M-1939 (61-K) Russian 37mm Towed Anti-Aircraft Gun

The 37 mm automatic air defense gun M1939 (61-K) (Russian: 37-мм автоматическая зенитная пушка образца 1939 года (61-К)) is a Soviet 37 mm caliber anti-aircraft gun developed during the late 1930s and used during World War II. The land-based version was replaced in Soviet service by the ZSU-57-2 during the 1950s. Guns of this type were successfully used throughout the Eastern Front against dive bombers and other low- and medium-altitude targets. It also had some usefulness against lightly armored ground targets. Crews of the 37 mm AD guns shot down 14,657 Axis planes. The mean quantity of 37 mm ammunition to shoot down one enemy plane was 905 rounds. The Soviet Navy purchased a number of Bofors 25 mm Model 1933 guns in 1935, trials of the weapon were successful and it was decided to develop a 45 mm version of the weapon designated the 49-K. The development under the guidance of leading Soviet designers M. N. Loginov, I. A. Lyamin, and L. V. Lyuliev were successful, but the army thought that the 45 mm caliber was a little too large for an automatic field weapon. In January 1938 the Artillery Factory Number 8 in Sverdlovsk was ordered to develop a 37 mm weapon based on the same design. The task was fulfilled by the chief designer of the factory, Mikhail Loginov, and his assistant Lev Loktev. Firing trials of the new 61-K were conducted in October 1938. Competitive firing trials were conducted in 1940 between the 61-K and the Bofors 40 mm/56. There were no substantial differences found between them. The weapon was initially installed as a single-barrel weapon on a four-wheeled ZU-7 carriage and was soon ready for service. An initial order for 900 units was placed. The gun was operated by a crew of eight men. A total of 200 rounds of ammunition were carried which were fed into the gun in five-round clips. Total Soviet production was around 20,000 units, ending in 1945. However, it has also been produced in Poland, China, and North Korea. Armor penetration of the armor-piercing (AP) rounds is reported as 37 millimeters of rolled homogeneous armor (RHA) at 60°at 500 meters range and 28 millimeters of RHA at 90° at 1,500 meters range.