40-mm Automatic Gun M1 (AA) and 40-mm Antiaircraft Gun Carriages M2 and M2A1, TM 9-252, 1944, is an Army technical manual for this widely used anti-aircraft gun of WW II. We offer this manual on the web site because it covers the single 40-mm gun used on many small ships. Note that the M1 gun is the same as found in the diverse mount manuals also on this site.
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40-mm Automatic Gun M1 (AA) and 40-mm Antiaircraft Gun Carriages M2 and M2A1
17 JANUARY 1944
RESTRICTED DISSEMINATION OF RESTRICTED MATTER-The information contained in restricted documents and the essential characteristics of restricted materiel may be given to any person known to be in the service of the United States and to persons of undoubted loyalty and discretion who are cooperating in Government work, but will not be communicated to the public or to the press except by authorized military public relations agencies. (See also paragraph 18b, AR 380-5, 28 September 1942.)
Washington 25, D. C., 17 January 1944
TM 9-252, 40-mm Automatic Gun MI (AA) and 40-mm Antiaircraft Gun Carriages M2 and M2A1, is published for the information and guidance of all concerned.
[A.G. 300.7 (27 Aug 43)
BY ORDER OF THE SECRETARY OF WAR:
G. C. MARSHALL, Chief of Staff.
J. A. ULIO, Major General, The Adjutant General.
DISTRIBUTION: R 9 (4); Bn 9 (2); IBn and H 44 (3); C 9 (8); IC 44 (5).
* This Technical Manual supersedes TM 9-252, dated 15 April 1942, including C1, dated 20 October 1942; TB 252-3, dated 13 July 1943; TB 252-4, dated 18 August 1943; TB 252-5, dated 28 October 1943; TC No. 54, dated 1943, section III, in part; and TB 252-6, dated 22 November 1943.
40-MM AUTOMATIC GUN MI (AA) AND 40-MM ANTIAIRCRAFT GUN CARRIAGES M2 AND M2A1
Section I INTRODUCTION
a. This Technical Manual is published for the information of the using arms and services.
b. In addition to descriptions of the 40-mm Automatic Gun M1 (AA) and the 40-mm Antiaircraft Gun Carriages M2 and M2A1, this manual contains technical information required for the identification, operation, inspection, and care of the materiel.
c. Disassembly, assembly, adjustment, and repair of the gun and carriage as may be handled by the using arm personnel are prescribed in this manual. They will be undertaken only under the supervision of an officer or the artillery mechanic.
d. Section X of this manual contains information required for the identification, operation, and care of the items of sighting and fire control equipment which are mounted directly on the gun and carriage. This section also prescribes authorized adjustments and repairs of this equipment. Other items of sighting and fire control equipment, not mounted directly on the carriage, are described in separate Technical Manuals. Refer to section XV for a list of these Technical Manuals.
e. Authorized ammunition for this weapon is described in section XI of this manual, which also provides information required for its identification, use, and care. Refer to section XV for a list of publications containing other pertinent information regarding the ammunition authorized for this weapon.
f. In all cases where the nature of the repair, modification, or adjustment is beyond the scope of the facilities of the unit, the responsible ordnance service should be informed in order that trained personnel, with suitable tools and equipment, may be provided, or proper instructions issued for the performance of the work.
g. This manual differs mainly from TM 9-252, 40-mm Automatic Gun MI and 40-mm Antiaircraft Gun Carriage M2, dated 15 April 1942, as follows:
(1) Information on the 40-mm Antiaircraft Gun Carriage M2A1 has been added.
(2) New lubrication charts have been added and lubrication instructions revised.
(3) Material on the Director M5 and the Generating Unit M5 has been deleted.
Figure 1 - 40-mm Automatic Gun MI (AA) and 40-mm Antiaircraft Gun Carriage M2A1 - Firing Position-High Elevation
(4) Information on the Computing Sights M7 and M7A1 has been added.
(5) Instructions on storage and shipment have been added.
(6) More complete instructions for operation under unusual conditions have been added.
a. The 40-mm Automatic Gun M1 (AA) fires fixed ammunition of armor-piercing and high-explosive types. It fires 1.93 to 2.06 pound shells in rapid bursts at a rate of 120 rounds per minute. The muzzle velocity is from 2,700 to 2,870 feet per second. The maximum effective range, limited by the director, is 3,000 yards.
Figure 2 - 40-mm Automatic Gun M1 (AA) and 40-mm Antiaircraft Gun Carriage M2 - Firing Position
Figure 3 - 40-mm Automatic Gun M1 (AA) and 40-mm Antiaircraft Gun Carriage M2 - Traveling Position
b. This gun is intended for duties intermediate between those of the high altitude guns of the 3-inch and 90-mm class and the cal. .50 machine gun. It is effective against dive bombers and low flying aerial targets. It may also be used against ground targets.
c. Most of the shells in the ammunition authorized for this weapon are equipped with tracer. The high-explosive shells are equipped with superquick fuzes which function on impact with a very light material such as an airplane wing. Bursting charges explode the shells unless prior detonation is caused by the functioning of the fuze. The complete rounds weigh from 4.49 to 4.82 pounds. They are loaded into the automatic loader of the weapon in clips of four.
d. The gun may be set on safe, single (semiautomatic) fire, or continuous (full automatic) fire. Cartridges are automatically placed in position for ramming. They are rammed when either of the two firing pedals on the carriage is depressed. The rammed cartridge releases the extractors, allowing the breechblock to close under the tension of the breech ring closing spring. After the breechblock is fully closed, the firing pin is automatically released to fire the piece.
e. The shock of recoil is absorbed by the recoil system which brings the gun to rest after recoil and restores it to battery (counter-recoil.) The action of recoil and counterrecoil provides the energy for opening the breech, ejecting the spent cartridge case, and reloading. Empty cartridge cases are ejected from the breech at considerable velocity and are directed toward the front of the weapon by a system of troughing.
f. The weapon may be traversed and elevated manually or by power. Manual control is by two double-handled cranks rotated by operators on seats on the carriage. Power control is by director. Traverse is continuous. The gun may be depressed and elevated from minus 6 degrees to plus 90 degrees. (In power operation, an elevating limit switch actuated by adjustable cam cuts off the power before the gun reaches the upper or lower limits of elevation, permitting it to drift to a stop. The cams are normally set to cut off the power at 0 degree and 85 degrees, respectively.) Spring type equilibrators facilitate elevation and depression of the weapon.
g. The 40-mm Antiaircraft Gun Carriage M2 is of the 2-axle, 4-wheel trailer type. A drawbar with a standard lunette forms the connection between the carriage and the prime mover. Spring suspension is arranged according to the Bofors parallelogram system which permits the wheels to spring independently of each other. The carriage is equipped with electric 4-wheel brakes operated from the prime mover and manually-operated mechanical rear wheel brakes. Combination taillight, stop, and blackout lights are provided.
h. The weapon is normally intended to be fired with the carriage
lowered to the ground with outriggers spread for stability, wheels raised, and chassis stakes emplaced. The axles are equipped with compensating springs to facilitate raising and lowering the carriage. Four screw-operated leveling jacks support the carriage in the lowered position and spirit levels are provided to insure correct leveling. Four chassis stakes are provided to anchor the carriage to the ground in the lowered position.
i. The gun may be fired from the wheels as may be necessary when the weapon is in convoy in combat areas. Under such conditions, the amount of traverse is dependent upon the manner in which the gun is prepared for action. Carriages of late manufacture, and earlier carriages so modified, are equipped with brackets which permit the outriggers to be locked in a traveling position so as to obtain unlimited traverse. The weapon is capable of being towed at high speed on good roads and at medium speed over bad roads and rough terrain.
3. DIFFERENCES AMONG MODELS.
a. While a number of minor changes and modifications have been made in the guns and carriages, the majority of these do not affect service of the materiel by the using troops.
b. Gun. Among the differences in the models of the guns which affect service by the using troops are the following:
(1) BARREL ASSEMBLIES. The barrel assemblies on certain of the guns are of Canadian and British manufacture. Their main difference is that the recuperator springs are made of Keystone (rectangular section) wire while these springs in barrel assemblies of United States manufacture are made of round wire. Threads on the parts of Canadian and British manufacture are metric threads; those on parts made in the United States are National Standard threads. Inasmuch as the interrupted threads at the breech end of the barrel, chamber, extractor grooves, rifling form and twist, and exterior and interior diameters are the same on all guns, all barrel assemblies are interchangeable.
(2) BREECHBLOCKS. The breechblock illustrated in this manual (fig. 12) has a removable firing pin bushing screwed into the front face and anchored by a locking pin. Breechblocks of later manufacture have a solid front face. The breechblocks are interchangeable.
(3) RECOIL CYLINDER FLUID. A blend of 60 parts by volume of OIL, hydraulic, and 40 parts by volume of OIL, recoil, light, are now used in the recoil cylinder in place of the glycerine-water mixture formerly used. The changeover to the new mixture is performed only by ordnance maintenance personnel. Cylinders filled with the new mixture are stamped on the front end: "OIL."
(4) REGISTER MARK ON GUN TUBE. A lateral machined mark is cut into all gun tubes produced since June 1943. This register mark (fig. 6) is located just to the rear of the flash hider at the bottom of the center line of the tube. It is for convenience in alining the barrel assembly for removal and installation, particularly in the dark.
(5) COOLING SLOTS IN FORE PORTION OF BREECH CASING. Cooling slots are provided in the fore portion of the breech casings of all guns of early manufacture. These slots are eliminated in guns of later manufacture (fig. 9).
c. Carriages. Among the differences in the models of the carriages which effect service by the using troops are the following:
(1) 40-MM GUN CARRIAGES M2 AND M2A1. The two carriages have different gear ratios in the hand traversing mechanisms. The gear ratio of the hand traversing mechanism of the 40-mm Gun Carriage M2A1 is approximately three times as high as that of the 40-mm Gun Carriage M2. The rate of traverse per turn of the crank of the M2A1 Carriage is 17 1/7 degrees; of the M2 Carriage, 6 degrees. The principal differences between the hand traversing mechanisms of the two carriages are a larger hand traversing mechanism gear case and long and short traversing mechanism bevel gears of higher ratio on the M2A1 Carriage.
(2) OUTRIGGER EXTENSION BRACKETS. On carriages of late manufacture, and on those so modified, chassis frame outrigger extension brackets with double outrigger hooks (insert, fig. 53) are welded to both sides of the front chassis frame girder. When the outriggers are folded and engaged by the ends of these brackets, continuous traverse of the top carriage is permitted when the weapon is in traveling position. On unmodified carriages of early manufacture, the outriggers, when folded, are engaged by hooks welded directly to the front chassis frame girder; traverse is restricted when the weapon is in traveling position.
(3) OUTRIGGER HINGE COVERS. On carriages of early manufacture, the outrigger hinges were protected by welded steel outrigger hinge covers which were fitted over them when the weapon was placed in traveling position. Canvas outrigger hinge covers are currently being supplied for this purpose.
(4) SAFETY SWITCH AND DUMMY SOCKET. On carriages of earlier manufacture, the electric brake safety switch, together with the dummy socket for the jumper cable, are located on a bracket mounted on the steering drawbar link. On carriages of later manufacture, and on those so modified, the safety switch is mounted on the steering drawbar link but the dummy socket for the jumper cable is mounted on the side of the drawbar (fig. 69).
(5) STRAPS AND CLIPS. On carriages of late manufacture, and on those so modified, web straps and chassis clips are provided to secure the front and rear chassis compensating spring lock handles
in locked position and prevent them from becoming unlocked accidentally.
(6) WHEELS. Some carriages are equipped with wheels of the flat base rim type (fig. 72); others are equipped with wheels of the divided rim type (fig. 73).
(7) TIRES. The standard tire equipment is the 6-ply, heavy-duty, truck-bus type tire with standard heavy-duty tube and flap. Carriages of early manufacture were equipped with 6-ply, heavy-duty, truck-bus type tires and heavy bullet-resisting tubes. Some carriages were equipped with combat tires.
(8) AZIMUTH INDICATORS. Azimuth indicators with two types of faces have been used, the "match the pointer" type (fig. 177) and the "red-black-white (blackout)" type (fig. 178). The majority of the latter have been modified by having their dials painted all black except for alining marks, making them similar to the match the pointer type.
(9) SIGHTS. Weapons are equipped with Sighting System M3 (fig. 161) or the Computing Sight M7 (fig. 162).
a. General Data Pertaining to the 40-mm Automatic Gun M1 (AA):
Weight of barrel assembly
Weight of tipping parts
Type of breechblock
40-mm or 1.573 in.
148.25 cu in.
0.051 per in.
29.9 cu in.
Number of grooves
Depth of grooves
Width of grooves
Twist, nonuniform, increasing from one turn in 45 calibers at the breech to one turn in 30 calibers at the muzzle.
Weight of projectile
1.93 to 2.06 lb
Weight of propelling charge
0.65 to 0.72 lb
Weight of complete round
4.49 to 4.82 lb
Length of complete round
17.60 to 17.62 in.
High-explosive or armor-piercing
2,700 to 2,870 ft per sec
Time of flight at 1,500 yards
Range (maximum effective, limited by director)
Type of fire
Single fire or automatic
Rate of fire, rapid bursts
120 rounds per min
Capacity of magazine
Capacity of cartridge clips
7.4 to 8.3 in.
Protrusion of firing pin
0.099 to 0.114 in.
b. General Data Pertaining to the 40-mm Antiaircraft Gun Carriages M2 and M2A1:
Weight of carriage with oil gears
Weight of complete weapon with accessories
55 3/8 in.
Over-all length (traveling)
18 ft 9 1/2 in.
Over-all width (traveling)
6 ft 0 in.
Over-all height (traveling)
6 ft 7 1/2 in.
Over-all height (firing, maximum elevation)
13 ft 9 in.
Minimum turning diameter
14 1/8 in.
(Power cut-off by elevation limit switch for director control normally set at 85 degrees)
Maximum depression, top carriage level
(Power cut-off by elevation switch for director control normally set at zero degree)
Amount of traverse
360 deg continuous
Rate of traverse per turn of crank:
17 1/7 deg
Rate of elevation per turn of crank
45 lb per sq. in.
a. Before initial loading of the weapon, the outer safety lever should be placed in the "SAFE" position.
b. For safety, when the breech is open and the gun is not to be fired, always place the hand operating lever 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.
c. 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 front 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.
d. There will be some movement of the carriage, generally in a backward direction, as the carriage is being lowered into firing position. 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 the front and rear leveling jacks will drop on them as the carriage is being lowered.
e. After the carriage has been lowered, the drawbar and gun stay must be held securely until the chassis compensating spring lock
handles have been engaged. Ease the carriage into its lowered position; do not drop it.
f. When the weapon is in firing position, the gun stay handle
plungers should always be released so that the gun stay is loose on the axle.
g. Close and lock the top cover before firing.
h. Do not exert excessive force on the cartridge remover, for damage to the feed rollers will result.
i. Under no circumstances will the chassis compensating spring lock 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.
j. 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 front and rear leveling jacks.
k. In traveling, 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.
l. Lubricate after washing gun and carriage. Do not use high-pressure
washing system for cleaning artillery materiel.
m. Do not allow moisture, dirt, or grit to enter any mechanism or compartment when lubricating, adjusting, inspecting, disassembling, or assembling any part of the weapon.
n. For lubrication, care, and maintenance instructions for use under unusual conditions, refer to section XIV.
o. Do not attempt to remove the barrel assembly unless the breech is open or the breechblock has been removed from the breech ring. To do so will damage the extractors and produce burs in the extractor grooves in the breech end of the barrel.
p. In carrying the barrel assembly, keep it on an even keel. If the muzzle end is raised, there is a possibility that the barrel assembly will become detached from the barrel carrier, permitting the breech of the barrel to strike the ground.
q. Before removing the barrel assembly, be sure that the top cover remains in locked open position and that the breechblock locking pin is in its place in the holes in the breech casing and breech ring. These devices prevent the breech ring and automatic loading tray from moving to the rear after the barrel assembly has been removed.
r. When placing the automatic loader on a flat surface after its removal from the breech casing, great care must be taken to avoid damage of parts. A slight tilting movement at the time of contact may result in such damage.
s. Do not allow any grease or SOLVENT, dry-cleaning, to touch the brake lining or magnet.
t. (Divided rim type wheels) Completely deflate tires before attempting to remove wheel flange retaining nuts. An inflated tire may blow a partially removed flange off the wheel and cause serious injury to personnel.
u. (Flat base rim type wheels) Tap the locking ring during the initial inflation of the tire to seat it firmly in the rim well. Stand aside while inflating the tire to avoid personal injury in case the locking ring is not properly seated in the rim well and flies off the wheel.
v. Disassembly and assembly of Computing Sights M7 and M7A1 by the using arm personnel 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.
w. Keep the Computing Sights M7 and M7A1 clean and in condition for traveling when not in use, the telescopes in their cases and the canvas covers in place.
x. The following precautions should be taken in the operation and maintenance of the Remote Control System M5:
(1) The elevation limit switch must be "OFF" before engaging or disengaging elevation clutch.
(2) Be particularly careful when orienting in elevation that elevation motor switch at the director is "OFF." Otherwise, a super-elevation will be set in, and orienting will be in error by amount of superelevation.
(3) Power should be switched off before cables are connected or disconnected. See that cables are securely held in receptacles before turning power on.
(4) The elevation clutch lever should be put in the "IN" position (top of lever away from coupling) before switching on the power supply.
(5) Never put oil from an unsealed container in oil gears.
(6) Be sure that oil gears have been filled with oil correctly as noted in paragraph 102.
(7) Be sure carriage is level before firing. Correct leveling of carriage cannot be overstressed.
(8) In orienting for elevation or in adjusting oil gears to neutral, 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, units should be protected to insure that no dust or rain gets into unit.
(9) Adjustment of backlash in transmitter gearing should be made only by qualified battery electrician.
(10) Do not turn either adjusting screw more than several turns, as otherwise the mechanism may become disengaged.
(11) Exercise care in handling the pilot valve. Do not touch valve proper with hands, as dirt and perspiration are detrimental to it. While valve assembly is out of oil gear, wrap it in a piece of clean paper and keep it in a safe place so as to prevent burring or scratching.
(12) Be sure tube for inserting pilot valve is absolutely clean before using. Clean with SOLVENT, dry-cleaning.
(13) Oil gears must be kept level at all times in order to prevent oil from entering electrical units above oil gear motors.
(14) Do not under any circumstances pull bell housing off motor. If this is done, the rear motor bearings will fall out and replacement of bearings will necessitate use of a special tool which is not issued to using arms. The bell housing is rotated to enable fastening upper portion of oil gear unit to carriage (bell housings which are equipped with two brackets need not be rotated).