Early in World War II U.S. forces were equipped with the M1 37mm Anti-Aircraft Gun for light anti-aircraft duty. The M1 was adopted in 1938 and had variants M1A1 and M1A2. It was superceded by the Bofors 40mm Anti-Aircraft Artillery as that weapon became available, with most of the 37mm anti-aircraft guns replaced by early 1943.
The light and mobile M1 37mm Anti-Aircraft Gun was mounted on a four-wheel carriage operated by a crew of seven, one of several mounts used. The platform allowed the gun to traverse a full 360° -- folding outriggers gave stability to the gun when emplaced. The ammunition was fed in a ten round clip for a sustained rate of fire of 90 rounds per minute. It could reach a ceiling of 18,500 feet with high explosive rounds, guided by the M5 Director system.
The Technical Manual is TM 9-235.
M1 37mm Anti-Aircraft Artillery.
37mm Anti-Aircraft Gun in production at a Pennsylvania factory, December 1941.
African-American U.S. Army Engineer unit on a transport to Liberia, Africa, conducting live fire training with 37mm Anti-Aircraft Artillery, early World War II.