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Page 187 Continued
 

Section X
SIGHTING AND FIRE CONTROL EQUIPMENT

90. ARRANGEMENT OF SIGHTING AND FIRE CONTROL EQUIPMENT.

a. This section describes the on-carriage sighting and fire control equipment. It describes the operation, test, maintenance, and care and preservation of this equipment. Off-carriage parts, including Generating Unit M5, the Director M5A2, M5A1, or M5, the Cable System M8, Gunner's Quadrant M1 or M1918, and cable repair kit, are covered in other Technical Manuals (sec. XV).

NOTE: The arrangement of the azimuth and elevation mechanisms of this weapon is opposite from the usual arrangement of these mechanisms on other artillery weapons in that the azimuth mechanism is on the right side and the elevation mechanism is on the left side.

b. The fire control equipment is designed to operate as a coordinated system under the conditions encountered in short range antiaircraft fire on fast moving targets. In the event that the fire control equipment, or any part of it, is unavailable or disabled, emergency sighting equipment is provided.

c. The sighting equipment includes the Computing Sight M7 or M7A1, Sighting System M3, and bore sights.

(1) The elevation and azimuth operators sight through the rear and front open sights of the Sighting System M3 to track the target and to set in the necessary lead.

(2) The elevation and azimuth trackers follow the target through telescopes of the Computing Sight M7 or M7A1. Vertical and lateral deflections are mechanically set into the telescopes by a mechanism which is subject to adjustment by a sight setter who stands behind the azimuth tracker.

(3) Bore sights and a gunner's quadrant are provided for use in performing bore sighting adjustments and in orienting.

d. Gun pointing data originate at the AA Director M5A2, M5A1, or M5. The director determines the target position in space from the angular position of two tracking telescopes with which the operators



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Figure 160 - Signalling and Fire Control Equipment
Figure 160 - Signaling and Fire Control Equipment


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follow (track) their target. One telescope gives the horizontal position or azimuth; the other, the vertical angle or elevation. Ranges are estimated by the range setter at the director and may be adjusted quickly from observation of the tracer stream during fire. Smooth and accurate tracking at high angular rates of travel is made possible by use of a system of tracking known as aided tracking. The director produces firing azimuth and quadrant elevation data for transmission to the gun.

NOTE: The Director M5A2 will supersede Directors M5 and M5A1.

e. The Remote Control System M5 points the gun in azimuth and elevation according to the controlling data furnished from the director. The system includes electrical and hydraulic power equipment (oil gears) mounted on the carriage and connected to the traversing and elevating mechanisms.

f. Electric power to operate the director and power mechanisms for remote control is supplied by a gasoline-electric a-c Generating Unit M5.

91. DIRECT FIRE SIGHTS.

a. Guns in service are equipped with two types of direct fire sights. Guns not equipped with the Computing Sight M7 or M7A1 are equipped with Sighting System M3 (fig. 161). Guns equipped with the Computing Sight M7 are also provided with direct fire sights for emergency use and for bore sighting operations (fig. 163).

b. Sighting System M3, Guns Not Equipped With Computing Sight M7.

(1) These sights (fig. 161) are used when the director is not available. They provide a simple means of giving the necessary lead to allow for target travel during the time of flight of the shell, and of changing the lead quickly during the engagement owing to the change of position of the target.

(2) A "wheel" type front sight is used for elevation, and a "gate" type front sight is used for azimuth. The wheel type of sight has a clock face on which the course of the target is interpreted in terms of a clock hour. The gate type has vertical bars which are spaced in terms of degrees.

(3) The rear elevation sight has an adjusting lever for raising and lowering the line of sight.

(4) The front elevation sight and the front azimuth sight are mounted on slides which permit lateral adjustment. Each slide is secured by two wing nuts.

(5) When using these sights, the traversing and elevating hand cranks must be engaged (pushed in) and the oil gears of the remote control system must be disengaged. To disengage the azimuth oil



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Figure 161 - Sighting Systems M3 - Gun Not Equipped With Computing Sight M7 or M7A1
Figure 161 - Sighting Systems M3 - Gun Not Equipped With Computing Sight M7 or M7A1


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gear, disengage the power synchronizing mechanism by pulling the power synchronizing handle upward. This shuts off power to the oil gear and disengages the azimuth oil gear clutch. To disengage the elevation oil gear, move the elevation limit switch to the "OFF" position, disconnecting power to the elevation oil gear. Then disengage the elevation oil gear clutch lever by lifting the clutch lever lock and moving the clutch lever to the disengaged position (the top of the clutch lever toward the output coupling).

(6) Leads are set by tracking the target at different points on the front sight cross wires, in accordance with the practice of the using arms.

(7) The sights are ruggedly constructed, but because of their exposed position, must be protected against damage by bending. The sights should not be used as handholds or supports. Keep wing nuts securely tightened. Keep the cam surface under the elevation adjusting lever clean.

c. Direct Fire Sights, Guns Equipped With Computing Sight M7 or M7A1.

(1) These sights (fig. 163) are for use when neither the director nor Computing Sight M7 or M7A1 is available or in operating condition. They provide a simple means of estimating the necessary lead to allow for target travel during the time of flight of the shell.

(2) The rear sights (B, fig. 163) on both the azimuth and elevation sides of the gun are subject to adjustment for bore sighting. Vertical adjustment is accomplished by raising or lowering the peep rings in their holders. Elongated holes in the base of the holders provide means of making lateral adjustments.

(3) The front sights (A, fig. 163) on both the azimuth and elevation sides of the gun are of the "speed ring" type; permitting the course of the target to be interpreted in terms of a clock hour.

(4) When in use, the front sights are secured in their slides by two wing nuts.

(5) When using these sights, the traversing and elevating hand cranks must be engaged (pushed in) and the oil gears of the remote control system must be disengaged. To disengage the azimuth oil gear, disengage the power synchronizing mechanism by pulling the power synchronizing handle upward. This shuts off power to the oil gear and disengages the azimuth oil gear clutch. To disengage the elevation oil gear, move the elevation limit switch to the "OFF" position, disconnecting power to the elevation oil gear. Then disengage the elevation oil gear clutch lever by lifting the clutch lever lock and moving the clutch lever to the disengaged position (the top of the clutch lever toward the output coupling).

(6) Leads are set by tracking the target at different points on the front sight cross wires, in accordance with the practice of the using arms. The outer ring is equivalent to a target speed (in a plane at



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right angles to the axis of the bore of the gun) of 300 miles per hour; the middle ring, 200 miles an hour; the inner ring, 100 miles per hour; and the small vertical wires on the horizontal ("9 o'clock-3 o'clock") cross wire, 20 miles per hour. The vertical distance between the "9 o'clock-3 o'clock" wire and the small horizontal wire on "12 o'clock" is equivalent to superelevation for normal range. For very close ranges, therefore, the target should be sighted on this small wire, thereby removing superelevation. This wire is also used when bore sighting these sights.

(7) The front sights should not be mounted when Computing Sight M7 or M7A1 is in operating condition (fig. 163). When mounting them, be sure that the slides and stop surfaces are clean. Push the front sights down firmly against their stops and then securely tighten the wing nuts.

92. COMPUTING SIGHTS M7 AND M7A1.

a. General.

(1) This sighting system (figs. 162, 163, and 164) provides automatic correction of lateral and vertical deflection of its telescopes (M7 on the azimuth side and M74 on the elevation side) as the gun is moved in azimuth and elevation. Initial settings for course and speed of target, and subsequent adjustments thereof, are made by hand. The M7 and M7A1 Sights have been designed primarily for antiaircraft use but are equally effective in establishing leads on relatively slower moving ground targets.

(2) The Computing Sight M7A1 is exactly the same as the Computing Sight M7, except that the M7 model has a larger azimuth gear box handwheel. In addition, a different method of bore sighting and adjusting of the vertical axis of the deflection mechanism control case is necessary, due to a slight change in the link connecting the superelevation cam shaft arm to the trunnion frame.

b. Description.

(1) The telescope supporting assembly is bolted to the upper surface of the forward end of the breech casing. On the azimuth side of this assembly are the mechanisms which provide proper vertical and lateral deflections, including superelevation. Deflections given the azimuth telescope (fig. 162) are imparted to the elevation telescope (D) by a system of links and torque rods, the latter passing through the main support bar (E). Orientation of the direction of lead indicating arrow (H) is maintained as the gun is turned in azimuth by a drive through a flexible shaft (F) from the azimuth handwheel gearbox to the deflection mechanism of the main assembly. The link (0) from the superelevation cam shaft arm to the stud on the gun trunnion frame maintains the deflection mechanism control case (J) level at all elevations of the gun, and automatically



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Figure 162 - Computing Sight M7 Ready for Use With Telescope M7 (Azimuth - Right) and M74 (Elevation - Left) in Their Holders
Figure 162 - Computing Sight M7 Ready for Use With Telescope M7 (Azimuth - Right) and M74 (Elevation - Left) in Their Holders


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Figure 163 - Direct Fire Sights Mounted on Computing Sight M7 Main Assembly
Figure 163 - Direct Fire Sights Mounted on Computing Sight M7 Main Assembly


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causes adjustment of superelevation and lead as the gun moves in elevation.

(2) Direction of lead is indicated by the arrow mounted on the top of the deflection mechanism control case. The direction of the arrow, and thus of the lead, may be adjusted by turning the arrow itself or by turning the handwheel (G) on the azimuth gearbox to which the lower end of the flexible shaft is attached. The arrow and handwheel rotate in the same direction relative to the gun, but opposite to the direction of the traverse, thereby maintaining orientation of the arrow with respect to the target path.

(3) Adjustment for speed of the target is made by turning the spoked wheel (I) mounted on the face of the deflection mechanism control case. The figures on the dial show the level flight speed set into the mechanism.

(4) Effects of change in the speed setting and in the direction of the arrow with respect to the gun are conveyed to the telescope deflection system by the telescoping shaft attached to the swivel extending from the lead screw housing (K) on the undersurface of the deflection mechanism control case.

(5) Computing Sights M7 and M7A1 mount two Tracking Telescopes, M7 on the azimuth side and M74 on the elevation side, which are identical except for difference of reticle.

(a) Both are erecting telescopes with the following optical characteristics:

Power 1 x
Field of view 11 deg
Diameter of exit pupil 0.6 in.
Eye distance 4.384 in.

(b) Each telescope is clamped in a holder from which it is readily removed for traveling. Each holder has a locating projection to insure correct vertical and horizontal positioning of the reticle lines.

(c) The Telescope M7 (C, in fig. 162) is so mounted on the azimuth side as to show a solid vertical line and a broken horizontal line of the reticle. The azimuth tracker keeps the vertical line on the target.

(d) The Telescope M74 (D, in fig. 162) is so mounted on the elevation side as to show several horizontal lines graduated to give the proper superelevation of the gun when used against land targets at various ranges. For antiaircraft, the elevation tracker keeps the line marked "A-A" on the target.

(e) A dust cap, which consists of a leather cap for each end, connected by a strap, is provided for each telescope. One packing chest, furnished with padlock and keys, with compartments for both telescopes, is provided for each carriage.

(f) The lighting device provided for each telescope includes a metal tube containing two standard flashlight cells, a switch, and



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Figure 164 - Azimuth Side of Computing Sight M7 With Direct Fire Sight Mounted
Figure 164 - Azimuth Side of Computing Sight M7 With Direct Fire Sight Mounted


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a flexible cord with plug to fit in the lamp socket of the telescope holder. The metal tube fits into a sleeve on the arm of the sighting system.

c. Operation.

(1) Clamp the Telescopes M7 and M74 in their holders. In each case, the locating slot of the telescope is positioned so that the broken line is the line not required for tracking.

(2) When necessary, illuminate each reticle by closing the switch in the front end of the lighting device.

(3) Engage (push in) the traversing and elevating hand cranks.

(4) Disengage the oil gears by pulling up the azimuth oil gear clutch operating handle, throwing the elevation limit switch to "OFF" position, and disengaging the elevation oil gear clutch lever (move top of lever toward coupling), locking it by means of the auxiliary lever.

(5) As the azimuth and elevation trackers slew the gun toward a target, a sight setter (standing behind the azimuth tracker) turns the speed wheel (I) to what he estimates to be the speed of the target (which registers on the dial) and turns the arrow about its vertical axis so that it lies in the slant plane containing the gun and the target path. (If the target path is level, the arrow shaft should be parallel with it. If the target is diving, the head of the arrow should point to the spot where the target path, if extended, would strike the ground (or horizontal plane). If the target is climbing, the head of the arrow should be pointed directly away from the spot where a rearward extension of the target path would intersect the horizontal ground plane.)

(6) The trackers aline their telescopes on the target and so track as to continue to maintain their respective cross hairs thereon.

(7) The sight setter observes the tracer stream and makes such adjustments of the arrow and speed setting as to pass the trajectory curve through the target.

d. Tracking Adjustments.

(1) ADJUSTING SPEED.

(a) If the arrow is positioned with respect to the target path (subpar. c (5), above), all shells will pass through the path of the target regardless of the speed setting. However, this "tracer cross" will not occur at the target (be a hit) unless the proper speed has been set into the sight. Note whether the tracer stream crosses the line of sight to the target between the gun and the target, or passes beyond the target and is momentarily blotted out by the target (fig. 165).

(b) If the tracer stream passes on the near side of the target; increase the speed setting.

(c) If the tracer stream passes on the far side of the target; reduce the speed setting.



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Figure 165 - Adjustment of Fire by Observation of the Tracer Stress
Figure 165 - Adjustment of Fire by Observation of the Tracer Stress



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(2) ADJUSTING SPEED FOR OTHER THAN HORIZONTAL FLIGHT. For other than horizontal flight, speed must be constantly changed during the course. In the case of a diving target, start with a lower than estimated speed for the incoming leg; increase to what is believed the correct speed just before the midpoint of the course, and then to an increasingly greater speed for the outgoing leg. In the case of a climbing target, start the incoming leg with a greater than estimated speed and then constantly decrease the speed setting, as indicated by the tracer stream.

(3) ADJUSTING DIRECTION OF LEAD INDICATING ARROW.

(a) If the course is subject to cross wind or the arrow is not correctly set, the tracer stream will not cross the line of sight to the target, but will seem either high or low with respect to the target as it passes the line of sight to the target (fig. 165).

(b) If the tracer is high with respect to the target, rotate the arrow so that its head moves away from the sight setter slightly. This can be done either by grasping and turning the arrow itself, or by rotating the handwheel in the opposite direction to the turn of the gun in azimuth (by speeding up the rotation of the handwheel).

(c) If the tracer is low with respect to the target, raise it by rotating the arrow so that its head moves toward the sight setter. This can be done by either grasping and turning the arrow itself, or by rotating the handwheel in the same direction as the turn of the gun in azimuth (by retarding the rotation of the handwheel).

(d) On directly incoming or outgoing courses, the tracer stream may be shifted to the left by moving the head of the arrow to the left, and to the right by moving the head of the arrow to the right.

(e) Note that if the arrow is observed from below and to the rear as it is adjusted, the head of the arrow seems to rise slightly as it is rotated toward the sight setter. Thus, the tracer stream is shifted in the same direction as the head of the arrow for all conditions outlined in substeps (b), (c), and (d), above.

e. Disassembly and Assembly. Except for the installation and removal of the telescopes or the forward emergency direct fire sights incident to normal use, the only other assembly or disassembly operations performed by the using arms are those necessary to renew the lamps or dry cells of the lighting device.

(1) To replace the dry cells, grasp the cap at the forward end of the lighting device and pull it forward, removing the tube containing the dry cells from the cylindrical sleeve on the arm. Unscrew the tube and replace the dry cells, placing both cells with their central terminals toward the cap. Use two standard flashlight battery cells. Screw the tube into the cap and replace it in the sleeve on the arm.

(2) To replace a lamp, remove the plug on the flexible cord from the lamp socket; then unscrew the socket, rendering the lamp accessible.



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Figure 166 - Azimuth Side of Computing Sight M7 in Bore Sighting Position
Figure 166 - Azimuth Side of Computing Sight M7 in Bore Sighting Position


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Replace the lamp, using a standard screwbase flashlight lamp, and return the socket and plug to their original positions.

93. TESTS AND ADJUSTMENTS OF COMPUTING SIGHTS M7 AND M7A1.

a. General. The alinement of the sighting system should be verified frequently and adjusted if necessary.

b. Alinement of Telescopes. The optical axis of the telescopes are alined parallel with each other and with the bore of the gun when superelevation and all deflections are removed from the sight as explained in step (1), below, for the Computing Sight M7, and in step (2), below, for the Computing Sight M7A1.

(1) ALINEMENT OF TELESCOPES, COMPUTING SIGHT M7.

(a) Place the bore sights in the gun.

(b) Remove the wing screw which connects the link from the trunnion to the superelevation cam shaft arm.

(c) Tip the deflection mechanism control case forward by rotating the superelevation cam shaft arm.

(d) Remove the bore sighting plug from its clip and insert it in the hole in the superelevation cam arm, alining this hole with the hole in the superelevation cam link. See figure 166 of the sight in the bore sighting position.

(e) Set the speed to zero by turning the speed control handwheel.

(f) Bore sight the gun on a celestial body or other distant object.

(g) Adjust the telescope holders laterally or vertically as necessary to bring the center of the vertical line of the Azimuth Telescope M7 and the center of the "A-A" line of the Elevation Telescope M74, to on target position.

(h) Pull out the bore sighting plug and place it back in its clip. Tip the deflection mechanism control case into its normal vertical position and connect the link from the trunnion to the superelevation cam arm with its wing screw.

(2) ALINEMENT OF TELESCOPE, COMPUTING SIGHT M7A1.

(a) Place the bore sights in the gun.

(b) Remove the wing screw which locks the superelevation cam arm and the superelevation arm yoke together.

(c) Tip the deflection mechanism control case forward by rotating the superelevation cam shaft arm.

(d) Remove the bore sighting plug from its clip and insert it in the hole in the superelevation cam arm, alining this hole with the hole in the superelevation cam link. See figure 166 of the sight in the bore sighting position.

(e) Set the speed to zero by turning the speed control handwheel.

(f) Bore sight the gun on a celestial body or other distant object.

(g) Adjust the telescope holders laterally or vertically as necessary



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to bring the center of the vertical line of the azimuth Telescope M7 and the center of the "A-A" line of the elevation Telescope M74 to on target position.

(h) Pull out the bore sighting plug and place it back in its clip. Tip the deflection mechanism control case into its normal vertical position and replace the wing screw which locks the superelevation cam arm and the superelevation cam arm yoke together.

c. Verification and Adjustment of the Vertical Axis of Deflection Mechanism, Computing Sight M7.

(1) Level the gun carriage.

(2) Bring the gun tube to zero degree elevation.

(3) Place a gunner's quadrant set to zero on the milled surfaces of the deflection mechanism control housing using parallel bar part No. 7578746.

(4) Adjust the length of the link between the superelevation cam arm and the trunnion until the deflection mechanism control housing is accurately leveled as shown by the gunner's quadrant.

(5) Elevate the gun to 0 degree -15 degrees -30 degrees -45 degrees -60 degrees -75 degrees. The deflection mechanism control housing should remain level within ±2 mils. If the deflection mechanism control housing does not remain level within ±2 mils, perform the adjustments as indicated below.

(6) If the deflection mechanism control housing tips forward or backward more than 2 mils when performing the check in step (5), above, it may be corrected in the following manner:

(a) If the deflection mechanism control housing tips forward, it means that the pivot at the trunnion is either too low and the link between the trunnion and the superelevation cam arm is slightly too long, and or too far back and the link is too long by an equal amount. In order to correct the first of these conditions, move the pivot up in small steps by its eccentric and shorten the link slightly. Check at 0 degree -15 degrees -30 degrees -45 degrees -60 degrees -75 degrees after each adjustment. If this does not correct the error, correct for the second condition. In order to correct for the second condition, move the pivot forward in small steps by its eccentric and shorten the link in equal steps. Check after each adjustment of 0 degree -15 degrees -30 degrees -45 degrees -60 degrees -75 degrees.

(b) If the deflection mechanism control housing tips backward, it means that the pivot is either too high and the link is slightly too long, and or too far forward and the link is too short by an equal amount. In order to correct this first condition, lower the pivot in small steps by its eccentric and shorten the link slightly. Check after each adjustment of 0 degree -15 degrees -30 degrees -45 degrees -60 degrees -75 degrees. If this does not correct the error, correct for



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the second condition. In order to correct this second condition, move the pivot back in small steps by its eccentric and lengthen the link in equal amounts. Check after each adjustment of 0 degree -15 degrees -30 degrees -45 degrees -60 degrees -75 degrees.

(c) When the above adjustments have been made, make certain all nuts, screws, and bolts used in making the adjustments are secure.

d. Verification and Adjustment of the Vertical Axis of Deflection Mechanism-Computing Sight M7A1.

(1) Level the gun carriage.

(2) Bring the gun tube to zero degree elevation.

(3) Place a gunner's quadrant set to zero on the milled surfaces of the deflection mechanism control housing using parallel bar, Part No. 7578746.

(4) Adjust the length of the link between the superelevation cam arm and the trunnion until the deflection mechanism control housing is accurately leveled as shown by the gunner's quadrant.

(5) Elevate the gun to 0 degree -15 degrees -30 degrees -45 degrees -60 degrees -75 degrees. The deflection mechanism control housing should remain level within ±-2 mils. If the deflection mechanism control housing does not remain level within ±2 mils, perform the adjustments as indicated below.

(6) If the deflection mechanism control housing tips forward or backward more than 2 mils when performing the check in step (5), above, it may be corrected in the following manner:

(a) If the deflection mechanism tips forward, it means that the link pivot on the superelevation cam arm is either too high and the link connecting the superelevation cam arm to the trunnion is slightly too long, and/or too far toward the rear of the gun and the link is too short by an equal amount. In order to correct the first of these conditions, move the pivot down by means of its eccentric in small steps and shorten the link slightly. Check at 0 degree -15 degrees -30 degrees -45 degrees -60 degrees -75 degrees after each adjustment. If this does not correct the error, correct for the second condition. In order to correct for the second condition, move the pivot forward in small steps by means of its eccentric and lengthen the rod by equal amounts. Check at 0 degree -15 degrees -30 degrees -45 degrees -60 degrees -75 degrees after each adjustment.

(b) If the deflection mechanism tips backwards, it means that the pivot is either too low and the link is slightly too long and, or too far forward and the rod is too long by an equal amount. In order to correct for the first of these conditions, move the pivot up in small steps by its eccentric and shorten the link slightly. Check after each adjustment of 0 degree -15 degrees -30 degrees -45 degrees -60 degrees -75 degrees. If this does not correct the error, correct for



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the second condition. In order to correct for the second condition, move the pivot back in small steps by means of its eccentric and shorten the link in equal amounts. Check over each adjustment at 0 degree -15 degrees -30 degrees -45 degrees -60 degrees -75 degrees.

(c) When the above adjustments have been made, make certain all nuts, screws, and bolts used in making the adjustments are secure.

e. Verification of Alinement of Main Assembly With Bore.

(1) Level the gun carriage.

(2) Level the gun to zero elevation, using a gunner's quadrant set at "0."

(3) Test level of the main bracket on the azimuth side by putting the gunner's quadrant across its two bosses. If there is a deviation of over 5 mils above or below zero elevation, report to the responsible ordnance unit.

f. Verification of Azimuth Drive to Arrow.

(1) Level the gun carriage.

(2) Level gun to approximately zero elevation and aline bore and axis of arrow shaft with a distant object.

(3) Set speed to 500 miles.

(4) Traverse gun through 360 degrees. If axis of arrow does not remain directed at the same object, report to the responsible ordnance unit.

94. CARE AND PRESERVATION, COMPUTING SIGHTS M7 AND M7A1.

a. General Precautions.

(1) Disassembly and assembly by the using arms is permitted only to the extent specifically authorized herein. Turning of screws or other parts not incident to bore sighting, alinement of telescopes, or to the use of the system is expressly forbidden.

(2) Keep the system clean and in condition for traveling when not in use, the telescopes in their cases and the canvas covers in place.

b. Lubrication.

(1) Ball bearings, gear drives, covered joints and the flexible shaft are lubricated at assembly. Further lubrication of these will be required only at long intervals, and is performed by ordnance personnel.

(2) Telescope yoke surfaces, the telescoping rod to the azimuth telescope yoke, and link clevis pins should be frequently oiled with OIL, lubricating, for aircraft instruments and machine guns.

(3) Keep the outside of the flexible shaft casing free of oil.

c. Lighting Devices. Remove the flashlight battery cells whenever the lighting devices are not in use for several days. Chemical



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reaction set up in the cells as they become exhausted will cause the cells to swell, thereby making removal difficult and damaging the battery tube.

d. Telescopes.

(1) To obtain satisfactory vision, it is necessary that the exposed surfaces of the lenses be kept clean and dry. Corrosion and etching of the surface of the glass which greatly interfere with the good optical qualities of the instrument can be prevented or greatly retarded by keeping the glass clean and dry.

(2) Under no conditions should polishing liquid, paste, or abrasives be used for polishing lenses.

(3) For wiping optical parts, use only PAPER, lens, tissue. Use of cleaning cloth on optical glass is not permitted. To remove dust, brush the glass lightly with a clean, camel's-hair brush and rap the brush against a hard body to knock out the small particles of dust that cling to the hairs. Repeat this operation until all dust is removed.

(4) Exercise particular care to keep the lens free from all grease. Do not wipe the lens with the fingers. To remove a slight amount of grease from the lenses, breathe heavily on the glass and wipe off with PAPER, lens, tissue; repeat this operation several times until clean. If inspection reveals that the internal optics are dirty or greasy, the telescopes must be turned over to the nearest ordnance unit.

(5) Moisture due to condensation may collect on the optical parts of the telescopes when the temperature of the parts is lower than that of the surrounding air. This moisture, if not excessive, can be removed by warming the telescopes in a warm place. Heat from strongly concentrated sources should never be applied directly, as it may cause unequal expansion of parts, resulting in breakage of lens, or inaccuracies in observation.

95. BORE SIGHT.

a. General. The bore sight is used to indicate the direction of the axis of the bore of the gun, for alinement and verification of sights. Each bore sight is composed of a breech element and muzzle element.

b. Description.

(1) The breech bore sight is a hollow cylinder with one end closed except for a small aperture. This sight fits accurately into the breech chamber of the gun.

(2) The muzzle bore sight consists of a tube with an extension at one end retained by a chain (to which is attached a disk with an aperture near the outer edge) and at the other end of the tube two cross bars are welded.

c. Operation.

(1) Remove the section of the cartridge case deflector which is



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Figure 167 - Remote Control System M5 - On-carriage Components
Figure 167 - Remote Control System M5 - On-carriage Components

attached to the rear of the breech casing. Place the breech bore sight in the breech opening. Attach the muzzle bore sight.

(2) Look through the aperture in the breech bore sight, the direction of the axis of the bore being indicated by the intersection of the cords at the muzzle.

96. DESCRIPTION OF REMOTE CONTROL SYSTEM M5.

a. General.

(1) The remote control system (fig. 167) is an electrically controlled hydraulic power system designed for use with the 40-mm Gun Carriages M2 and M2A1 (AA). It is controlled by the AA Director M5A2, M5A1, or M5. Power is supplied from the Generating Unit M5. The function of the remote control system as a whole is to point the gun accurately in azimuth and elevation according to the output data supplied from the AA director. This type of control is known as "remote gun control."

(2) To oil gear units, one for azimuth and one for elevation, supply controlled driving power for traversing and elevating the gun. The gun must be brought into approximate alinement with the director before the oil gear may be engaged but, once the oil gear is engaged, the gun will follow the director accurately. Approximate alinement of the gun with the director is shown by an azimuth indicator toward



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Figure 168 - Diagram Showing Routing of Cables on Gun Carriage
Figure 168 - Diagram Showing Routing of Cables on Gun Carriage


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Figure 169 - gun Junction Box
Figure 169 - gun Junction Box


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Figure 170 - 3-hole Recepticle and Matching Fingers of Cable Plug
Figure 170 - 3-hole Receptacle and Matching Fingers of Cable Plug


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Figure 171 - Cable System M8 - (15-foot Cable Not Shown)
Figure 171 - Cable System M8 - (15-foot Cable Not Shown)


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Figure 172 - Oil Gear-Remote Control System M5
Figure 172 - Oil Gear-Remote Control System M5



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Figure 173 - Elevation Limit Switch
Figure 173 - Elevation Limit Switch


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Figure 174 - Elevation Oil Gear Clutch Lever Showing Operation of Locking Lever
Figure 174 - Elevation Oil Gear Clutch Lever Showing Operation of Locking Lever



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Figure 175 - Lowering the Power Synchronizing Handle Turns ON Azimuth Power Switch and Engages Azimuth
Figure 175 - Lowering the Power Synchronizing Handle Turns "ON" Azimuth Power Switch and Engages Azimuth


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the rear of the loading platform near the power synchronizing mechanism.

(3) The system permits continuous tracking in azimuth, but is limited in elevation by an elevation limit switch which automatically goes to "OFF" before the mechanical limit stops are reached.

b. Cable Connections. The arrangement and approximate location of the principal on-carriage parts of the remote control system are shown in figure 167. The cable connections are shown in figure 168. Cable connections from the director and generating unit are made to the gun junction box (fig. 169). The cable from the director is 30 feet (or 60 feet) long, and the cables from the generating unit are 225 feet long and 15 feet long (Cable System M8, fig. 171), joined by the switch box. Electrical connections pass to the top carriage through the contact ring, which permits traversing the gun without kinking or twisting the external connecting cables.

c. Gun Junction Box. The gun junction box (fig. 169) is the unit to which the cables from the director and generating unit are connected. When not in use, a cover protects the receptacles. One receptacle has three holes marked "A," "B," and "C" to receive the generating unit cable (fig. 170). The fingers of the cable plug are correspondingly marked. The other receptacle accommodates the director cable which has a "D" plug with fifteen terminal rings (fig. 171).

d. Oil Gears. Two oil gear units are mounted on the carriage (fig. 167). The elevation oil gear is on the left side, and the azimuth oil gear is on the right side. Each oil gear (fig. 172) is a weather-tight assembly consisting of an electric motor at the top, then an electrical control unit and, at the bottom, an oil pump and oil motor in a single housing. The electric motor drives the oil pump through a chain drive which is inclosed in an oiltight housing. An arrow on the motor housing indicates the direction in which chain should turn. The electrical control unit operates a pilot valve (fig. 183) which controls the flow of oil from the oil pump to the oil motor.

e. Elevation Limit Switch.

(1) Power to the elevation oil gear is controlled by the elevation limit switch (fig. 173).

(2) When the switch is turned "ON" (B, fig. 173) the elevation oil gears are energized.

(3) When the switch is turned "OFF" (A, fig. 173) (either by hand or automatically), the elevation oil gear does not operate. The gun can be operated manually by engaging the hand cranks.

(4) When operating by remote control from the director, the elevation limit switch trips and is automatically turned "OFF" at the upper and lower limits of elevation.

(5) When the elevation limit switch cuts off automatically, it is



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Figure 176 - Azimuth Clutch Lever Disengaged by Blocking (For Adjustment Purposes Only)
Figure 176 - Azimuth Clutch Lever Disengaged by Blocking (For Adjustment Purposes Only)

necessary to engage the hand cranks, elevate or depress the gun slightly, and then turn "ON" the elevation limit switch by hand (B, fig. 173).

(6) The upper limit is normally fixed at 85 degrees, while the lower limit is fixed at a point depending upon the emplacement of the gun so that the line of fire is above any intervening obstruction. For adjustment of these limits, see paragraph 98 h.

f. Elevation Clutch Lever.

(1) The lower rear portion of the oil gear houses a clutch mechanism for disengaging or engaging the oil gear. The elevation oil gear clutch (fig. 174) is engaged or disengaged by hand. It has an auxiliary locking lever to lock the elevation clutch lever in the "IN" or "OUT" positions.

(2) Whenever it is desired to shift the clutch lever from the "IN" or "OUT" positions, the locking lever is lifted to unlock and enable the clutch lever to be shifted, and must be lowered to lock the clutch lever after it is shifted (A, fig. 174).

(3) The elevation oil gear is engaged ("IN") when the top of the lever is in the forward position (B, fig. 174). In this "IN" position, the elevation oil gear is using hydraulic pressure to elevate the gun automatically by remote control from the director.



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Figure 177 - Azimuth Indicator - Match-the-pointer Dial
Figure 177 - Azimuth Indicator - "Match-the-pointer" Dial
Figure 178 - Azimuth Indicator - Modified Red-black-white Dial
Figure 178 - Azimuth Indicator - Modified "Red-black-white" Dial

(4) The elevation oil gear is disengaged ("OUT") when the top of the clutch lever is in the rear position (C, fig. 174). In this "OUT" position, the gun is free from director remote control and is operated by the elevation handwheel at the gun.

CAUTION: The elevation limit switch must be "OFF" before engaging or disengaging elevation clutch.

g. Azimuth Clutch and Power Switch.

(1) The azimuth power switch is automatically turned "ON" when the power synchronizing ("SLEWING") handle is depressed. This energizes the azimuth oil gear.

(2) When this handle is depressed (fig. 175), the azimuth oil gear clutch is also automatically engaged ("IN"). The gun now operates on remote control from the director.

(3) When the power synchronizing handle is raised, the azimuth switch cuts "OFF" automatically, and the clutch is automatically thrown "OUT" (disengaged). The gun then does not operate by remote control and is slewed by hand.

(4) If it is desired to cut off the azimuth switch while the power synchronizing handle is depressed (for adjustment purposes), it is necessary to block the switch as illustrated in figure 176.

h. Azimuth Indicator.

(1) The azimuth indicator (figs. 177 and 178) is used as an alinement indicator when synchronizing the gun with the director, after slewing the top carriage.

(2) The "match-the-pointer" indicator (fig. 177) consists of a synchronous repeater, containing a circular black shutter with a white pointer which follows the rotation of the coarse azimuth transmitter



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Figure 179 - Diagram Illustrating Dead Sector
Figure 179 - Diagram Illustrating "Dead Sector"

in the director, and a mechanical dial with a white pointer which is geared to the traversing mechanism of the gun carriage.

(3) After the gun has been slewed by hand, its synchronization with the director is disturbed (it being either behind or ahead of the director). When the carriage is within 10 degrees of alinement with the director, the indicator shows this by means of two limit lines. Within these limits, the electrical system will automatically synchronize the gun and director without attention of the gun detail. If the gun is out of alinement by more than 10 degrees, the electrical system cannot synchronize the gun with the director and the gun will be "out of phase." The indicator shows this by the matching pointer being beyond the limit marks (fig. 177) and the gun must be slewed until the indexes match approximately.

(4) The "red-black-white" (blackout) indicator may be found in some guns. This indicator has red, black, and white sections in the dial. The matching position is indicated when the dial is "blacked out" (or almost blacked out). If the gun is out of phase with the director, either the red or the white markers will show. A narrow strip of red or white indicates satisfactory alinement.

(5) The majority of the "red-black-white" (blackout) indicators



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Figure 180 - Choosing a Reference Point
Figure 180 - Choosing a Reference Point

have been modified. The dials have been painted black except for the alining marks, one on the mechanical dial and one on the shutter (fig. 178). This change makes the indicator similar to the standard indicator.

(6) INDICATOR ADJUSTING KNOB. When the gun and director are alined, the indicator marks should match exactly. Otherwise, the indicator should be adjusted. Remove the adjusting knob cover (fig. 183), depress, and turn the knob until the "match-the-pointer" indicator marks match (fig. 177) or the "blackout dial" blacks out.

97. SETTING UP, ORIENTING, AND OPERATION, REMOTE CONTROL SYSTEM M5.

a. Initial Set-up. Before firing operations are started, the following steps should be taken:

(1) Level the gun carriage accurately. Instructions for leveling the gun carriage are contained in paragraph 37.

(2) Orient the director with the gun as instructed in paragraph 94 c.

(3) Connect the generating unit and director to the gun mount by the cables provided, making sure that all switches are "OFF" until cable connections have been completed. Turn the "D" plug of the director to lock the plug in its socket of the gun junction box (fig. 169). The plugs of the generating unit cable have a round nut which must be screwed to the body of the mating receptacle of the gun junction box.

(4) The main power switch is on the control panel of the generating unit. This switch should not be turned "ON" until the cables have been connected and the cable plugs secured.

b. Emplacing and Setting Up.

(1) Since there are no provisions for parallax corrections, and since in the prescribed method of fire adjustment it is necessary for the trackers to see tracers that cross the gun target line, emplace the director 13 to 15 feet from the pintle center of the gun. This results



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in a dead sector which extends about 35 degrees to either side of the director (fig. 179) in which the gun should ordinarily not be fired, to avoid injury to the director personnel.

(2) The elevation limit switch should be set to cut off automatically at a safe lower limit to clear any obstructions within the line of fire. This adjustment is made by loosening the two clamp nuts which are visible through the slot of the rotating trunnion plate (A, fig. 187) and shifting laterally the stops. If the trunnion plate does not have a slot to provide access to the nuts, the plate must be removed and adjustment then made (B, fig. 187).

c. Orienting.

(1) GENERAL.

(a) Orienting is the alining of the director and gun on a reference point in azimuth and elevation. This is necessary so that the gun will point in the direction indicated by the director (as illustrated in figure 180).

(b) A clearly defined object, preferably in the field of fire and more than 2,500 yards distant, should be selected as a reference point. If an object 2,500 yards distant cannot be obtained, a closer point may be used if it is approximately in line with the director and gun.

(c) Set up the gun and director according to subparagraph b, above.

(d) Level the gun and director.

(e) Be sure that all switches are off at the gun and at the director.

(f) Set zero deflection in the director by pushing in the rate setting clutch knob and turning the tracking handwheel until the white mark on the deflection gear is lined up with its index marker. Then disengage the rate setting clutch by pulling the knob out. Deflection will be zero in both azimuth and elevation.

(g) Connect the generator cable to the gun only, and turn on the master switch at the generator.

(h) Turn on the power to the azimuth oil gear by depressing the power synchronizing handle.

(i) Check the dither of the azimuth oil gear and adjust if necessary (par. 98 d).

(j) Adjust the azimuth oil gear to neutral (par. 98 e).

(k) Place bore sights on the gun.

(l) Turn on the power to the elevation oil gear by depressing the elevation limit switch. (Be sure the clutch is engaged.)

(m) Check the dither of the elevation oil gear and adjust if necessary (par. 98 (1).

(n) Adjust the elevation oil gear to neutral (par. 98 e).

(o) Shut off the power at the main power switch of the generator and connect the gun and director through the fifteen-conductor cable.



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Figure 181 - Making Azimuth Indicator Adjustment
Figure 181 - Making Azimuth Indicator Adjustment

(p) Turn on the master switch at the generator.

(2) ORIENTING IN AZIMUTH.

(a) Turn on the power at the director and gun (azimuth side only).

(b) Bore sight the gun on the previously selected orienting point, moving the gun by means of the director.

(c) Disengage the orienting clutch in the following manner:

1. Remove the orienting clutch cover.

2. Tighten the small locking nut.

NOTE: This step must be performed first; otherwise, the gun will move when the large knob is loosened.

3. Loosen the large knob.

4. Replace the orienting clutch cover.

(d) Traverse the director with the azimuth handwheel until the director telescopes are on the orienting point.

(e) Re-engage the orienting clutch by reversing the procedure given in step (c), above.

(f) Traverse the director several times and see if the gun and director aline on the orienting point.

(g) Observe the azimuth indicator. The two white markers should be alined (or the dial blacked out) (fig. 181).

(h) The gun is now oriented in azimuth.

(3) ORIENTING IN ELEVATION.

(a) Set the elevation dials of the director at a convenient reading, for example 45 degrees.



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(b) With the elevation limit switch off, elevate the gun manually to 45 degrees (to correspond to the reading on the director).

(c) Observe the elevation scale plate on the gun for a proper reading.

(d) Turn on the power to the elevation oil gear by depressing the elevation limit switch.

(e) Check the position of the gun with a gunner's quadrant.

(f) The gun should point at 45 degrees. If not, make adjustments on the resetter gear train of the elevation oil gear.

(g) Traverse the gun in elevation several times.

(h) Recheck the alinement of the gun and director at 45 degrees with the gunner's quadrant.

(i) The gun is oriented in elevation.

PRECAUTION: Be particularly careful when orienting in elevation that the elevation motor switch at the director is "OFF." Otherwise, a superelevation will be set in, and orienting will be in error by the amount of superelevation.

d. Tracking the Target.

(1) Turn on the main switch on the generating unit to energize the system.

(2) Check that the elevation clutch lever is in the "IN" position (oil gear engaged).

(3) Turn on the elevation limit switch on the gun carriage to energize the elevation oil gear. (The elevation oil gear clutch should always be engaged before the elevation switch is turned on.)

(4) When the director picks up the target, bring the gun into line with the director by traversing the gun until the azimuth indicator pointers match (or blacks out). It is not necessary for the azimuth indicator to match exactly (or black out exactly) when bringing the gun into line, as the gun will fall into line with the director if it is initially alined within 10 degrees.

(5) Now depress the power synchronizing ("SLEWING") handle. This operation throws the azimuth switch and engages the clutch in the azimuth oil gear.

(6) After the director picks up and tracks the target, it computes the firing azimuth and quadrant elevation and transmits these electrically to the oil gears which operate the gun. All human pointing errors at the gun are eliminated by the remote control system. Once the target is picked up and a rate set in, no correction can be made at the gun.

(7) Whenever the gun has engaged one of the elevation limit stops and tripped the elevation limit switch, it will be necessary to elevate or depress the gun manually by engaging the hand crank until it is brought inside the cut-off limit, and realined with the director.



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As soon as this has been done, disengage the hand crank and reset the elevation limit switch.

e. Changing Targets.

(1) When the order is given to track a new target, lift the power synchronizing handle and slew the gun to aline with the director again. When the azimuth indicator matches (or "blacks out"), indicating alinement with the director, depress the lever to engage the clutch.

(2) The elevation clutch and switch should remain engaged throughout active operation, as there is no provision for slewing the gun in elevation.

f. Cease Tracking. Both gun and the director should be set at an elevation of 30 degrees (or any other selected elevation, provided the same setting is used at both the gun and director) so that a new target can be picked up without delay.

g. Operating Faults.

(1) If the gun does not follow the director both in azimuth and elevation when tracking a target, the errors made are caused either by the mistakes of the operators at the director and the gun or by some mechanical or electrical imperfections in the remote control system or the director. Operating faults at the gun may be the following:

(a) Bad Lining-up. The breech peep sight and muzzle cross bars should be used, if they are available (par. 95).

(b) Gun Out of Level. The correct leveling of the gun cannot be overstressed. Any error in leveling will cause a corresponding error in elevation.

(c) Depressing the power synchronizing handle before the gun is approximately in line with the director (within 10 degrees).

(d) Turning on limit switch before gun is approximately in line with the director (within 10 degrees).

(e) Forgetting to reset the elevation limit switch after it has been automatically thrown to "OFF."

(2) If the director is operated at maximum rate and with maximum range it is possible for gun to "jump phase" in elevation, that is, synchronize within the next 20-degree sector.

(3) In cold weather, if oil gears are not properly warmed up before tracking with director, a similar condition as noted above can also occur.

h. Precautions. The following precautions should be taken in the operation and maintenance of the system:

(1) Power should be switched off before cables are connected or disconnected. See that cables are securely held in the receptacles before turning the power on.



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Figure 182 - Indicators on Clutch Housing and Output Coupling for accuracy test
Figure 182 - Indicators on Clutch Housing and Output Coupling for "Accuracy Test"

(2) The elevation clutch lever should be put in the "IN" position (top of lever away from the coupling) before switching on the power supply.

(3) Never put oil from an unsealed container in the oil gears.

(4) Be sure that the oil gears have been filled with oil correctly as noted in paragraph 102.

(5) Be sure the carriage is level before firing. The correct leveling of the carriage cannot be overstressed.

(6) In orienting for elevation or in adjusting oil gears to neutral, the unit cover plates should not be removed when dust or rain can get into unit, unless unavoidable. If it is necessary to remove covers under adverse conditions, the units should be protected to insure that no dust or rain gets into the unit.

i. Practice Tracking. To avoid damage to the electrical units when practicing with the director, energize the oil gears at the gun, and practice with the gun under direct control, or disengage the clutch on the elevation oil gear and turn on power on that gear, and throw in the power synchronizing handle at the gun (in order to protect the azimuth oil gear and the azimuth indicator unit).

98. TESTS AND ADJUSTMENTS OF REMOTE CONTROL SYSTEM M5.

a. General. The following described tests and adjustments must be made at regular intervals in order to insure proper operation of the system. All of these tests and corrective adjustments are made "on-carriage."



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b. Accuracy Test and Adjustment.

(1) The purpose of this test is to check over-all operation of system. Place a reference mark or indicator on the clutch housing and a corresponding mark made on circumference of output coupling (fig. 182). Traverse the director exactly 6 degrees (14 degrees for checking elevation unit), making sure that director does not overrun reading. The output coupling should make one complete revolution ± 1/16 inch (3 revolutions ± 3/32 inch for elevation). Test should be run in both directions.

(2) If unit does not meet accuracy test requirement, the following operations are required:

(a) Adjust dither (subpar. d, below).

(b) Make neutral ("creep") adjustment (subpar. e, below).

(c) Add oil to make up any deficiency (par. 102).

(d) Make backlash test and adjustment of transmitter gearing (subpar. c, below).

c. Adjustment of Backlash in Transmitter Gearing.

(1) Remove cover plate over transmitter units.

(2) Check for backlash or play between the teeth of the spiral gear and the pinion.

(3) If adjustment is necessary, loosen the screws holding the pinion shaft bearing bracket (fig. 183).

(4) Press the bracket upward, adjusting so that the pressure is as light as possible while there is no play between the gears.

(5) Reclamp the screws and test again to be sure that the gears run together smoothly and freely after adjustment.

CAUTION: This adjustment should be made only by qualified battery mechanic.

d. Dither Adjustment.

(1) The dither mechanism is such that it sets up a vibration in the oil gear which can be felt by placing the hand on the output coupling of the oil gear and twisting slightly to take up the slack. Adjustment of the dither is made as follows:

(a) To the left side of the oil gear on the case appears the word "DITHER" (A, fig. 184).

(b) Remove the hexagonal cap.

(c) With a screwdriver, turn the adjusting screw (B, fig. 184) until a definitely perceptible tremble is felt on the output coupling of the oil gear. Turn to the left to increase, to the right to decrease the vibration.

(2) Proper adjustment of the dither is best made by a sense of feel, but generally the correct adjustment is such that it will not cause the gun tube to tremble but will give a vibration to the output coupling of the oil gear which is just barely visible. Insufficient dither results in an inaccurate and insensitive gun, and excessive dither



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Figure 183 - Transmissitter Spiral Gear and Pinion and Pilot Valve
Figure 183 - Transmitter Spiral Gear and Pinion and Pilot Valve


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Figure 184 - Dither Adjustment
Figure 184 - Dither Adjustment

may cause low top speed, rough tracking, or slightly erratic action. It is necessary to have the oil gear thoroughly warmed up before making the adjustment, as the dither is noticeably affected by temperature.

(3) After making the dither adjustment, always make the neutral ("creep") test (subpar. e, below), as adjustment of the dither may cause oil gear to creep again by disturbing the pilot valve adjustment.

CAUTION: Do not turn dither adjusting screw more than several turns, as otherwise the mechanism may become disengaged.

e. Neutral ("Creep") Adjustment.

(1) When the director is not tracking, the pilot valve should be in neutral position so that there is no turning (or "creep") of the oil gear output coupling.

(2) With the oil gear clutch engaged, switch power off at the generating unit, and remove director cable from gun junction box. It is imperative that the director be disconnected from the gun while testing for, and while making neutral (creep) adjustment. This will make the electrical differential "electrically dead" and allow springs to hold torque arm (fig. 183) in neutral position. Turn power on.

(3) Observe the output coupling of oil gear unit and notice if there is any rotation (creep). If there is any creep, time it. Maximum allowance for creep is one revolution in 2 minutes. If creep is more than this rate, neutral (creep) adjustment should be made.

(4) Make adjustment by turning the adjusting thumbscrew (A, insert, fig. 185) until the creep of the output coupling is removed.

(5) Move the differential torque arm up and down slightly and



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Figure 185 - Making the Neutral (creep) adjustment
Figure 185 - Making the Neutral ("Creep") Adjustment

then allow it to spring back into neutral position. Repeat several times in alternate direction, observing whether the output coupling comes to rest without creep after each release, repeating the neutral (creep) adjustment if necessary, until creep has been satisfactorily removed.

(6) It is possible that the pilot valve may become stuck and operation described in step (5), above, will not free it. In that case, remove the pilot valve (as instructed in par. 100 a), clean with SOLVENT, dry-cleaning, and replace (as instructed in par. 100 b).

f. Adjustment of Resetter Spiral Gear.

(1) If, after making orienting operations described in paragraph 97 c, the gun and director are not oriented in elevation, an adjustment is made to position the rotor of the gun transmitter.

(2) Remove cover plate on right side of elevation oil gear unit.

(3) With power turned on, insert adjusting key in hole in large spiral gear so that teeth on key. mesh with teeth on smaller gear (fig. 186).

(4) Loosen the three set screws in small gear and turn key.

(5) Turning key rotates transmitter rotor, energizes oil gear unit, and moves gun.

(6) When gun is in proper orientation in elevation, the gun transmitter and director transmitter are alined.

(7) Tighten three set screws firmly and remove key.

(8) If no adjusting key is available, the adjustment may still be



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Figure 186 - Adjustment of Resetter Spiral Gear
Figure 186 - Adjustment of Resetter Spiral Gear



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Figure 187 - Adjusting Elevation Limit Stops
Figure 187 - Adjusting Elevation Limit Stops


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Figure 188 - Adjusting Azimuth Switch
Figure 188 - Adjusting Azimuth Switch

made by loosening the three set screws and turning the small steel gear by hand to bring the gun into alinement. However, an accurate adjustment by hand is difficult and the key should be used if it is available.

g. Torque Test. This test is to check power developed by oil gear. A low rate is set in director. The gun should follow smoothly without lag. If this condition is not met, check oil level and voltage and frequency at power plant. If oil level and power are satisfactory, increase dither slightly. If unit still cannot meet the test, replacement of the oil gear unit by qualified battery specialist should be made (as per instructions contained in par. 101 b and c). The defective unit should be turned over to ordnance maintenance personnel.

h. Adjustment of Elevation Limit Stops.

(1) The elevation limit switch must be set so as to cut the power off the elevation oil gear before the gun hits the mechanical stops or some other obstruction such as the parapet. Normally the upper cut-off point should be 85 degrees ±1 degree and the lower one may be anywhere between -5 and +8 degrees depending on local emplacement.

(2) To check the setting of the stops, elevate or depress the gun until the motor cuts off and then note the reading on the elevation indicator of the gun.

(3) To adjust the lower limit, loosen the two upper stud bolts.



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These are usually accessible through a slot of the cut-out switch plate (A, fig. 187). If not, the plate must be removed and the bolts loosened (B, fig. 187).

(4) To adjust the stops, change the position of the blocks on the rotating plate until the desired limit is obtained.

(5) If necessary to adjust upper limits, remove plate, loosen lower bolts, and change position of lower blocks.

i. Adjusting Azimuth Switch. The switch should snap on just after the oil gear clutch is engaged by throwing the power synchronizing ("SLEWING") handle. Adjustment is made by changing the spring tension on the azimuth oil gear clutch lever (fig. 188).

99. MALFUNCTIONS AND CORRECTIONS, REMOTE CONTROL SYSTEM M5.

a. General. The operations described in paragraphs 99, 100, and 101 can be performed by the using troops under supervision of competent personnel. Any further maintenance operations, such as disassembly of oil gears or azimuth indicator, should be done only by ordnance maintenance personnel. Periodic examination of the various units should be made to insure that the system will not become inoperative due to the need of some minor adjustment or repair that could have been readily performed prior to the time of operation.

b. If the Induction Motor in Either Oil Gear Does Not Run When Power Is Applied. The trouble may be due to blown fuses in the elevation limit switch or azimuth switch. There are three fuses in each switch box. The fuses are accessible for replacement on removal of the switch box cover. Fuses are rated 15 amperes, 250 volts. Remove power from the system before attempting to replace fuses. Secure switch box cover tightly after fuse replacement.

c. If No Power Is Available at Oil Gear or Director. The trouble may be in main switch of generator. The switch should be operated slowly but firmly since, if it is flipped on, it may cause the contacts to bounce.

d. Wiring Connections. When checking wiring connections after repair and replacement or when searching for bad or wrong wiring connections, use the wiring diagram, described in paragraph 101 b (6) (fig. 195).

e. Single Phase Operation of Oil Gears.

(1) Each oil gear is driven by a 3-phase induction motor supplied with electric current through three wires from the generator. If, for any reason, one of these wires is broken so that the electric current is carried through only the other two wires, the motor will receive what is technically known as "single phase current." Under such a condition, the motor will not start. Instead, the motor merely emits



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a moderately loud hum without even giving a jerk or any other indication of starting. The motor will draw a heavy current of about 18 or 20 amperes from the generator which may be observed on the generator ammeter (except that if line "C" is the open one, the ammeter will read "0"). The heavy current drawn will cause the generator to slow down and probably start to "hunt." The voltage indicated on the generating unit voltmeter will have dropped to about 60 to 70 volts and the maximum adjustment of the rheostat generally will not bring the voltage back to 125 volts.

(2) Single phase operation of the motors is easily detected when the symptoms are known. When this condition does occur, the gun switch should be turned off immediately because the current drawn, if left on for more than a few seconds, is large enough to burn out the gun fuses or possibly damage the motor and generator.

(3) The most common cause for single phase operation of the motor is the failure of the gun switch to close properly. This may be overcome as follows:

(a) Snap the switch on quite hard.

(b) Open the switch box and bend the contact fingers slightly so that a smooth, easy contact is made.

(c) Remove burs. Burs may be removed from the fingers with sandpaper, or CLOTH, abrasive, aluminum-oxide.

NOTE: Oil or grease should not be placed on the fingers, as it interferes with good electrical contact.

(4) Another cause of single phase operation of a motor is a burned out fuse on either the gun or generator.

(5) In addition, if the generator cable plug at either gun or generator end is improperly connected so that one of the small prongs goes in the large hole, an open circuit may arise and result in single phase operation. The large prong marked "A" should go in the large hole marked "A" (fig. 170).

f. Oil Gear Motors Running Backwards.

(1) Reversed oil gear motors can easily be detected by the characteristic dry sound of the oil gear; by the fact that the gun gives absolutely no indication of moving; and by removing the top plug of the chain case and noting whether or not the chain is running in the direction of the arrow on the motor housing.

(2) If an oil gear motor is found to be running backwards, first check the other oil gear motor and the director motors.

(3) If all motors are running backwards, this should be corrected at the generator by interchanging any two of the three conductors attached to one end of the fuses.

(4) If only one oil gear motor is running backwards, reverse it by interchanging any two of the three leads connected to the terminals at the top of the motor (fig. 192).

g. Reversed Tracking of the Gun. If the gun tracks smoothly



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and accurately but in a direction opposite to that of the director, two of the wires to the electrical differential are interchanged. A quick correction can be made by interchanging any two of the three "S" leads or any two of the three "R" leads to the differential; however, as soon as time permits, the wiring should be checked for the original mistake and connected according to the wiring diagram (fig. 195).

h. Basic Trouble Shooting. The procedure for the using personnel in case of malfunctioning of any part of the remote control system is to attempt to locate the major unit in which the fault originates. Faults which appear as malfunctions of the remote control system may be in the director or in another unit of the system. To isolate the trouble to one of the three basic parts of the system, i.e., the mechanical part of the director, the electrical signaling system, or the hydraulic part of the oil gear, proceed as follows:

(1) WATCH THE DIALS ON THE DIRECTOR. The gun should follow the dials exactly. If the dials behave in the normal fashion, and the gun is erratic, the trouble is in either the hydraulic part of the oil gear or the electrical signaling system. If the dials are erratic, the trouble is in the mechanical part of the director.

(2) OPERATE THE OIL GEAR PILOT VALVE MANUALLY. If the gun responds normally, the trouble is in the electrical signaling system. If it does not, the trouble is in the hydraulic part of the oil gear.

(3) AS A ROUGH CHECK, MOVE GUN OR DIRECTOR MANUALLY AND WATCH THE DEFLECTIONS OF THE ELECTRICAL DIFFERENTIAL TORQUE ARM. If the torque arm deflects normally, the trouble is in the hydraulic part of the oil gear. If it does not, the trouble is in the electrical signaling system.

(4) Troubles in the mechanical part of the director are covered in the director manuals.

(5) Troubles in the electrical signaling system are difficult to isolate and should be referred to ordnance maintenance personnel.

(6) Troubles in the hydraulic part of the oil gear fall into three classifications as follows:

(a) The Gun Runs Continuously in One Direction.

1. Operate the pilot valve manually (fig. 183).

2. If this fails to affect the action, remove the pilot valve (par. 100 a).

3. Disengage azimuth oil gear clutch by blocking (fig. 176).

4. Run oil gear for 10 minutes.

5. Replace pilot valve (par. 100 b) and check operation.

6. If the trouble has not been corrected, replace the oil gear with a spare, and request ordnance maintenance personnel to repair the faulty one.

(b) The Gun Develops Low Top Speed.

1. This malfunction is evidenced by a tendency to "skip phase";



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that is, the gun jumps from one "phase" or synchronous point to another when director is tracking too rapidly. As shown on the azimuth indicator, the pointers are outside the limit lines, and therefore the gun will not synchronize with the director.

2. Run the oil gear to allow it to warm up thoroughly.

3. Measure the top speed of the gun by riding the carriage and manually holding the sensitive valve full open.

4. The gun should make one revolution in azimuth in not more than 18 seconds in either direction, and in elevation, it should make 65 degrees in not more than 4 seconds in either direction.

5. If the speed of the gun is low, add hydraulic oil to make up any deficiency.

6. Adjust the dither (par. 98 d).

7. Adjust the neutral creep (par. 98 e).

8. Again measure the top speed and, if it is still low, replace the oil gear with a spare and call ordnance maintenance personnel to repair the faulty one.

(c) In Tracking, the Gun Is Rough or Jerky.

1. Add hydraulic oil to make up any deficiency.

2. Adjust the dither (par. 98 d).

3. Adjust the neutral creep (par. 98 e).

4. If the gun is still rough, replace the oil gear with a spare and call ordnance maintenance personnel to repair the faulty one.

100. REMOVAL AND REPLACEMENT OF PILOT VALVE.

a. Removal of Pilot Valve.

(1) Remove the hex-head plug and copper asbestos gasket located at the front right corner on the top of the top case (fig. 183).

(2) Remove the six nuts from studs holding the right side plate to the top case.

(3) Remove the plate.

(4) Loosen with a screwdriver, the four screws of the differential bakelite retaining ring, located inside the left side of the top case assembly (A, fig. 189).

(5) Free the pilot valve adjusting thumbscrew from the arm of the differential (right side of the top case) (B, fig. 189). This is accomplished by pressing against the spring lip on the synchro differential torque arm, and by carefully moving the thumbscrew to the right until it is free of the differential torque arm.

(6) Slide the differential back (about 1/2 inch) by pressing against the differential arm from the right side of the top case (B, fig. 189).

(7) Grasp the thumbscrew and carefully remove the pilot valve assembly from the oil gear by lifting out through the hex-head plug hole (C, fig. 189).

(8) Replace the hex-head plug and copper-asbestos gasket in the plug hole.



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Figure 189 - Removing the Pilot Valve
Figure 189 - Removing the Pilot Valve


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Figure 190 - Replacing Pilot Valve
Figure 190 - Replacing Pilot Valve

CAUTION: Exercise care in handling the pilot valve. Do not touch the valve proper with the hands, as dirt and perspiration are detrimental to it. While the valve assembly is out of the oil gear wrap it in a piece of clean paper and keep it in a safe place so as to prevent burring or scratching.

b. Replacement of Pilot Valve.

(1) There is provided in each set of oil gear tools a tube for quickly and accurately inserting the pilot valve into the plunger of the relay valve of the oil gear. It should always be used in inserting this valve, as otherwise the valve may become caught in the mechanism and require disassembly of the oil gear to free it.

(2) Precaution. Be sure tool is absolutely clean before using. Clean with SOLVENT, dry-cleaning.

(3) Be sure that the differential has been pushed back as described in subparagraph a (5), above, before using the tool.

(4) Insert the tool bell-mouth down, through the 1/2-inch hole in the top of the transmitter and differential housing and through the sensitive valve tube until it seats over the plunger in the relay valve (A, fig. 190).

(5) Now install the sensitive valve by slipping it down into the tube (B, fig. 190).

(6) Withdraw the tube.

(7) Slide differential forward, position properly with the pin



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Figure 191 - Removing Top Cover From Oil Gear Motor Terminal Block
Figure 191 - Removing Top Cover From Oil Gear Motor Terminal Block

against the bracket stop, and tighten the four screws in the bakelite retaining ring, on the opposite side (A, fig. 189).

(8) Press the valve stem back into the spring clip of the differential torque arm.

(9) Adjust the dither (par. 98 d).

(10) Make neutral ("creep") adjustment (par. 98 e).

(11) Replace cover plates.

101. REMOVAL, REPLACEMENT, AND CONVERSION OF OIL GEAR UNITS.

a. The using troops are permitted to perform unit replacements of oil gears in case of failure of a unit, but proper facilities must be available to prevent entrance of dust into the interior when cover plates are removed.

b. Removal of Oil Gear Units.

(1) Remove the terminal cover plate on top of the motor (fig. 191).

(2) Note the lead markings (mark the leads if there are no lead markings) to insure that the leads can be reconnected to the corresponding terminals.

(3) Loosen the three terminal screws (fig. 192) and disconnect the wires.

(4) Remove the four screws securing the cable adapter to the motor housing and withdraw the conduit from the terminal well (fig. 193).

(5) Remove the terminal side cover (fig. 194) over the transmitter and electrical differential assembly, exposing the terminal screws. This cover is on the same side as the clutch lever.



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Figure 192 - Disconnecting Wires From Terminal Block
Figure 192 - Disconnecting Wires From Terminal Block

Figure 193 - Removing Conduit From Terminal Well
Figure 193 - Removing Conduit From Terminal Well



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Figure 194 - Removing Oil Gear Side Cover Plate
Figure 194 - Removing Oil Gear Side Cover Plate

Figure 195 - Wiring Diagram for Oil Gears
Figure 195 - Wiring Diagram for Oil Gears

(6) Now refer to figure 195, the wiring diagram for oil gears. Disconnect three leads (RI, R2, and R3) to the differential and two leads (X and Y) to the resetter transmitter by loosening the terminal screws. Do not disconnect the interconnecting leads (Si, S2, S3, and 1, 2, 3). Note the lead markings (mark the leads if there are no lead markings) to insure that the leads can be reconnected to their corresponding terminals.

(7) Remove the three screws securing the cable adapter to the housing (fig. 196) and withdraw the wires from the housing.

(8) Remove the four bolts securing oil gear to carriage (A, fig. 197) and the single bolt at rear of induction motor (B, fig. 197).

(9) Remove the oil gear by pulling it forward from the front of



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Figure 196 - Disconnecting Wires From Oil Gear Synchro Transmitters
Figure 196 - Disconnecting Wires From Oil Gear Synchro Transmitters

Figure 197 - Disconnecting Oil Gear From Carriage
Figure 197 - Disconnecting Oil Gear From Carriage

the carriage, being careful not to damage the drive shaft or coupling mechanism (fig. 198).

(10) When removing an azimuth oil gear, disconnect the rod from the lower end of the clutch shaft lever.

(11) If the coupling is frozen to the spline shaft of the gun drive mechanism, then remove rubber seal from oil gear coupling by using small screwdriver (fig. 199).



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Figure 198 - Removing Oil Gear Assembly
Figure 198 - Removing Oil Gear Assembly

Figure 199 - Removing Rubber Seal From Oil Gear Coupling
Figure 199 - Removing Rubber Seal From Oil Gear Coupling

(12) Note that in replacing a unit, a distinction must be made between the azimuth oil gear and the elevation oil gear. Although both units are similar in outward appearance, they cannot be interchanged, as their gearing ratios are different. The azimuth unit has



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a coarse (64-tooth) spiral gear on the resetter transmitter, while the elevation unit has a fine (108-tooth) spiral gear (fig. 183). In the absence of accurate name plate data, the unit can be positively identified by removing the right side (adjusting side) cover and note either the piece marks or whether the coarse or fine toothed pinion is meshed with bronze spiral gear of the gun transmitter, according to the following data : The fine is the elevation, the coarse is the azimuth one. If piece marks are visible this is the best means of identification; otherwise, count the teeth in the spiral gear.

Type of Unit Piece Marks Spiral Gear
Elevation A182177 108 teeth
Azimuth A182178 64 teeth

CAUTION: Oil gears must be kept level at all times in order to prevent oil from entering the electrical units above the oil gear motors.

NOTE: Oil gears may be shimmed at the bases. Care should be taken that these shims are not lost. The oil gear side plate covers and terminal block covers should be replaced to prevent dirt from entering the oil gear assembly.

c. Replacement of Oil Gear Units.

(1) Place oil gear on carriage.

(2) Insert wires into housing through proper openings.

(3) Connect leads R1, R2, and R3 to the differential and leads X and Y to the gun transmitter. Leads should have been tagged when the unit was disassembled.

(4) Connect motor leads to proper terminals in terminal well.

NOTE: The black leads from the terminal strip into the motor are for 60-cycle operation.

(5) Slide gear into position to engage the drive shaft. Be careful not to damage the drive shaft or coupling mechanism. Be sure to replace the rubber seal if it has been removed from the oil gear coupling, pulling seal over coupling towards the oil gear.

(6) Insert the five bolts that fasten the oil gear to the carriage. Start the nuts but do not tighten them. (Refer to fig. 197)

(7) The oil gear must be fastened on the carriage so that the coupling faces are parallel. For lateral alinement, shift the oil gear sidewise within the play around the bolts until the "GO" part of the coupling gage fits equally over both sides of the coupling (A, fig. 200) and the "NO GO" part does not (B, fig. 200). For vertical alinement, try the coupling gage on the top and bottom of the coupling. If the "GO" part of the gage does not fit equally over both top and bottom of the coupling, the oil gear may be shimmed with shim stock, or in emergency with paper, until the coupling faces are parellel. In general, however, it is not necessary to do this as the oil gear mounting plate is properly set at the proving grounds. When the oil gear is alined, tighten the bolts and, on an azimuth unit, connect the rod



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Figure 200 - Checking Coupling Faces for Parallelism With go and no gage
Figure 200 - Checking Coupling Faces for Parallelism With "GO" and "NO GO" Gage

from the power synchronizing ("SLEWING") handle to the lower end of the clutch shift lever.

(8) Try the oil gear. If the motor is reversed or the gun runs backwards, proceed as in paragraph 99.

(9) After replacing an oil gear, it is necessary to reorient the gun (par. 97 c).

d. Conversion of Elevation Oil Gear to Azimuth Oil Gear or Vice Versa.

(1) One spare azimuth oil gear (assembled) and one spare elevation oil gear (assembled) are furnished with each eight guns.

(2) In order to convert an elevation oil gear to an azimuth unit or vice versa, the right-hand side cover plate must be removed. To identify the respective units (if nameplate data is lacking) and to be sure that the right parts are reassembled, use the data noted in subparagraph I) (12), above. If piece marks are visible, this is the best means of identification; otherwise, count the gear teeth.

(3) The three screws clamping the spiral gear between the disk and adapter on the gear assembly (step 1, fig. 201) must be withdrawn, the adapter removed (step 2), and the spiral gear removed (step 3).



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Figure 201 - Conversion of Oil Gear From Azimuth to Elevation or Vice Versa
Figure 201 - Conversion of Oil Gear From Azimuth to Elevation or Vice Versa



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(4) The taper pin securing the double pinion (fine pinion for elevation, coarse pinion for azimuth) must be driven out. Note the following precautions and instructions:

(a) Be sure to drive the taper pin through from the small end. Rotate the pinion and note carefully the relative size of the pin ends, until certain which is the smaller end.

(b) Insert a screwdriver or other firm tool under the pinion shaft (step 4, fig. 201) in order to support the shaft while driving out the pin. This will prevent bending or breaking the aluminum bearing bracket.

(c) Drive out the pin using a drift tool or a drive pin punch (step 5, fig. 201).

(5) Slide pinion over to the other side of the shaft (engaging the fine pinion if it is desired to convert to elevation, and coarse pinion if it is desired to convert to azimuth) (step 6, fig. 201).

(6) Secure in place by inserting taper pin into the hole provided (step 7, fig. 201)

(7) Mount the appropriate spiral gear (mount the fine spiral gear if converting to elevation, or the coarse spiral gear if converting to azimuth).

(8) Replace the disk.

(9) Secure the gear and disk to the adapter by means of the three screws that were withdrawn, taking care to mesh the gear with the correct pinion, as instructed in step (5), above.

(10) Check backlash between the pinion and gear. Adjust so that the pressure between teeth of the pinion and gear is as light as possible while there is no play between the gears. The adjustment is made by loosening the screws holding the bearing bracket, pressing the bracket upward and reclamping the screws. (To be done only by battery electrician.)

(11) Where only one lug is provided on the bell housing, it will be necessary on those units to remove the four nuts and studs holding the rear bell housing. In order to remove the studs with the nuts, mutilate threads on ends of studs so that nuts will not screw completely off. The studs will come out upon exerting pressure on nuts. After removing nuts with studs, rotate bell housing 180 degrees and secure in place.

(12) Precaution. Do not under any circumstances pull bell housing off motor. If this is done the rear motor bearings will fall out and replacement of the bearings necessitates use of a special tool which is not issued to the using arms. The bell housing is rotated to enable fastening the upper portion of the oil gear unit to carriage (bell housings which are equipped with two brackets need not be rotated).



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(13) Interchange the pipe plug and grease fitting in the clutch housing cover and secure in place.

(14) Remove the cotter pin on the shaft pin which supports the auxiliary locking lever (fig. 174), drive out the shaft pin, and remove the locking lever. Insert the spare sleeve, drive the shaft pin back in place, and secure it by means of the cotter pin.

(15) An azimuth unit can be converted to an elevation unit by reversing the above replacements and assemblies.

(16) When spare elevation oil gear is changed over into an azimuth oil gear and replaces the azimuth unit on the gun, be sure to switch nameplates. After having done this, change azimuth unit, which has just been removed from the gun, into an elevation oil gear. Nameplates will then be correct.

e. Tools and Equipment. A tool box containing tools and equipment for maintenance of the oil gear is furnished with the system. No screwdriver is provided as there is usually a screwdriver in the gun carriage tool box. The following tools are supplied. When not in use, these tools should always be kept in the tool box provided.
Coupling gage (for assembling oil gear to carriage)
Oil gun (for adding oil to unit)
Adjusting key (for adjusting resetter transmitter)
Spanner (for changing filter bobbin assembly)
Filling tube (for inserting sensitive valve)
12-point box wrench (3/8 and 7/16)
12-point box wrench (5/8 and 3/4)

102. LUBRICATION OF REMOTE CONTROL SYSTEM M5.

a. Lubrication and Replenishing of Oil.

(1) Cleanliness is of the utmost importance in handling the oil for the oil gears. When replenishing the oil supply of the oil gears, the oil must be taken from a container whose seal is unbroken. Dust or moisture must not be allowed to get into the oil while refilling, and the remaining oil in the container should be used for some other purpose or thrown away. The oil gun must be kept clean, and should be used only for the prescribed oil (step (3), below).

(2) It is a good practice to have one man replenish the oil in all oil gears in the battery at least once a week by carrying the can of oil from gun to gun and thereby minimize the waste of oil to a part of a can per battery, instead of a part of a can per gun.

(3) Since all oil gears leak oil around the pump and motor shafts, it is necessary to replenish the oil in the main case by pumping OIL, hydraulic, U. S. Army Specification 2-79A, through the filter until oil flows from the overflow hole in the side of the filling tube. This should be done once a week (subpar. 1) below). As ^ome oil gears become air locked, it may be necessary to loosen the pilot valve filling plug to let the air escape from the case while the oil is pumped in.



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Figure 202 - Pumping Oil Through the Filter of Oil Gear
Figure 202 - Pumping Oil Through the Filter of Oil Gear

(4) The oil gear, when filled with oil, must always be kept upright; otherwise, oil will get into the electrical control elements and cause damage. If, through accident, the oil does get into the electrical control compartment, remove the side covers from this compartment and wipe off the oil.

(5) Precaution. Unless the proper procedure is followed, the mechanic filling the oil gear may erroneously decide that the gear is filled, whereas the oil which appears at the location of the tell-tale hole in the oil filter assembly may actually have been spilled in the filling operation. If the oil gun is not centered in the bushing in the oil filter, spilling will occur. The oil gun can be centered in this bushing by first elevating the 40-mm gun barrel to its maximum position. When filling the elevation oil gear (B, fig. 202), hold oil gun firmly in line with the filter tube.



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b. Changing Oil.

(1) Remove pilot valve (par. 100 a).

(2) Leave elevation oil gear disengaged when changing oil in elevation oil gear.

(3) Block azimuth oil gear clutch (fig. 178) in disengaged position when changing oil in azimuth oil gear.

(4) Turn on oil gear and allow it to run for 10 minutes.

(5) Stop oil gear.

(6) Immediately remove drain plug under filling tube.

(7) Allow oil to drain from main case.

(8) Replace drain plug.

(9) Tighten securely.

(10) Replace pilot valve (par. 100 b).

(11) Refill by pumping OIL, hydraulic, through filter (fig. 202).

(12) Stop when oil flows from overflow hole in the side of the filling tube.

(13) Do not flush oil gear with solvent or gasoline as this would dilute the oil.

(14) Make neutral (creep) adjustment (par. 98 e).

(15) Reorient the gun (par. 97 c).

c. Renewing Filter Bobbin Assembly. The filter (filling tube) contains a filter bobbin assembly which may require replacement after several oil changes. The filter bobbin assembly consists of a bobbin shaped metal tube with a muslin strip wrapped around a perforated portion to form the filter element. To replace the filter bobbin assembly, proceed as follows:

(1) Remove cover (fig. 202).

(2) Using the spanner tool provided (A, fig. 203), unscrew the retainer at the top of the filter opening filling tube (B, fig. 203).

(3) Lift out the old filter bobbin assembly by grasping the top with the fingers and pulling out (C, fig. 203).

(4) Wash in SOLVENT, dry-cleaning. If the filter is damaged and ineffective or too dirty to be cleaned satisfactorily, replace it with a new one.

(5) Screw the retainer back into place.

CAUTION: Care must be taken during the foregoing operations to prevent entrance of dirt into the interior parts.

d. Chain Case and Clutch Housing.

(1) Drain oil from chain case daily, by removing level plug in chain case.

(2) Drain oil from clutch housing weekly, by removing level plug in clutch housing.

(3) Do not remove chain case cover. (Chains are not to be greased.)

(4) In replacing plugs, use care not to tighten sufficiently to strip threads in the aluminum chain case.



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Figure 203 - Renewing Filter Bobbin Assembly
Figure 203 - Renewing Filter Bobbin Assembly



251
 

Figure 204 - Lubrication of Transmitter Spiral Gear
Figure 204 - Lubrication of Transmitter Spiral Gear

e. Lubrication of Transmitter Spiral Gear.

(1) The resetter transmitter spiral gear (fig. 204) is lubricated by a cork lubricating ball located in a recess under the driving pinion.

(2) Fill this recess with hydraulic oil as prescribed in lubrication section.

(3) The cover over the spiral gear must be removed to permit lubrication (fig. 204).

(4) When lubricating spiral gear, note condition of cork ball. The ball must be replaced if it becomes "chewed up" (to be done by ordnance maintenance personnel).

(5) Sufficient oil to float the cork ball up to the opening must be kept in the oil recess.

f. Azimuth Indicator.

(1) The azimuth indicator has an oil cup fitted with a felt pad, located in top of housing.

(2) Every 6 months, apply 6 to 8 drops of OIL, lubricating, for aircraft instruments and machine guns, to these oil cups. Oil very sparingly, as excess oil will damage the indicator.

g. Contact Ring. Keep the area around the contact ring clean from oil, water, and dirt. In order to perform the cleaning operation, a portion of the cartridge case chute has to be removed.



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Section XI
AMMUNITION

103. GENERAL.

a. Ammunition for the GUN, automatic, 40-mm, M1, is issued in the form of fuzed complete rounds of fixed ammunition. The term "fixed" signifies that the propelling charge is not adjustable and that the round is loaded into the gun as a unit. The cartridge case, which contains the propelling charge and primer, is crimped rigidly to the projectile. A complete round includes all of the ammunition components (cartridge case, primer, propelling charge, and projectile) required to fire the gun once. All high-explosive projectiles are provided with point-detonating fuzes. In firing, the cartridge case is extracted and ejected automatically.

104. NOMENCLATURE.

a. Standard nomenclature is used herein in all references to specific items of issue. Its use for all purposes of record is mandatory.

105. FIRING TABLES.

a. For available firing tables, see section XV.

106. CLASSIFICATION.

a. Dependent upon the type of projectile, ammunition for this gun is classified as high-explosive (HE), high-explosive-tracer (HE-T), armor-piercing-tracer (AP-T), target-practice-tracer (TP-T), or drill. The projectile of the high-explosive round is relatively thin-walled and contains a high-explosive filler for fragmentation and blast effect. The projectile of the armor-piercing round is a solid shot, for penetration of armor-plate or other highly resistant targets. The practice ammunition has a service propelling charge but the projectile is inert and fitted with a dummy or inert fuze. It is provided for training in marksmanship. All types manufactured for Army use have tracer elements in the projectile base to facilitate observation of the path of flight. The tracer assembly of the high-explosive shell is known as a shell-destroying tracer because, in addition to providing a visible trace for observation, it will detonate the bursting charge at the end of the trace burnout should the projectile fail to strike the target or fail to explode as a result of impact. The drill cartridge is a completely inert assembly.

107. IDENTIFICATION.

a. General. Ammunition is identified by painting and marking which appears on all original packing containers and, when practicable,



253
 
on the items themselves. Identifying markings on packing boxes are shown in figure 208, and are listed with other markings for shipment in paragraph 113. It will be noted that the marking includes the muzzle velocity. When removed from packing, the ammunition is identified as indicated in the paragraphs below when of Army procurement. In other cases, painting and marking may differ in form but essentially the same information will be given.

b. Mark or Model. To identify a particular design, a model designation is assigned at the time the model is classified as an adopted type. This model designation is included in the marking of the item. Components originated by the Army are designated by the letter "M" followed by an Arabic numeral, for example, "M64." Modifications are signified by adding the letter "A" and appropriate Arabic numeral. Thus, "M64A1" signifies the first modification of an item for which the original designation was "M64." Components originated by other services are designated in accordance with the practices of those services. (Navy practice is to use the word "Marks", abbreviated "Mk.," followed by either a Roman or an Arabic numeral.)

c. Ammunition Lot Number. In addition to the lot number assigned to every ammunition component and usually stamped thereon, assembled complete rounds are assigned an ammunition lot number at the time of assembly. This ammunition lot number is stenciled on all original packing containers and, when practicable, on the assembly itself. It is required for all purposes of record, including reports on condition, functioning, and accidents, in which the ammunition is involved. For the most uniform results in firing, successive rounds should be from the same ammunition lot.

d. Marking. The 40-mm rounds are marked for identification as follows:

(1) STENCILED ON THE PROJECTILE.

(a) Caliber and type of cannon in which fired.

(b) Type and model of projectile.

(c) Kind of filler (on HE projectiles).

(d) "WITH TRACER" (when applicable). This marking will include the model of tracer.

(e) Ammunition lot number and loader's initials. *

(f) Lot number of filled projectile. (Ordinarily the projectile lot number is not required after the complete round is assembled. Hence, it is stenciled below the rotating band, in which position it is covered by the neck of the cartridge case.)

(2) STAMPED ON THE ROTATING BAND.

(a) Lot number of empty projectile.


* Ammunition lot number formerly appeared on the base of the cartridge case.


254
 
(b) Year of manufacture.

(c) Initials or symbol of manufacturer.

(d) Caliber and model of shot or shell.

(3) ON THE BASE OF THE CARTRIDGE CASE.

(a) Caliber and model of cartridge case (stamped).

(b) Cartridge case lot number, manufacturer's initials and year manufactured (stamped).

(4) ON THE FUZE (STAMPED IN BODY).

(a) Model designation of fuze.

(b) Manufacturer's initials.

(c) Lot number of fuze.

(d) Year of manufacture.

e. Painting. Projectiles are painted primarily to prevent rust; the secondary purpose is to provide, by the color, a ready means of identification as to type. The color scheme for 40-mm ammunition is as follows:

High-explosive Olive-drab, marking in yellow.
Armor-piercing (w/o explosive) Black, marking in white.
Target-practice Blue, marking in white.
Drill (dummy) Black, except bronze parts; marking in white.

108. CARE, HANDLING, AND PRESERVATION.

a. General. Ammunition is packed to withstand conditions ordinarily encountered in the field. Care must be observed to keep packing containers from becoming broken or damaged. All broken containers must be repaired immediately and careful attention given to the transfer of all markings to the new parts of the container.

b. Since explosives are adversely affected by moisture and high temperature, due consideration should be given the following:

(1) Do not break the moisture-resistant seal until ammunition is to be used. Ammunition removed from airtight containers, particularly in damp climates, is apt to corrode, thereby causing the ammunition to become unserviceable.

(2) Protect the ammunition, particularly fuzes, from sources of high temperature, including the direct rays of the sun. More uniform firing is obtained if the rounds are at the same temperature.

c. Explosive ammunition must be handled with appropriate care at all times. The explosive elements in primers and fuzes are particularly sensitive to undue shock and high temperature.

d. Ammunition should be protected from mud, sand, dirt, and water. If the rounds become wet or dirty, they should be wiped off at once. Verdigris or light corrosion should be wiped off.



255
 
Ammunition should not be polished, however, to make it look better or brighter.

e. Rounds prepared for firing but not fired will be returned to their original condition and packing, and appropriately marked. Such ammunition will be used first in subsequent firing in order that stocks of opened packings may be kept at a minimum.

f. Do not handle duds. Because their fuzes are armed, and hence extremely dangerous, duds will not be moved or turned, but will be destroyed in place in accordance with TM 9-1900.

109. AUTHORIZED ROUNDS.

a. Ammunition authorized for use in GUN, automatic, 40-mm, M1, is listed in table I and illustrated in figures 205 to 207. It will be noted that the nomenclature (standard nomenclature) completely identifies the round. The numbers in parentheses preceding the nomenclature refer to assembly numbers in table II, which contains ammunition data.



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TABLE I - AUTHORIZED ROUNDS

  SERVICE AMMUNITION
(1) CARTRIDGE, AP-T, M81A1, 40-mm AA. guns
- CARTRIDGE, AP-T, M81A1, steel case, 40-mm AA. guns
(2) CARTRIDGE, AP-T, M81, 40-mm AA. guns
(3) CARTRIDGE, HE, Mk. I (Navy), w/FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns
(4) CARTRIDGE, HE-T (SD, M3), Mk. II, w, FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,700 f/s)
- CARTRIDGE, HE-T (SD, M3), Mk. II, steel case, w/FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,700 f/s)
(5) CARTRIDGE, HE-T (SD), Mk. II, w/FUZE, P.D., M71, 40-mm AA. guns (muzzle velocity 2,700 f, s)
(6) CARTRIDGE, HE-T (SD, M3), Mk. II, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,700 f/s)
- CARTRIDGE, HE-T (SD, M3), Mk. II, steel case, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,700 f, s)
(7) CARTRIDGE, HE-T (SD, No. 12), Mk. II, w/FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,700 f/s)
- CARTRIDGE, HE-T (SD, No. 12), Mk. II, steel case, w/FUZE, PD., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,700 f/s)
(8) CARTRIDGE, HE-T (SD, M3), Mk. II, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,870 f/s)
- CARTRIDGE, HE-T (SD, M3), Mk. II, steel case, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,870 f/s)
(9) CARTRIDGE, HE-T (SD, No. 12), Mk. II, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,870 f/s)
- CARTRIDGE, HE-T (SD, No. 12), Mk. II, steel case, w/FUZE, P.D., M64A1, 40-mm AA. guns (muzzle velocity 2,870 f/s)
(10) CARTRIDGE, HE-T (SD, No. 12), Mk. II, w FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,870 f/ s)
- CARTRIDGE, HE-T (SD, No. 12), Mk. II, steel case, w/FUZE, P.D., Mk. 27 (Navy), 40-mm AA. guns (muzzle velocity 2,870 f, s)
(11) CARTRIDGE, HE-T (SD), Mk. II, w/FUZE, P.D., 251, Mk. I, 40-mm AA. guns (muzzle velocity 2,870 f, s)
- CARTRIDGE, HE-T (SD), Mk. II, steel case, w/FUZE, P.D., 251, Mk. I, 40-mm AA. guns (muzzle velocity 2,870 f/s)
  PRACTICE AMMUNITION
(12) CARTRIDGE, TP-T, M91, w FUZE, dummy or inert, M *, 40-mm AA. guns (muzzle velocity 2,700 f, s)
(13) CARTRIDGE, HE-T, Mk. II, inert loaded, w/FUZE, dummy or inert, M *, 40-mm AA. guns (muzzle velocity 2,700 f, s)
  DRILL AMMUNITION
(14) CARTRIDGE, drill, M17, 40-mm AA. guns

*-FUZE, dummy, M69; or inert FUZE, P.D., M64, M64A1, Mk. 27, 251 Mk. I, or other suitable types may be assembled to the projectile.


257
 
Figure 205 - Cartridge, AP-T, M8A1, 40-mm AA Guns
Figure 205 - Cartridge, AP-T, M8A1, 40-mm AA Guns


258-259
 

TABLE II - DATA ON AMMUNITION FOR 40-MM AA. GUN M1

NOTE: Data given for the rounds listed below are based on standard components. Complete rounds may be found which have been assembled from similar components manufactured by other service, interchanged components will be identified by the marking thereon.

PROJECTILE FUZE *PROPELLING CHARGE #PRIMER
Kind Type Model Weight
as
Fired
(lb)
Charge COMPLETE
ROUND
Type
and
Model
Action Type
of
Powder
Weight
(lb)
Muzzle
Velocity
f/s
Model Type
Kind Weight
(lb)
Weight
(lb)
Length
(in.)
SERVICE AMMUNITION
1 CARTRIDGE AP-T M81A1 1.96 None - 4.58 17.62 None - FNH 0.65 2870 M38A1 55-gr. perc.
2 CARTRIDGE AP-T M81 1.96 None - 4.53 17.62 None - FNH 0.65 2870 M23A2 20-gr. perc.
3 CARTRIDGE HE *** Mk. I (Navy) 2.0 TNT 0.1 4.6 17.60 P.D., Mk. 27 (Navy) Superquick FNH 0.66   Mk. 22 64-gr. perc.
4 CARTRIDGE HE-T(SD,M3) Mk.II 2.06 Tetryl 0.05 4.82 17.62 P.D., Mk. 27 (Navy) Superquick FNH 0.72 2700 M38A1 55-gr. perc.
5 CARTRIDGE HE-T(SD) Mk.II 2.06 Tetryl 0.05 4.82 17.62 P.D., M71 Superquick FNH 0.72 2700 M38A1 55-gr. perc.
6 CARTRIDGE HE-T(SD,M3) Mk.II 1.93 TNT 0.14 4.53 17.62 P.D., M64A1 Superquick FNH 0.72 2700 M38A1 55-gr. perc.
7 CARTRIDGE HE-T(SD,M3) Mk.II 1.93 TNT 0.168 4.82 17.62 P.D., Mk. 27 (Navy) Superquick FNH 0.72 2700 M38A1 55-gr. perc.
8 CARTRIDGE HE-T(SD,M3) Mk.II 2.06 Tetryl 0.05 4.49 17.62 P.D., M64A1 Superquick FNH 0.68 2870 M38A1 55-gr. perc.
9 CARTRIDGE HE-T(SD,No. 12) Mk.II 1.96 TNT 0.14 4.49 17.62 P.D., M64A1 Superquick FNH 0.68 2870 M38A1 55-gr. perc.
10 CARTRIDGE HE-T(SD,No. 12) Mk.II 1.93 TNT 0.168 4.78 17.62 P.D., Mk. 27 (Navy) Superquick FNH 0.68 2870 M38A1 55-gr. perc.
11 CARTRIDGE HE-T(SD) Mk.II 1.93 TNT 0.15 4.60 17.61 P.D., 251, Mk. I Superquick FNH 0.68 2870 M38A1 55-gr. perc.
PRACTICE AMMUNITION
12 CARTRIDGE TP-T% M91 1.99 None - 4.68 17.62 Dummy or inert, M** - FNH 0.72 2700 M38A1 55-gr. perc.
13 CARTRIDGE HE-T% Mk.II 1.99 Inert.
Loaded
- 4.68 17.60 Dummy or inert, M** - FNH 0.72 2700 M38A1 55-gr. perc.
DRILL AMMUNITION
14 CARTRIDGE Drill M17 - - - 4.53 17.62 None - - - - - -

AP-T - armor-piercing-tracer
FNH - flashless nonhygroscopic
f/s - feet per second
gr. - grain
HE - high-explosive
HE-T (SD) - high-explosive-tracer (shell destroying)
P.D. - point-detonating
perc. - percussion
TP-T - target-practice-tracer
* - Standard cartridge case is CASE, cartridge, 40-mm, M25. Substitute is M25B1, a steel case weighing 0.26 pounds less than the standard brass case.
# - Standard primer is PRIMER, percussion, M38A1. Earlier standards are: The M23A2 and the No. 12, Mk. II/L/ (British). Alternatives are: The M38B2 and Mk. 22 (Navy).
** - FUZE, dummy, M69; or inert FUZE, P.D., M64, M64A1, Mk. 27, 251 Mk. I, or other suitable types may be used.
% - Projectile has a tracer for observation purposes only.
*** - This shell has the Navy Shell-destroying Tracer Mk. 8 or Mk. 10.



260
 
110. PREPARATION FOR FIRING.

a. Charger clips loaded with rounds are ready for insertion in the automatic feed mechanism of the gun. Rounds packed in fiber containers, when removed therefrom, need only to be loaded in the charger clips.

111. DESCRIPTION AND DATA.

a. Data on the ammunition is given in table II which contains ammunition data. Additional information on components is given in the paragraphs below.

b. Armor-piercing Projectile. SHOT, AP-T, M81A1, is a steel projectile of the monobloc type. The body is solid except for a cavity in the base which holds the tracer composition. An ogival windshield is secured directly to the body of the shot by a 360-degree crimp. SHOT, AP-T, M81, is similar to the M81A1 Shot except that the windshield is attached to an adapter which is soldered to the body of the shot.

c. High-explosive Projectile. The body of SHELL, HE-T (SD), Mk. II, is a hollow steel casing with a conical nose and "boat-tailed" (conical) base. The nose and the base are threaded internally, the nose to receive the point-detonating fuze, and the base to receive TRACER and IGNITER, Shell, No. 12, Mk. I/L/; internal, or TRACER, M3. The No. 12' tracer, a British design, consists of a primer, an igniting charge, a red tracer composition, and a relay igniting charge. Functioning of the tracer is initiated by set-back upon firing. The tracer burns with a visible trace for about 7 to 10 seconds. As the tracer composition burns out, the relay igniting charge is ignited, detonating the bursting charge of the shell unless prior detonation has been caused by functioning of the fuze. In the M3 Tracer, a less complex type, the primer is omitted and the powder train is made up of one igniter charge, three charges of red tracer composition, and one relay igniting charge. Functioning is initiated by the propelling charge upon firing; the tracer then burns for 12 to 14 seconds. When fitted with the M3 Tracer, the shell is loaded with tetryl. Shells with the No. 12 tracer have a TNT filler. The bursting charge is approximately the same weight for all shells but the method of loading varies slightly for each model of fuze. This is necessary to provide a suitable charge cavity for the particular fuze assembled to the shell.

d. Cartridge Cases and Primers. CASE, cartridge, 40-mm, M25, or M25B1, is used in 40-mm ammunition of Army design. The M25B1 case differs from the M25 in that it is made of steel instead of drawn brass, has a thinner head and primer seat, and weighs approximately 0.26 pound less. The primer used in these cases is,



261
 
Figure 206 - Cartridge, HE-T (SD, M3), Mk. II, w/FUZE, P.D., M27 (Navy), 40-mm AA Guns
Figure 206 - Cartridge, HE-T (SD, M3), Mk. II, w/FUZE, P.D., M27 (Navy), 40-mm AA Guns


262
 
Figure 207 - Cartridge, TP-T, M91, w; FUZE, Dummy, M69, 40-mm AA Guns
Figure 207 - Cartridge, TP-T, M91, w; FUZE, Dummy, M69, 40-mm AA Guns


263
 
Figure 208 - Marking on Packing Box for Identification
Figure 208 - Marking on Packing Box for Identification


264
 
PRIMER, percussion, M38A1. Ammunition manufactured according to British design will be assembled with CASE, cartridge, M22, an adaptation of the British design. This case differs from the American standard case in that the primer hole is threaded to accommodate the threaded head of the British-type percussion primer, PRIMER, percussion, Q.F., cartridges, No. 12, Mk. II/L.

112. FUZES.

a. General. A fuze is a mechanical device used with the projectile to explode it at the time and under the circumstances desired. Fuzes which function on impact with a very light materiel target such as an airplane wing are known as supersensitive fuzes.

b. Boresafe Fuzes. Dependent upon the manner of arming, certain fuzes are considered to be "boresafe." A boresafe fuze is one in which the explosive train is so interrupted that, prior to firing and while the projectile is still in the bore of the cannon, premature action of the bursting charge is prevented, should any of the more sensitive elements malfunction.

c. FUZE,, P.D., Mk. 27 (Navy); FUZE, P.D., M71; FUZE, P.D., M64A1; FUZE, P.D., 251, Mk. I. These fuzes are designed for use with 40-mm antiaircraft ammunition. All are of the impact (point-detonating) type and are issued assembled to the projectile of the fixed complete round. The mechanical elements are so arranged that they function with superquick action on impact with relatively light materiel such as airplane surfaces. The fuzes are considered to be boresafe. However, FUZE, P.D., 251, Mk. I, arms by acceleration whereas FUZE, P.D., M71, and FUZE, P.D., M64A1, arm under rotational forces set up upon firing.

113. PACKING.

a. Data. The complete rounds are packed in two ways, in charger clips holding 4 rounds which in turn are packed in sealed watertight metal containers, and in individual fiber containers in wooden boxes. While weights of the individual rounds vary somewhat, dependent upon the type and model, the following data are considered representative for estimating weight and volume requirements:

Weight
(lb)
Volume
(cu ft)
In charger clips:
4 rounds per charger, 6 chargers (24 rounds) in metal packing box
Over-all dimensions of box (feet)
1.72 x 1.48 x 0.87
151 2.22
In fiber containers:
1 round per container, 24 containers (24 rounds) per wooden box
Over-all dimensions of box (feet)
1.83x 1.51x 1.13
159 3.12


265
 
b. Marking for Shipment.

(1) Packings for shipment are marked as follows:

(a) Name and address of destination or port officer (or code marking), preceded by word "To."

(b) Name and address of ultimate consignee, preceded by word "For." *

(c) List and description of contents. Packing boxes containing ammunition with M3 Tracer will have this model designation stenciled on the box to the right of the tracer insignia.

(d) Muzzle velocity of the rounds contained.

(e) Ammunition Identification Code (A.I.C.) symbol, as published in SNL's.

(f) Gross weight in pounds, displacement in cubic feet.

(g) The number of the package or shipping ticket.*

(h) The letters "U.S." in several conspicuous places.

(i) Order number or contract number.

(j) Ordnance insignium and escutcheon.

(k) Name or designation of consignor preceded by the word "From."*

(l) Lot number.

(m) Month and year packed.

(n) Inspector's stamp.

(2) In addition, the adhesive sealing strips on fiber containers are in the same color as the ammunition item, in accordance with the basic color scheme. It will be noted that for high-explosive projectiles the strips are yellow with black marking.

114. FIELD REPORT OF ACCIDENTS.

a. When an accident involving the use of ammunition occurs during training practice, the procedure prescribed in AR 750-10 will be observed by the ordnance officer under whose supervision the ammunition is maintained or issued. Where practicable, reports covering malfunctions of ammunition in combat will be made to the Chief of Ordnance, giving the type of malfunction, type of ammunition, the lot number of the complete rounds or separate-loading components, and condition under which fired.

Page 265 Continued in Next Part.


* - May be omitted on individual package in carload shipments of packages of standard weights and dimensions containing standard quantities.
 

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