a. This section outlines the operation of the weapon and carriage. It prescribes precautions to be taken for the protection of the personnel and materiel. Many of the operations described herein will be performed simultaneously. This section is not to be construed as a Field Manual on the service of the piece.
36. TO OPERATE BREECH MECHANISM.
a. To Open Breech.
CAUTION: Prior to opening the breech, place the outer safety lever in the "SAFE" position.
(1) BY HAND. Release the hand operating lever from the front latch bracket by pushing the handle inwardly toward the breech casing against spring action and lifting the handle to clear the holding catch. Lift the hand operating lever and pull it up and to the rear as far as it will go (fig. 76).
CAUTION: For safety, when the breech is open and the gun is not to be fired immediately, always place the hand operating lever
Figure 76 - Opening Breech With Hand Operating lever
Figure 77 - Closing Breech With Outer Extractor Releasing Lever
Figure 78 - Unlimbering the Weapon
Figure 79 - Locking Drawbar and Steering Yoke
in its rear latch bracket where the lever will be in vertical position and the breechblock will be held in open position. With the hand operating lever in this position, the weapon cannot be fired.
(2) AUTOMATICALLY. The functioning of the breech operating mechanism in automatic operation is described in paragraph 11 c. The hand operating lever must be released from the rear catch bracket, folded forward, and housed in the front latch bracket, for automatic loading and firing.
b. To Close Breech.
(1) BY HAND. Release the hand operating lever from the rear latch bracket and draw it to the rear to lower the breechblock slightly to take the tension off the cartridge case extractors. While doing so, press the outer extractor releasing lever rearward (fig. 77). Allow the hand operating lever to go forward easily so the breechblock will not slam shut. These operations free the breech ring outer crank to rotate, release the cartridge case extractors from the breechblock, and permit the closing spring to raise the breechblock to closed position.
(2) AUTOMATICALLY. The functioning of the breech operating mechanism in automatic operation is described in paragraph 11 c.
37. TO PLACE WEAPON IN FIRING POSITION.
a. Maneuver the weapon into position on approximately level ground with the prime mover.
b. Detach the safety chain from the prime mover and wrap it around the break-away safety switch. Disconnect the jumper cable and insert the plug in the dummy socket. Disconnect the drawbar lunette from the pintle of the prime mover (fig. 78). Unload the prime mover and remove it from the vicinity of the weapon.
Figure 80 - Unlocking Steering Lock
Figure 81 - Removing Outrigger, Carriage, and Sight Covers
c. Lock the drawbar, steering link, and front axle yoke into one rigid lever. Remove the drawbar steering link pin from its bracket and insert it through the vertical holes near the front of the steering yoke and near the rear of the steering link (fig. 79). The drawbar may have to be raised and slightly moved from side to side to mate the holes. Lower the drawbar to aline holes and insert the drawbar pin through the holes near the rear of the right side of the drawbar and near the front of the right side of the steering link.
Figure 82 - Locking Outrigger in Outward Position
Figure 83 - Unlocking Gun Stay and Elevating Gun
d. Unlock the steering lock by rotating the handles (fig. 80) and swing the steering lock link forward out of its recess in the front of the front chassis swivel.
e. Remove outrigger hinge covers. Unlock the outriggers by rotating the outrigger eccentric hinge levers toward the rear of the carriage until they contact the lever stops. Swing the outriggers slightly outward to release the bottom of the carriage cover. Remove the carriage cover and the right and left sight covers (fig. 81). Check to see that the power synchronizing mechanism handle is in the disengaged or upward position.
f. Swing the outriggers to fully open position and lock them in
Figure 84 - Unlocking Rear Chassis Compensating Spring Lock
Figure 85 - Unlocking Front Chassis Compensating Spring Lock
place by returning the outrigger eccentric hinge levers to their initial positions (fig. 82).
g. Unlock the gun stay from the gun by rotating the gun stay plunger handles and locking plunger handles (fig. 83). Elevate the gun to at least 40-degree elevation.
h. Release the hand brakes if they have been set. Check the leveling jacks to make certain that they are not extended. Unbuckle the safety straps which secure the front and rear chassis compensating spring lock handles. With two men holding the drawbar and two men holding the gun stay, unlock the front and rear axles by unlatching and lifting the front and rear lock handles (figs. 84 and 85).
CAUTION: The safety straps should be fastened at all times, except when the front and rear chassis compensating spring lock handles are used to unlock the axles. The axles should never be unlocked unless there are two men to hold the gun stay and two men to hold the drawbar. The locks should be released simultaneously, and the gun stay and the drawbar must be held securely while the locks are being released.
i. Using the drawbar and gun stay as levers, rotate the axles until the carriage is lowered onto the foot plates of the leveling jacks (fig. 86). In performing this operation, the men at each end of the weapon must rotate the axle trees simultaneously. If this is not done, the balancing mechanism will not perform satisfactorily. To prevent injury to personnel, it is advisable that the carriage be lowered to the lowest position possible. If this is done, there is less likelihood of unexpected movement of the carriage when the chassis compensating spring lock handles are released in preparation for raising the carriage to traveling position. There are several positions in which the front and rear axles may be locked.
CAUTION: There will be some movement of the carriage, backward or forward, as the carriage is being lowered. Care should be taken that all members of the crew keep their feet in such positions that there is no possibility that the foot plates of front and rear leveling jacks will drop on them as the carriage is being lowered.
j. While the drawbar is being held vertically (fig. 87) and the gun stay is being held horizontally (fig. 88), relock the axles by returning the lock handles to their original positions. If the lock handles do not rotate easily into their locked positions, it will be necessary to raise or lower the chassis by slightly moving the gun stay or drawbar back and forth until the axles have been rotated into positions which will permit the lock handles to be returned to their locked positions. Do not force lock handles, as breakage of parts will result.
CAUTION: The drawbar and gun stay must be held securely until the lock handles have been locked. Ease the carriage into its lowered position; do not drop it.
k. Level the weapon by means of the four leveling jacks and the level assemblies mounted on the top carriage frame base (fig. 89). Do not use levels which may be mounted on the outer extremities of the chassis frame. The carriage should be leveled as close to the ground as possible. To level the weapon on relatively even ground, place the foot plates of all the leveling jacks in contact with the
Figure 86 - Lowering Carriage to Firing Position
Figure 87 - Relocking Front Chassis Compensating Spring Lock
Figure 88 - Relocking Rear Chassis Compensating Spring Lock
ground. Raise each jack three full turns of the jack handle to bring all wheels off the ground. Using the two levels mounted on the top carriage frame base and two adjacent jacks at right angles to one another, level the weapon.
l. Withdraw the drawbar pin from the holes in the right side of the drawbar and steering link, drop the steering lock link downward, and fold the drawbar downward to the horizontal position (fig. 90). Place the drawbar pin in the hole in the top of the drawbar. Unlock the gun stay from the rear axle and let it rest on its support.
CAUTION: When the weapon is in firing position, the gun stay
Figure 89 - Leveling Weapon
Figure 90 - Folding Drawbar to Horizontal Position
Figure 91 - Removing Chassis Stake
Figure 92 - Driving Chassis Stake
handle plungers should always be released so that the gun stay is loose on the axle.
m. Remove the four stakes by pushing their pointed ends against the spring-loaded plungers and lifting their heads from the retaining brackets (fig. 91). Insert the stakes in the double brackets provided for them on the chassis and outriggers (fig. 92). Using the maul, drive the stakes firmly into the ground as far as they will go.
NOTE: If the front stake cannot be driven into the ground to the point where it will not interfere with the traversing of the weapon, remove it entirely. In driving the front stake, care must be taken not to damage the break-away safety switch. This may be done by using a drift, after the stake has been started.
Figure 93 - Adjusting Control Rod Valve
n. After the stakes have been driven into the ground, check the level of the weapon in the original leveling position and for full traverse at 90-degree intervals. Make any necessary corrections. If the weapon cannot be leveled for 360-degree traverse with the level assemblies mounted on the base of the top carriage, check the level of the weapon with a gunner's quadrant. Place the gunner's quadrant on the machined portion of the breech casing and check with the gun in four positions with 90 degrees of traverse between each reading. If the levels are found to be out of alinement, adjust the faulty level as soon as conditions will permit.
o. The double crank handles of the elevating and traversing hand drive mechanisms should be attached at all times, but they should remain in the disengaged position unless the weapon is being manned for direct fire sight control.
38. TO CHECK LIQUID IN RECOIL CYLINDER.
a. Elevate the gun to 25 degrees. Remove the filling plug from the recoil cylinder and note whether the liquid is up to the level of the filling plug. If the cylinder is not filled to the proper level, follow the procedure for filling outlined in paragraph 66 c.
b. To Adjust Recoil Cylinder Control Rod Valve. Remove recoil cylinder control rod valve spindle adjustment screw and plate. Turn the squared end of the control rod valve spindle (fig. 93) to close the control rod valve fully; then back off the spindle one-third turn. Lock the spindle with the adjustment screw and plate. A further slight adjustment may be necessary after the gun is fired.
39. TO TRAVERSE.
a. By Hand. The weapon is traversed by turning the double
Figure 94 - Traversing Weapon
hand crank on the right side of the gun (fig. 94). A seat and footrests are provided for the operator who moves in azimuth with the gun. Turning the crank clockwise traverses the gun to the left. Traverse is continuous. On the Gun Carriage M2, one turn of the crank moves the gun approximately 6 degrees in azimuth. Approximately 58 turns of the crank are required to traverse the top carriage 360 degrees. On the Gun Carriage M2A1, one turn of the crank moves the gun approximately 17 degrees in azimuth. Approximately 21 turns of the crank are required to traverse the top carriage 360 degrees.
b. Rapid Traverse. Pulling up on the handle of the power synchronizing mechanism (slewing handle) disengages the traversing power drive and permits the top carriage to be swung around (slewed) rapidly (fig. 95). This lever must be depressed to engage the traversing power drive and permit the top carriage to be moved in azimuth by the director.
c. By Power. To permit the weapon to be traversed by the director the hand drive traversing mechanism must be disengaged by pulling the double hand crank out of mesh (away from the gun), and depressing the handle of the traversing power drive (slewing handle) to engage the traversing power drive.
40. TO ELEVATE.
a. By Hand. The gun is elevated by turning the double hand
Figure 95 - Rapid Traverse - Slewing Gun
Figure 96 - Elevating Weapon
crank on the left side of the gun (fig. 96). A seat, footrests, and a firing pedal are provided for the operator who moves in azimuth with the gun. Turning the crank clockwise elevates the gun. The maximum elevation is 90 degrees. The maximum depression is minus 6 degrees. One turn of the crank elevates the gun approximately 4 degrees.
Figure 97 - Removing Flash Hider Cover and Automatic Loader Hood and Shield
b. By Power. To permit the gun to be elevated by the director, the hand drive elevating mechanism must be disengaged by pulling the double hand crank out of mesh; then the elevation oil gear clutch must be shifted to "on" position, if it is not already in that position, and finally, the elevating limit switch must be placed in "on" position. Maximum power elevation and depression are limited by the setting of the limit switch and are approximately 85 degrees and zero degree, respectively.
41. PRIOR TO FIRING.
a. If conditions permit, check the level of the liquid in the recoil cylinder (par. 38 a). Check the adjustment of the control rod valve (par. 38 h). Inspect the recoil cylinder for oil leakage.
CAUTION: Close and lock the top cover before firing.
b. Make certain that the breech casing top cover is closed and locked securely. Serious damage will be done by firing the gun with the top cover open. Not only is the barrel assembly unlocked and free to turn in the breech ring when the top cover is open, but the breech ring is locked in position in the breech casing by the breech ring barrel catch control arm. When the gun is fired with the control arm in this position, the arm is sheared off and jammed between the breech ring and breech casing.
c. Make certain that the director, carriage stakes, or any other part of the materiel does not interfere with the traversing of the weapon.
d. Just prior to loading and firing the gun, remove the flash hider cover and the automatic loader hood and shield (fig. 97). These covers should be in place as much of the time as possible to protect the bore and loader from dirt and other foreign matter. Check to make
Figure 98 - Inserting Clip Into Automatic Loader
sure that the outer safety lever is in the "SAFE" position. Inspect the bore for foreign matter and clean if necessary. If conditions permit, wipe or clean the bore to remove the coating applied after the previous firing.
42. TO LOAD.
a. Pull the hand operating lever at the left side of the breech casing to the rearmost position and engage it in the rear latch bracket. This operation opens the breech, cocks the firing mechanism, pulls the rammer shoe to the rear where it is engaged, and releases the feed rollers to permit them to be rotated.
b. Place a cartridge on the loading tray by pushing a clip of ammunition down the guides of the loader (fig. 98) until the feed rollers are rotated and a cartridge drops on the loading tray.
c. If the gun is not to be fired immediately, the hand operating lever should remain in the rear latch bracket to make the gun safe against accidental firing.
d. To Load Ammunition in Clips. Press the spring-loaded pin on the side of the clip (fig. 99). Insert the rim of the cartridge in the proper one of the four concave depressions of the clip. Release the pin to permit the hook to clamp the cartridge in place in the clip.
43. TO FIRE.
a. Immediately before firing is to take place, the hand operating lever must be folded forward and placed in the front latch bracket. The outer safety lever must also be in "SINGLE FIRE" or "AUTO FIRE" position before firing can occur.
Figure 99 - Loading Cartridge in Clip
Figure 100 - Firing Weapon With Rear Firing Pedal
Figure 101 - Recoil Indicator Set to Measure Length of Recoil
Figure 102 - Loading Tray Striking Indicator To Measure Recoil
b. The firing mechanism is actuated by either of two controls. The front firing pedal is located above the elevation operator's right footrest on the left side of the weapon. The rear firing pedal is located near the rear of the loading platform on the left side of the breech (fig. 100).
c. To fire the gun, either pedal is depressed. With the outer safety lever set at "SINGLE FIRE," the pedal must be depressed to fire each round separately. With this lever set at "AUTO FIRE," the gun will continue firing as long as the pedal is depressed and there are more than two rounds in the automatic loader.
44. OBSERVATION DURING FIRING.
a. Observe the movement of the weapon in recoil and counterrecoil. Movement should be smooth and the end of movement in both directions should be without shock. During action, the operation of the recoil system should be watched carefully and necessary corrective measures must be taken to insure that the weapon will not be forced out of action due to malfunction of the recoil system. Examine the recoil cylinder at intervals during fire to be sure that there is no leakage of liquid.
b. Measure Length of Recoil.
(1) Measure the length of recoil for the first round and at intervals during firing, when practicable. The normal length of recoil is from 7.4 to 8.3 inches. The most desirable length is 7.87 inches. Excessive recoil will cause damage to the mechanism. Short recoils will prevent the effective working of the automatic loader.
(2) To measure the length of recoil, press the lower arm of the
Figure 103 - Inserting Cartridge Remover
recoil indicator pointer (fig. 101) forward, causing the pointer to register "60" (6 in.) on the recoil indicator scale plate. When the piece is fired, the rear end of the loading tray will strike the lower arm of the indicator pointer in recoil (fig. 102). The pointer will indicate the farthest backward movement of the tray. Read the measurement on the scale plate which is calibrated in tenths of inches from 6 to 9 inches.
(3) If the length of recoil does not fall within the limits designated, take corrective measures at once (par. 53).
c. Control Speed of Counterrecoil.
(1) The counterrecoil of the gun has an important bearing on the steadiness and service of the weapon. A violent counterrecoil will cause undue shock to the carriage; a slow counterrecoil will result in slow firing. Both are to be avoided.
(2) The squared head of the control rod valve spindle, which protrudes from the front end of the recoil cylinder, provides a means for adjusting the speed of counterrecoil. The setting of this spindle should be checked before firing is commenced, to see that the control rod valve is opened one-third turn of the spindle. If the speed of counterrecoil is unsatisfactory, the setting of this spindle should be adjusted to correct the condition (par. 38 h). The valve should be closed slightly if the speed of counterrecoil is too great; it should be opened slightly if the speed is too slow.
(3) It will be noted that the gun can counterrecoil more easily when it is at a lower elevation because the effect of gravity on the gun is lessened. Watch for too severe counterrecoil when the gun is fired at lower elevations. Report any irregularity of operation at once.
Figure 104 - Raising Cartridges Into Cartridge Remover
Figure 105 - Removing Cartridges From Automatic Loader
45. TO UNLOAD.
a. Before attempting to unload the gun, place the outer safety lever in "SAFE" position and elevate the gun to about 30 degrees. Pull the hand operating lever all the way back past the rear latch bracket. A man at the rear of the gun should reach in through the opening in the rear cover and catch the round as it slides out of the firing chamber as the lever is being pulled backward.
b. The rounds in the automatic loader are removed with the cartridge remover, which depresses the feed and stop pawls. Insert the remover into the loader (fig. 104) until the top of the remover is flush with the top of the feed and stop pawl holder frame.
CAUTION: Do not exert excessive force on the cartridge remover, for damage to the feed rollers will result.
c. With the aid of the shell pusher, manipulated through the opening in the rear cover, work the cartridges up into the remover and lift the cartridges and remover through the top of the loader (fig. 105).
d. With the hand operating lever still in the extreme rearward position, trip the extractor releasing lever at the right front of the breech casing. The breechblock is then free to be raised by the action of the breechblock closing spring, the movement being controlled by moving the hand operating lever to its forward (horizontal) position.
e. Place the feed control thumb lever to the right-hand position. Step on the firing pedal to release the rammer. The gun is now unloaded and uncocked.
Figure 106 - Withdrawing Carriage Stakes From Ground
f. Cartridge Case Removal With Hand Cartridge Extractor.
(1) If the cartridge case sticks in the chamber and cannot be removed in the normal manner, it should be pried out with the hand cartridge extractor.
(2) Open the breech. Open the top cover. Insert the hand cartridge extractor through the upper opening of the breech casing into the aperture in the breech end of the tube. Engaging the rim of the cartridge case with the extractor, carefully pry the case out of the chamber. Check the condition of the extractors in the breech ring to determine the cause of the faulty extraction. Also check the firing chamber for pitting or excessive foreign material.
g. Cartridge Case Removal With Hand Shell Ejector.
(1) If the cartridge case cannot be removed in the normal manner or with the hand cartridge extractor, or if the case separates from the projectile, the round or the projectile should be removed with the hand shell ejector.
(2) Place the weapon at zero elevation. Open the breech. Assemble the cleaning staff M14. Screw the hand shell ejector onto the end of the assembled cleaning staff. Insert the ejector into the muzzle of the gun and push the round back onto the loading tray. Make a thorough check of the firing chamber and extractors to determine the cause of the malfunction.
46. TO PLACE IN TRAVELING POSITION.
a. Withdraw the carriage stakes from the ground by inserting the end of a crowbar in successive holes in the rear of the stake, prying the stake from the ground (fig. 106).
b. Raise the drawbar to vertical position and insert the drawbar pin in the holes in the drawbar and steering link. Lock the gun stay to the rear axle by means of the gun stay handle plungers.
c. Raise the leveling jacks to place all four wheels of the carriage in contact with the ground. If due to rough or sloping terrain holes have been dug beneath the wheels for emplacing, these holes must be refilled if necessary to insure that the wheels are actually on the ground. After the leveling jacks have been raised to traveling position, check to see that the jack handles are in locking notches which face directly away from the gun; otherwise, difficulty will be experienced in rotating the gun stay and drawbar when the carriage is being raised.
CAUTION: Under no circumstances will the locking handles which lock the front and rear axles be unlocked unless the carriage wheels are in solid contact with the ground. Failure to observe this precaution is likely to result in serious injury to battery personnel.
NOTE: The effort of raising the carriage from firing to traveling position is aided by the strong chassis compensating springs in the front and rear girders. They operate by pushing the wheels against the ground. If the lock handles are rotated before the wheels are lowered to the ground, the force of the compensating springs is released to rotate the axles violently. The result will be that personnel in the way of the drawbar or gun stay will be injured.
d. With the carriage wheels on the ground, and the gun stay and drawbar held tightly to resist any unexpected movement, unlock the front and rear axles by rotating the lock handles.
e. Using the drawbar and gun stay as levers, rotate the axles to raise the carriage to traveling position. Raise both ends of the carriage at the same time, or raise the rear end first. Raise the carriage as gradually as circumstances permit to prevent it from "bouncing" into traveling position.
CAUTION: Do not stand directly in the path of the drawbar or gun stay until the carriage has been securely locked in traveling position. Keep feet from under the foot plates of the front and rear leveling jacks.
f. Lock the axles in traveling position by rotating the lock handles. Lock the steering link securing clamp. Depress the gun, unlock the gun stay from the rear axle, and lock the gun stay to the breech casing. Disengage the traversing and elevating double hand cranks by pulling them outwardly from the gun; leave them attached to the weapon. Remove the drawbar steering link pin and place it in its bracket. Remove the drawbar pin and place it in the hole in the top of the drawbar.
Figure 107 - Weapon in Traveling Position - Covers in Place
g. After replacing the carriage cover and right and left sight covers, unlock, close, and lock the outriggers. Replace the outrigger hinge covers (fig. 107).
h. Back up the prime mover until the drawbar lunette can be placed over the pintle of the prime mover. Connect the jumper cable and. safety chain. Make sure that the safety chain is not connected in such a manner as to cause the brakes to function on a sharp turn; leave sufficient slack to prevent this from happening.
47. BRAKE OPERATION.
a. When applying the brakes for an ordinary stop, the handle of the controller on the prime mover should be advanced gradually for a light brake operation. Heavy brake application should be reserved for emergency stops and should not be employed in ordinary brake service.
b. The load control on the controller is provided to permit the driver to regulate the braking power and prevent skidding regardless of load and road conditions. For slippery roads, the control should be set on "LIGHT."
c. When applying the brakes for a slowdown or stop, always apply the brakes on the load before applying the brakes on the prime mover.
d. When the speed of the prime mover is above the idling speed of the engine, leave the engine in gear and close the throttle. This will permit the engine to function as a brake. When the speed of the vehicle corresponds to the idling speed of the engine, throw out clutch and gradually apply brake.
e. When brakes are new, several applications must be made before maximum efficiency is obtained, because the magnet must wear grooves in the armature to insure proper contact.
CAUTION: To avoid injury to the personnel, to insure safe road transportation, and to prevent "jackknifing" of the load, the driver should have the load under control at all times by avoiding any slack between the load and the prime mover. On down grades, curves, and rough or slippery roads, the speed should be held to approximately 10 miles per hour.