3-INCH ANTIAIRCRAFT GUN MATÉRIEL, M2A2, M2A1, M1A2,

1. Purpose. The purpose of this manual is to furnish suitable

instructions for the maintenance and shop repair of the 3-inch anti-

aircraft gun matériel, M2A2, M2A1, M1A2, M1A1, T1A2, and T1A1.

It is for use of ordnance maintenance companies, civilian employees

of the Ordnance Department, Ordnance Reserve Officers' Training

Corps, National Guard, and Reserve officers charged with the main-

tenance and repair of this matériel.

2. Scope. This manual contains instructions for inspection, dis-

assembly and assembly, and maintenance and repair, supplementary

to those covered in TM 9-360. These operations should be conducted

in accordance with the procedure outlined in TM 9-1100. It also

describes and prescribes the use of special repair tools.

3. References. - The Appendix lists all Technical Manuals,

Ordnance Field Service Bulletins, Ordnance Proof Manual, Standard

Nomenclature Lists, drawings, and other publications relating to the

matériel described herein.

4. General. The tools for inspection and those pertaining to

maintenance and repair are issued as a set of special repair tools, and

are so listed in section IV, SNL D-14.

5. Tools for inspection. -The following tools are used in the

inspection of the gun and carriage by the ordnance maintenance

companies:

a. Sights, bore. - The bore sights are used in the verification and

adjustment of director firing system.

b. Ammeter. The ammeter is used in testing the electric current

at the brakes.

c. Gage, armature. The armature gage (fig. 11) is used when test-

ing the distance between the armature and the magnet of the electric

brakes.

d. Gage, tire. The tire gage is used when testing the pressure in

the balloon tires.

6. General. a. Inspection is for the purpose of determining the

condition of the matériel, whether repairs or adjustments are required,

and the remedies necessary to insure that the matériel is in serviceable

condition.

b. The use of the artillery gun book (O.O. Form 5825), is outlined

in the book. See also OFSB 4-1.

c. (1) The estimated average accuracy life in full service rounds of
the 3-inch antiaircraft guns, M1 and M3, is 2,500 rounds. The guns
in service will be star-gaged at approximately 10 percent and 90 per-
cent of their estimated average accuracy life in rounds fired, and
thereafter at each 10 percent during the remainder of their service.
Also, they should be star-gaged at any time an inspector may deem
it necessary on account of doubtful conditions, or when the bores show
signs of unusual wear or other irregularities. Decoppering of the
bores of cannon before star-gaging is prohibited. When star-gaging

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3-INCH ANTIAIRCRAFT GUN MATÉRIEL

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these guns the greatest distance from the muzzle at which star-gage measurements are to be made is 126 inches.

(2) For pastilles, or other defects of the bore of the guns requiring accuracy in measurement, plaster of paris should be used if practicable, as it gives a harder surface than gutta-percha and a more accurate measurement.

7. Inspection of gun and mount. -The inspection of the gun and mount and the instructions for inspection and verification of adjustment of director firing system as outlined in TM 9-360 should be followed. The following additional inspection of the mount and recoil mechanism should be adhered to:

a. Mechanism, recoil. -The recoil mechanism should be inspected as follows:

(1) The proper "full oil reserve" in this system is an amount equal to two oil screw fillersfull in excess of the quantity which can be poured into the recoil cylinder filling hole with the gun at maximum depression and proper gas pressure. With the recoil cylinder filled, any slight amount of reserve oil forced past the valve, A21027 (fig. 5), will force the floating piston away from the rear end of its cylinder and establish pressure in the oil side of the system to the extent of the nitrogen pressure present on the front face of the floating piston. To maintain this "system pressure" against periodical losses in reserve oil, the two oil screw fillersfull of reserve oil have been established as a proper amount for forcing the floating piston an appreciable distance away from its rearmost position. The expedient of forcing additional charges of reserve oil into the system to increase gas pressure is definitely prohibited.

(2) Remove the filling valve seat plug, A21185 (fig. 5), and examine for leakage. The valve should hold the pressure independently of the filling plug.

(3) Examine the buffer cylinder head follower for oil leakage. (4) Examine the extension piston and piston rod for unusual signs of wear or scored surfaces.

b. Equilibrator.-(1) Examine the seal around the gasket, A146977, and plug, A146981, of the gas filling valve (fig. 8) for gas leaks. With this plug removed, for attaching the nitrogen charging apparatus, a slight leak of gas through the valve, A138814, may be tolerated if it does not interfere with the connecting of the filling tube or reassembly of the plug. Extreme care should be observed when unscrewing filling valve plugs from charged mechanisms, as badly worn check valve gaskets will permit the pressure to build up against the plug. Such conditions will be evident if a continuous hiss of gas is heard through the threads as the plug is being unscrewed and also