The 37 mm Automatic Air Defense Gun M1939 (61-K) was a Soviet anti-aircraft gun used extensively during World War II and proved very successful against targets like German dive-bombers and low flying aircraft.
Designed in 1939, it was based on the Swedish Bofors 40 mm but adapted for Soviet production. It had a 37 mm caliber, a rate of fire of 160 rounds per minute, and an effective range of 4,000 meters (13,120 feet) against aircraft. Using a clip-fed autoloading system, it could fire high-explosive and armor-piercing rounds, making it effective against both aircraft and light ground targets. The 61-K 37 mm fragmentation shell weighed 730 grams, 770 grams for the armor piercing version. Weighing 2,100 kg (4,630 lbs) in combat, it was towed by trucks for mobility.
With over 20,000 units produced, the 61-K was widely used by Soviet forces and remained in service long after the war, influencing many post-war anti-aircraft designs.
