M4 autocannon

U.S. WWII-era autocannon

The 37 mm Automatic Gun, M4, known as the T9 during development, was a 37 mm (1.46 in) recoil-operated autocannon designed by Browning Arms Company and entered service in 1942. The M4 and its variants would primarily be manufactured by Colt's Manufacturing Company and Oldsmobile and is therefore sometimes referred to as the "Colt M4" or "Oldsmobile M4." It was primarily mounted in the Bell P-39 Airacobra and P-63 Kingcobra, with the U.S. Navy also utilizing it on many PT boats.

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