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Depth Charges, Mark 6, Mark 6 Mod. 1, Mark 7, Mark 7, Mod. 1, OP 747, 1943, covers the U.S.N. depth charge from the first half of WW II.

We thank Ed Zajkowski for his generous loan of the original document used to create this online version.

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RESTRICTED
ORDNANCE PAMPHLET 747
(FIRST REVISION)
Depth Charges, Mark 6, Mark 6 Mod. 1, Mark 7, Mark 7, Mod. 1
Operating and Maintenance Instructions
A BUREAU OF ORDNANCE PUBLICATION
Issued December, 1943

 

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RESTRICTED ORDNANCE PAMPHLET No. 747

(FIRST REVISION)

DEPTH CHARGES
MARK 6
MARK 6, MOD. 1
MARK 1
MARK 1, MOD. 1

OPERATING AND MAINTENANCE INSTRUCTIONS

Department of the Navy
Bureau of Ordnance
Department of the Navy Bureau of Ordnance

22 DECEMBER, 1943


This publication is RESTRICTED and will be handled in accordance with Article 76 United States Navy Regulations 1920
 

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Department of Navy
Bureau of Ordnance

 

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NAVY DEPARTMENT
BUREAU OF ORDNANCE
WASHINGTON, D. C.

RESTRICTED 22 December 1943

ORDNANCE PAMPHLET NO. 747, FIRST REVISION

DEPTH CHARGES, MARK 6, MARK 6 MOD. 1, MARK 7 AND MARK 7 MOD. 1.

1. Ordnance Pamphlet No. 747, First Revision, contains a description and instructions for use of the Mark 6, Mark 6 Mod. 1, Mark 7 and Mark 7 Mod. 1 Depth Charges, with OCL M32-44 and OTI M2-44

2. This publication supersedes Ordnance Pamphlet No. 747 and its supplement, Ordnance Technical Instructions Numbers M2-43 and M6-43, Ordnance Circular Letters Numbers X-677, X-679, X-680, M10-42, M2-43, M4-43 and M11-43, and M23-43 and will become effective upon receipt. The latter publications should be destroyed.

3. This publication is RESTRICTED and is to be handled in accordance with the provisions of Article 76, U. S. Navy Regulations, 1920.

4. It is not intended that this publication be carried in aircraft for use therein.

G.F. Hussey, Jr.
Rear Admiral, U.S. Navy
Chief of Bureau of Ordnance

 

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CONTENTS O.P. NO. 747

Changes 1, pages 68a - 68w-3
Changes 2, page 97, figures 1-4
Changes 3, page 68, figure 1
Changes 4, page 3, page 68(c), par 12(c), (Change 1), page 90, figure 1

Page
PART I - CHAP. I
SUMMARY AND EXPLANATION 7
What they are 7
How they work 10
Safety features 10
CHAP. II
PARTS 17
Weights of Depth Charge Parts 17 Cases 21
Pistols 23
  How They Work 26
Mark 6 Pistol 31
  Parts- 33
  Depth controlling parts 33
  Parts inside casing 34
  Depth Setting Sleeve 36
  Guide Tube 38
  Locking Balls 38
  Inlet Valve 40
  Depth Settings 41
  Index Pointer 43
  Important Safety Devices 43
  Safety Wrench Stop 44
  Safe Setting Lock 45
Mark 6 Mod. 1 Pistol 46
  Depth Setting Mechanism 46
  Cylindrical Chamber 48
  Spring Adjusting Screw 48
  Valve Stem Hole 48
  Valve Seat 49
  Deep Firing Attachment 50
Index Pointer Plunger (Sticking) 52
  Booster Extenders 53
    How They Work 56
 
Page
Mark 6 Booster Extenders 60
  Parts 60
    Bellows 62
    Spindle 63
    Locking Balls 64
Mach. 6 Mod. 1 Booster Extender 65
Boosters 66
  Mark 6 66
  Mark 6 Mod. 1 67
  Mark 6 Mod. 2 68
Detonator Mark 1 Mod. 1 68
CHAP. III
STOWAGE AND HANDLING 69
  Cautions 73
  When Depth Charges Are Ready 73
    Cautions 75
  Depth Charge Upkeep Routine for Ships 76
    Pistol Routine-daily 77
    Pistol Routine-weekly 79
    Booster Extender Routine-daily 80
  Interchangeability of Parts 82
  Icing, Mark 6 Pistol & Booster Extender 83
    Anti-freeze Mixtures 83
    Introducing Mixtures 83
    Failures 85
    Sealing Substances 85
    Booster Extender Care 86
    Pistol Care 87
    In Port Instructions 87
    Ice Removal 88
 

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Page
CHAP, IV
SERVICE ASSEMBLY AND USE 89
TOOLS 89
  Original Service Set (Mark 6 Pistol) 89
  Packing Nut and Gland Wrench 89
  Screw Driver for Mark 6 Mod. 1 89
  New Service Sets 90
  Issuing Depots 90
Assembly Instructions 91
  Booster & Booster Extender 91
  Booster Extender Test 93
  Detonator 94
Loading Depth Charges into Tracks or Projectors 96
Removing, Changing, Safety Forks and Pistol Covers 97
Setting Depth on Pistols 99
Setting Mark 6 Pistol 99
Setting Mark 6 Mod. 1 Pistol 100
Launching Charges from Release Tracks 103
Throwing Charges from Projectors 103
Underwater Action 103
Sinking Rates of Charges 103
PART II-CHAP, V
INSPECTION AND TESTING 106
General Instructions 106
Testing Sets 107
Pistol Tests 107
Tests Mark 6 & Mark 6 Mod. 1 Pistols 109
  (with Mark 2 Mod. 1 set) 109
 
Page
Tests Mark 6, Mark 6 Mod. 1 113
  (with pistol testing fixtures) 115
Deep Firing Test Mark 6 Mod. 1 Pistol 117
Booster Extender Tests Mark 6 & Mark 6 Mod. 1 121
  (test set Mark 2 Mod. 1)
Case Inspection 123
Booster Can Inspection 127
Detonator Inspection 128
CHAP, VI
REPAIRING AND OVERHAULING 128-129
Pistols 126
  Causes of failure at 100 ft. setting 128
  Causes of failure at 500 ft. setting 131
  When failing to fire 132
  Calibration 132
  Mark 6 pistol calibration 132
  Mark 6 Mod. 1 Pistol Calibration 137
  Firing Plunger & Guide Tube Overhauling 141
  Pistol, complete overhaul 143
  Leaks, repairing 148
  Bellows, replacing 149
  Pistol reassembly 151
  Depth Assembly Mechanism Mark 6 Mod. 1 Pistol 159
  Frequency of Servicing 163
  Booster Extender Overhaul 165
  Disassembly 165
  Assembly 167
  Booster Cans, repairing 170
APPENDIX 171
  List of Ordnance Sketches and Drawings 171
DISTRIBUTION 173
 

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THE MARK 6 DEPTH CHARGE ASSEMBLED, with shadow of Mark 7 size around it.
THE MARK 6 DEPTH CHARGE ASSEMBLED
 

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PART I, CHAP. I O.P. NO. 747

SUMMARY AND EXPLANATION

WHAT THEY ARE

1 THE MARK 6 DEPTH CHARGE

1. THE MARK 6 depth charge consists of a 300 pound charge of TNT which is fired by a hydrostatically operated pistol through the usual detonator booster train. The Mark 6 pistol has a depth setting range of 30 to 300 feet.

2 THE MARK 6, MOD, 1

2. THE MARK 6 MOD. 1 depth charge is identical to the Mark 6 except that it is fitted with a Mark 6 Mod. 1 pistol which has a depth setting range of 30 to 600 feet.

3 THE MARK 7

3. THE MARK 7 charge is exactly the same as Mark 6 in all principal parts EXCEPT that it has a larger case and contains 600 pounds of TNT instead 300 pounds.

4 THE MARK 7, MOD, 1

4. THE MARK 7 MOD. 1 charge is the same as Mark 7 EXCEPT that it is fitted with the Mark 6 Mod. 1 pistol.

NOTE: The above identifications will apply no matter what booster extender mechanism, booster or other parts are used to make up the completed depth charge assembly.
 

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Depth charge cross section view.

 

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SUMMARY O.P. NO. 747

COMPONENTS OR PARTS

5. The above depth charges are made up of the following components:

(a) Case

(b) Charge

(c) Pistol

(d) Detonator

(e) Booster

(f) Booster Extender Mechanism

6. All of these charges measure 27.625 inches long. They DIFFER in weight and in diameter of case as follows:

(a) Mark 6 and Mark 6 Mod. 1 each weigh 420 pounds complete-and are 17.625 inches in diameter.

(b) Mark 7 and Mark 7 Mod. 1 each weigh 765 pounds complete-and are 24.875 inches in diameter.

HOW LAUNCHED

7. The Mark 6 and Mark 6 Mod. 1 charges can be dropped from all present types of U. S. Navy depth charge release tracks-and they can be fired from Mark 1 projectors (Y-Guns) and from Mark 6 or Mark 6 Mod. 1 projectors (K-Guns.)

8. The Mark 7 and Mark 7 Mod. 1 charges can be dropped from depth charge release tracks Mark 3, Mark 6, Mark 9 and Mods. They CANNOT be fired from types of projectors in service at this time.

 

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HOW THEY WORK O.P. NO. 747

FIRING AND SAFETY FEATURES

9. The depth charges are exploded at a predetermined depth by the hydrostatically operated pistol. The depth range depends upon the pistol used.

10. The chief safety feature for keeping charges from exploding until after they have entered the water, is the separation existing between the booster and detonator. Another safety feature is provided in the form of a pistol safe setting.

HOW THEY WORK

11. During shipment and stowage of a depth charge pistol, the inlet valve is closed by a plain safety cover screwed onto the valve body. When a charge is placed in a depth charge track this cover is replaced with one fitted with a projecting knob. The knob is broken off the cover by a wiping plate on the track when the charge is dropped, leaving an opening through which water can enter the pistol. If a charge is thrown from a projector, the plain cover is used. Before the projector is fired the plain cover must be removed by hand.

KNOBBED SAFETY COVER

Knobbed Safety Cover

 

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Cover Must Be Removed By Hand Prior To Projecting

PLAIN SAFETY COVER

12. Recently manufactured Mk. 6 pistols have nine possible settings of the index pointers, indicated by the figures 30, 50, 75, 100, 150, 200, 250, and 300 and the word SAFE stamped on the pistol flanges. The figures indicate the depths, in feet, beneath the surface at which a pistol will fire when the pointer is adjacent to any given setting. When a pistol is set at SAFE, it cannot fire if it has been properly assembled and calibrated.

13. As the charge sinks, water enters the pistol inlet valve at one end and the booster extender opening at the other

14. At a depth of 12 to 15 feet, hydrostatic pressure causes the booster extender to move the booster forward so that the detonator is housed in the booster can envelope. This action arms the depth charge which is now ready for firing.

15. A SAFE SETTING LOCK prevents the shock of gunfire, bomb hits, or underwater explosions from moving the index pointer off the SAFE setting. This lock consists of a short piece of No. 19 (".0358 dia.) copper wire rove through holes in lug of the index pointer and wrench stop. The ends of the wire are twisted together. The index pointer is thereby

 

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Launching from projector

LAUNCHING THE CHARGES

secured in the SAFE position and cannot be moved until the wire is broken. Round nose pliers, furnished in service tools sets, are used to install the wire. It is not necessary to remove the locking wire to change the index pointer from SAFE to a particular depth setting. The wire will be broken by the application of force to depth setting wrench handle. Whenever index pointer is reset to SAFE a new piece of wire is required. Wire, wound on a spool for convenient use, is included in service tool set. Modification of pistols in service and in store is covered by Ordalt No. 1735.

16. The depth at which the pistol fires is controlled by the setting of a pointer on the pistol. (Mark 6 pistol, 30 to 300 feet ; Mark 6 Mod. 1 pistol, 30 to 600 feet.)

 

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FROM RELEASE TRACKS
ENEMY SUBMARINE

 

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Cross section of depth charge with callouts at time of launch.

 

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Cross section of depth charge at time of detonation.

 

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Black indicates size of Mks 6 and Mk 6 Mod. 1
Red indicates comparative size of Mk 7 and Mk 7 Mod. 1

 

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