movements of the target. The best position is, therefore, directly ahead of the target at a range which will allow time for the submarine to maneuver to a favorable firing position.

(b) When the submarine commences to maneuver to a favorable firing position, the Approach Phase is over and the Attack Phase has begun. The submerged submarine's greatest problem is to attain a good position from which an attack can be delivered.

(c) A bad tactical mistake that can be made by the submerged submarine when first making contact with an enemy whose tops or smoke is just visible over the horizon,

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is to delay in commencing aggressive and well planned approach tactics. In the training area or on the attack teacher, the target in the majority of the cases may be generally depended upon to come within torpedo range if a submarine makes a minimum effective effort to close the target track through ill chosen and unimaginative tactics. The Approach Officer may, consequently, develop a false appreciation of the tactical problem that is the general one at sea. This is, that the enemy might not be brought within torpedo range unless intelligent tactics are used from first contact and continued throughout the Approach Phase. The arbitrary use of the Normal Approach Course might, in borderline cases, result in the failure of the submarine to achieve a position inside the maximum torpedo run.

(d) The submarine which makes contact with the masts or smoke of a target well over the horizon should assume that the target is presenting a moderately large angle on the bow and is using a high speed. An Optimum Approach Course which lags the Normal Approach Course by 10 degrees should be taken at high speed. With no other information, such tactics should result in a fair approximation of the actual maneuvering board solution for the OAC. When the Approach Officer estimates that sufficient time has elapsed so that another true bearing and radar range will afford a good course and speed analysis; or, if not equipped with periscope radar,

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estimates that the range to the target has decreased sufficiently to permit an accurate visual estimate of angle on the bow and range, he should then slow to take such observations.

(e) If the target is actually presenting a large angle on the bow on the same side as initially estimated, the Approach Officer should continue to use the OAC to insure the maximum probability of closing to a point inside of maximum torpedo run.

(f) If the observation discloses that the enemy is showing small angles on the bow (less than 20 degrees), or is showing an opposite angle on the bow than originally estimated, the submarine should then be maneuvered in accordance with the prescribed Approach Phase Doctrine given below. This doctrine is a guide to good tactics for submerged submarines during the Approach Phase.

APPROACH PHASE DOCTRINE


Angle Angle on the Bow Lead Angle Average
Submarine Speed
0 degrees 0 degrees 2 (dead slow)
5 degrees 30 degrees 3 (1/3 speed)
10 degrees 45 degrees 4 (2/3 speed)
15 degrees 65 degrees 5 (standard)
20 degrees or greater 90 degrees (NAC) 6 to 8 (standard to full)

THE ABOVE DOCTRINE IS A FLEXIBLE GUIDE TO GOOD BASIC TACTICS. WHERE LOGIC, COMMON SENSE OR SPECIAL CONDITIONS DICTATE, IT SHOULD BE MODIFIED ACCORDINGLY.

(g) The above doctrine is based upon maneuvering board solutions for collision courses with a 17.5 knot target.

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It is easily appreciated that a target which consistently changes course away from a submerged submarine will never be closed. Any tactics which fail in any degree to maintain a collision course with a target will result in effective course changes away by the target at the same rate the true bearing is "lost". THE OPTIMUM IN TACTICS FOR THE SUBMERGED SUBMARINE IS THEREFORE TO MAINTAIN OR BETTER THAN MAINTAIN A COLLISION COURSE WITH THE TARGET.

(h) Although the Normal Approach Course will afford the best possibility of achieving the optimum in tactics, the use of the NAC when the angle on the bow is small is faulty tactics. Under such circumstances the use of smaller lead angles will suffice to give a reasonable chance of maintaining a collision course, and at the same time place the submarine in a better position in the event of a subsequent course change away.

(i) In applying the above doctrine it is mandatory that sufficient observations be made to insure obtaining target speed during the Approach Phase.

903. THE ATTACK PHASE

(a) The Approach Phase ends and the Attack Phase begins when the Approach Officer ceases his efforts to close the target and commences to maneuver the submarine into the most favorable firing position obtainable under the circumstances.

(b) The submarine may or may not have been able to close to the best position for commencing the Attack Phase.

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The submarine's efforts to close the target may have only been successful enough to reach a firing position just inside maximum torpedo run and may be actually outside of the critical range when firing takes place.

(c) Under the circumstances that the submarine has been successful in closing to a favorable position for commencing the attack the problem may be resolved into four typical situations. All of these situations are based on certain fundamental precepts which follow:


1. The fact that at the critical range (equal to a 7 1/2 minute run of the target) a decision must be made as to subsequent tactics to be followed by the submarine.

2. The fact that the average length of leg of most zig zag plans is six minutes.

(d) In applying these situations the following should be borne in mind:


1. The critical range should be based on the highest reasonable estimate of target speed.

2. The target should be observed a minute or two before the critical range is reached.

3. The Approach Officer should strive to anticipate the various situations that might develop at the critical range, and make preliminary decisions to cope with them.

4. The situation in which the submarine finds itself must be determined at the critical range. Whenever the critical range is reached one of the four situations will apply.

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(e) The Approach and Attack chart, Plate XIX describes the Approach Doctrine and the tour situations in brief. Each situation will be described in detail in the following pages.

(f) In each of the four situations to be discussed, the submarine is assumed to be at the critical range.

904. SITUATION ONE

(a) The following conditions obtain:


(1) The distance to the track is 1000 yards or less.

(2) The target has zigged within the last 2 minutes.

(b) First Course of Action

Target is nearly on the submarine's beam. (See Plate XX). Turn away from the target to approximately a parallel course. The target has changed course in the last two minutes and may, therefore, not be expected to zig shortly. Turning away will keep the rate of change of range to a minimum while awaiting the next change of target course. It is mandatory that the next change of course be promptly detected either by periscope or sonar. After the zig the submarine should be maneuvered to obtain the best possible shot with a stern tube.

In this situation time is of the essence and the Approach Officer must carefully weigh the advisability of slowing for an observation by periscope or sonar against the necessity for maintaining speed in order to attain a favorable firing position.

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(c) Second Course of Action

Target well forward of the beam. Plate XXII. Close target on sharp track as under these circumstances it is impractical to attempt to make the large course change necessary to parallel the target. Firing position will be reached very shortly. The submarine, therefore must fire on the present leg and must accept the probable sharp torpedo track angle existing at the firing point.

905. SITUATION TWO

(a) The following conditions obtain:


(1) The distance to the track is 1000 yards or less

(2) The target has not zigged within the last 2-minutes.

(b) Course of Action

The target is expected to zig shortly. Plate XXI The Approach Officer should have previously observed the target on the present course and should have the submarine on a course which is closing the target's track. Continue closing the target's track. Wait for next the zig. After the target has changed course maneuver for the best shot obtainable with either bow or stern tubes. The normal expectancy in this situation is a bow tube shot. However, the decision as to which tubes should be used must be based on the distance to the track aft after the course change.

906. LIMITATION ON COURSE OF ACTION SITUATIONS I AND II

In both situations I and II the distance to the track at the critical range is less than 1000 yards. If the target does not change course as expected the submarine

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is in danger of being "run down". It is, therefore necessary to commence shooting regardless of the time on the leg when the minimum torpedo run has been reached. The minimum allowable torpedo run is 700 yards. However, in order to complete firing a salvo of torpedoes it is necessary to commence shooting prior to this time. This is a function of target speed but for a medium speed target if firing is commenced with a 1200 yard torpedo run the last torpedo will be fired with the required minimum of 700 yards torpedo run. Therefore, as a general rule, when the torpedo run has reached 1200 yards, in situation I and II, start shooting regardless of other considerations. Don't get "run down".

907. SITUATION THREE

(a) The following conditions obtain:


(1) The distance to the track is more than 1000 yds.

(2) The target has zigged within the last 2 minutes.

(b) Course of Action:

(See Plate XXIII). The target has zigged within the last two minutes and therefore is not expected to zig for some time. The submarine will fire on the present leg with the best torpedo track obtainable under the circumstances. The submarine must, however, shoot in time to have the torpedoes reach the target before the target is expected to zig (six minutes on the leg). Allowing for a two minute torpedo run, a good general rule in this situation is to start shooting when the target has been not longer than four minutes on the leg.

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908. SITUATION FOUR

(a) The following conditions obtain:


(1) The distance to the track is more than 1000 yards.

(2) The target has not zigged in the last 2 minutes.

(b) Course of Action:

(See Plate XXIV). The target has not zigged in the last two minutes and, therefore may be expected to change course shortly. The submarine should close the track on a 60 to 90 track and wait for the next zig. After the target has zigged shoot on the best torpedo track obtainable.

(c) In this situation if the target is on a long lead it may be necessary to shoot before he has zigged. The rule here is that when the angle on the bow gets to 90 degrees commence shooting regardless of the time on the leg. When the angle on the bow is 90 degrees you have an optimum torpedo track so a zig while the torpedoes are running will do the least amount of harm.

909. PRECAUTIONS APPROACH AND ATTACK TACTICS

In all the foregoing situations the Approach Officer should:

(a) Attempt to keep a small silhouette to the nearest escort if such action is feasible and does not unreasonably jeopardize the chances of a successful attack.

(b) Be alert to detect course or speed changes of the escorts or target promptly.

(c) Carefully note torpedo run when nearing the firing point to avoid being "run down".

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(a) In general on the firing leg commence shooting before the target has been on the leg more than 4 minutes.

(e) Commence shooting when the angle on the bow gets to 90 degrees regardless of time on leg.

(f) In general do not attempt to maneuver when the range is less than one half of the critical range. It is usually too late.

(g) As a general rule, when using stadimeter or telemeter scale ranges, the submarine must maneuver during the attack phase to obtain a small gyro angle (30 degrees or less). This is a major consideration and the submarine must accept whatever torpedo track results from this course of action. However, such is not the case when radar ranges are available. With radar ranges the large gyro angle may be accepted and the submarine is then able to choose a course which will result in a favorable torpedo track. This advantage is most pronounced in Situation (3) where for a medium speed target the difference in torpedo track obtained between heading at the target or nearly so and coming around to lead the target seeking a small gyro angle is as high as 30 degrees. Another major advantage to the submarine when using radar ranges is that last minute maneuvers of the target do not necessitate the submarine maneuvering because whatever gyro angle presents itself may be accepted.

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CHAPTER 10

THEORY OF THE PERISCOPE APPROACH AND SONAR ATTACK

1000. BASIC THEORY

The delivery of an accurate torpedo attack based entirely upon information obtained from sonar has been under study by submarine officers for a number of years. The perfection of this type of attack has been hampered by its complexity and the quality of the sonar information available.

The technical advances in the field of anti-submarine warfare have placed added emphasis on the submarine sonar equipment and its tactical employment. Studies in the last five years indicate that with sonar equipment now available a submarine can deliver a successful sonar attack against surface vessels provided periscope observations can be made during the approach phase. This chapter will therefore be confined to the theory of the sonar attack since the approach has been amply covered in Chapter 9.

In order to compute a hitting torpedo gyro angle there are four values which must be known, namely, target course, target speed, range and bearing of the target. The conventional method of obtaining these values is by successive observations of the target's range and bearing.

Let us assume now that the submarine is submerged below periscope depth and cannot obtain a visual

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observation of the target. With equipment presently available the only one of the four unknown values available is the bearing of the target obtained by sonar. The range of the target can occasionally be obtained by sonar but is seldom available until just prior to firing. Since we cannot yet rely on our ability to obtain a sonar range our procedures must be based upon the assumption that it is not available. It is obvious that one mathematical equation containing four variables cannot be solved if only one of is known.

The question then is what information regarding the target's motion can we obtain, by processing, the values of target bearing available from sonar. There is only one answer to this question. By the use of sonar bearings alone we can obtain the true direction of the target's relative motion and nothing else. This fact should be clearly understood and constantly borne in mind by everyone studying the problems of the sonar approach and attack.

At the present time there is no way by which the direction of the target's relative motion can be obtained except by laborious hand plotting methods. Numerous charts and plotting methods have been devised from time to time to accomplish this. Of all those evaluated at the Submarine School the Bearing Rate plotting method and the Bearing Difference plotting method have proved the most expeditious with the

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latter the preferred method. There are several mechanical solutions under development of which, one, has been tested at sea, and appears to be very promising.

Detailed theoretical studies show that regardless of the manner in which the sonar bearings are processed there are two basic requirements which must be met. First a continuous source of bearings must be available (intermittent or random bearings are almost valueless), and second the bearing accuracies should be plus or minus .1 degrees with a maximum error or plus or minus .25 degrees. A study of the plotting methods in Chapter V will show that for any given solution of target relative motion the assumption is made that the submarine and the target are both on a steady course during the period for which a solution is made. Any change of course or speed of the submarine or target will superimpose upon the rate of change of bearing another rate which is accelerating or decelerating in a variable manner and will result in a condition of "no solution". It is for this reason also that it is said there is "no solution" of target relative motion for a target which it is steering a constant helm or course clock track. There is a mathematical solution by which the effect of own ships maneuvers can be removed from the computed bearing rates leaving only the rate caused by target motion. The solution requires an assumed range or

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target speed and is so laborious as to be impractical of solution by any but mechanical computers.

In any fire control problem we have what is known as a solution time or, as it is commonly called, a dead time. This is the time which must elapse between the moment that the initial data is obtained and a solution is available. Let us assume that the target has been proceeding on some course which we know and that at problem time 12 minutes the target makes a course change of 40 degrees. It will take the target about 40 seconds to effect this change of course. During this period as explained there is no solution available so that the first possible useful data is not available until 12:40. Assuming that the Fire Control Party has detected the course change at 12:30 (which is not always the case) they will be ready to start a new solution at 12:40. It takes a minimum of two minutes using the Bearing Rate Plot to obtain the three points necessary to establish the target's relative course and a minimum of 1 1/2 minutes using the Bearing Difference Plot. The time is now 14:40 or 14:10. Allowing time to convert this relative course to true course the time will be 15:00 or 14:30. This dead time of 2 1/2 to 3 minutes for the solution of the new target's course is about the optimum and should be constantly borne in mine by the Approach Officer. This dead time will repeat itself should it be necessary to start a new solution because of changes of submarine course and speed or temporary

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loss of contact with the target.

Since we are assuming that the submarine will conduct a periscope approach and obtain a correct value of target speed and a range and bearing of the target before going to deep submergence the following fire control procedure will enable the Approach Officer to deliver an attack:

(a) Be certain that both the Nav Plot and the TDC and Sonar Plot are using the same value of target speed.

(b) Plot the last observation of range and bearing obtained. Advance the target at one minute intervals on the target course determined at last observation.

(c) When sonar bearings or Sonar Operator, or both indicate that target has changed course the TDC Operator changes target course 30 degrees in the indicated direction and announces to Nav and Sonar Plot time of zig.

(d) Sonar Plot commences solution for new target course.

(e) Nav Plot lays out TDC course from zig time indicated and gives TDC predicted range of target. TDC then uses this range as correct target range.

(f) When Sonar Plot obtains relative course he compare this with target speed and own course and speed on the maneuvering board to obtain true course. TDC Operator put this in TDC and Nav Plot repeats step (e).

(g) If Sonar Plot and Nav Plot solutions are correct

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the observed and generated sonar bearings should be in agreement.

It is highly important that each correction of target course put into the TDC be furnished the Nav Plot and that he in turn furnish the TDC a corrected range since observed and generated sonar bearings will not be in agreement unless both course and range are correct. At or close to the firing point a "ping range" may used as a check.

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CHAPTER 11

SUBMERGED APPROACH AND SONAR ATTACK TACTICS AGAINST

SURFACE TARGETS

1100. TACTICS

The tactics to be employed in the approach when a sonar attack is anticipated are the same as those outlined in Chapter 9, except that every possible effort should be made to place the submarine ahead of the target at a range between 6000 and 7000 yards. This will insure that succeeding course changes on the part of the target will require the minimum of maneuvering on the part of the submarine to deliver a successful attack. Special emphasis should be placed on the internal routine of the submarine to insure that all evolutions such as flooding tubes, charging impulse bottles, moving skids, etc., are accomplished prior to submerging below periscope depth. Failure to do this may result in loss of sonar contact at a critical time during the attack.

(a) Once the submarine has gone below periscope depth the Approach Officer must make every effort to avoid changes in course end speed. Should it, however, become necessary it should be done with the full realization that contact may be lost with the target and even though contact is maintained the Sonar Plot will be unable to track the target.

(b) Since it is highly desirable to avoid maneuvering the doctrine of the attack phase for the periscope

11-1


CONFIDENTIALSLM 1

approach will not apply and the Approach Officer must accept the best combination of torpedo track angle and gyro angle and range which presents itself. It should be borne in mind that errors in range will have less effect, when using large gyro angles, when the torpedo run is between 2000 and 2500 yards than between 1000 and 1500 yards.

11-2


Four drawings showing attack geometry described in the text.
Drawing showing a view through the periscope with graticule used to calculate masthead height.
Mast height and range slide rule described in the text.
Photo of stadimeter on the bottom of the periscope.

Photo of slide rule in position described in the text.
Periscope Radar Plot described in the text.

Stadimeter Plot described in the text.
Radar Tracking Plot described in the text.
Bearing Rate Plot on a maneuvering board described in the text.

Bearing Rat Plot Recorder's Form filled in as  described in the text.
Bearing Difference Plot as described in the text.

Bearing Difference as described in the text.

CONFIDENTIALSLM 1

BEARING DIFFERENCE PLOT DATA

Time Bearing Diff. Time Bearing Diff.
0-00 0-00 5-40 5-15
0-30 0-15 5-52 5-30
0-55 0-30 6-10 6-00
1-15 0-45 6-15 6-15
1-35 1-00 6-17 6-30
1-55 1-15 6-20 7-00
2-15 1-30 6-23 7-15
2-35 1-45 6-28 7-30
2-55 2-00 6-30 7-45
3-05 2-15 Submarine Course 000T
3-25 2-30 Submarine Speed 3 kts
3-40 2-45 Actual Target Course 170 degrees T
3-55 3-00 Target Speed 16 kts.
4-07 3-15 Initial Bearing 000 degrees T increasing
4-20 3-30 Reference Bearing 180 degrees T
4-35 3-45 Relative Motion Slope 8 degrees
4-50 4-00 True Direction of relative
5-00 4-15 motion 180-8 = 172 degrees T
5-10 4-30 Solved Target Course 171 degrees T
5-20 4-45 Target Zig to 130 degrees T at 6 minutes
5-30 5-00

NOTE: First plotted point on Plate XI is at 1-15 as preceding points are off diagram.

PLATE XIII


CONFIDENTIALSLM 1

BEARING REFERENCE PLOT DATA

Time Bearing Diff. Time Bearing Diff.
0-00 0-00 1-06 5-15
0-04 0-15 1-09 5-30
0-07 0-30 1-12 5-45
0-10 0-45 1-14 6-00
0-14 1-00 1-20 6-30
0-17 1-15 1-25 7-00
0-20 1-30 1-31 7-30
0-23 1-45 1-37 8-00
0-26 2-00 1-42 8-30
0-29 2-15
0-33 2-30 Submarine Course 000 degrees T
0-36 2-45 Submarine Speed 3 kts.
0-39 3-00 Actual Target Course 130 degrees T
0-42 3-15 Target Speed 16 kts.
0-45 3-30 Initial Bearing 010 degrees T increasing
0-48 3-45 Reference Bearing 190 degrees T
0-51 4-00 Relative Motion Slope 50 degrees
0-54 4-15 True direction of relative
0-58 4-30 motion 190-50 = 140 degrees T
1-00 4-45 Solved Target Course 132 degrees T
1-03 5-00

PLATE XIV


Divergent and Longitudinal spread diagrams as described in the text.
St=(So SIN LA/SIN Ab) target lead angle geometry as described in the text.
Deflection angle vs track angle curves as described in the text.

Deflection angle vs track angle curves as described in the text.

Submerged Approach and Attack Doctrine flow chart.

Target and OSC Situation I, first course of action, plotted as described in the text.
Target and OSC Situation I, second course of action, plotted as described in the text.
Target and OSC Situation II plotted as described in the text.
Target and OSC Situation III plotted as described in the text.
Target and OSC Situation IV plotted as described in the text.
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