M4 cannon

The 37 mm Automatic Gun, M4, known as the T9 during development, was a 37 mm (1.46 in) autocannon designed by John Browning and used in the Bell P-39 Airacobra and P-63 Kingcobra fighters, as well as experimentally on other designs. It provided interceptor with a weapon that could shoot down any bomber with as little as one hit. It was a compact design with a relatively low muzzle velocity and rate of fire.

Design

Designed primarily as an anti-aircraft weapon, the gun had a muzzle velocity of and a cyclic rate of 150 rounds per minute. It was normally loaded with high-explosive shells, but could also be loaded with the M80 armor-piercing shell, which could penetrate 1 in (25 mm) of armor plate at . It was magazine-fed and could be fired manually or by remote control through a solenoid mounted on the rear of the gun.

Recoil and counter-recoil were controlled hydraulically by means of a piston and spring combination connected to the recoiling parts and operating in an oil-filled recuperator cylinder mounted to the stationary trunnion block assembly. The recoiling parts of the gun included the tube and tube extension, the recuperator piston and piston rod, the lock frame assembly, the driving spring assemblies, and the breechblock assembly. The nonrecoiling parts included the trunnion block group, the feed box and feeding mechanism, the recuperator cylinder and bushing, the back plate group, and the manual charger...
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