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Browning Model M4 (T9)
37 mm Cannon
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    The 37 mm (1.46 in) M4 Automatic Cannon was a compact, low velocity and rate-of-fire auto-cannon developed by Browning in 1921. Browning and the Colt Firearms Co reworked it into the T9/M4. It was designed primarily as an anti-aircraft weapon and used in the Bell P-39 Airacobra and P-63 Kingcobra fighters, as well as experimentally on other designs. It provided interceptors with a weapon that could shoot down almost any airplane with as little as one hit. The gun was magazine-fed and the normal round was a high explosive shell, but this could also be substituted for a M80 armor-piercing shell which could penetrate 1 inch armor plate at 500 yds. It was fully automatic when the trigger was pulled and would continue to fire until the magazine was empty. The rate of fire was 125 to 150 RPM and the muzzle velocity was 2,000 ft/s (610 m/s). The magazine could be fed with a 15 or 30-round endless belt, but the 30-round endless belt was used exclusively in production models which would give a firing time of twelve to fourteen seconds.

    The recoil and counter-recoil were controlled hydraulically by a piston and spring mechanism which was mounted on a fixed stationary trunnion block assembly. The gun had to fire as smooth as possible, so the recoil mechanism was pretty important, because if it wasn't designed properly, the gun would shake the hell out of the airplane and decrease accuracy.

    During night trials in the European arena of combat, the cannon muzzle flashes tended to blind pilots during operations and the aircraft had to be equipped with flash-hiders for the cannon and nose guns. This condition was especially dangerous with aircraft engaging in head-on encounters.1

    In the Pacific during World War II, M4s were salvaged from P-39s and used on PT boats.They proved very successful and a version was produced specifically for use on PT boats.

Other Armaments:
M1919 30 Cal.MG
Browning .303 Cal. MG
Browning M2 50 Cal. MG
Foster Mount
Lewis MG
Vickers MG
Mg 151/20 Cannon
M4 37 mm Cannon
Mk 108 Cannon

1. Jay Frank Dial. Aircrft in Profile, Volume 7. The Bell P-39 Airacobra.. Garden City, New York: Doubleday & Company Inc., 1970. 269.

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Created December 1,2012. Updated March 25, 2014.