The 40mm Bofors was a Swedish anti-aircraft gun used by the US and British navies during World War II. It was also deployed by ground forces during the same armed conflict, as well as the Korean and Vietnam Wars. Designed and manufactured by Bofors Defence, it was the most successful AA gun of World War II and it is still used today by navies and armies around the world. It became well-known for being used against approaching Japanese kamikaze aircraft in single, twin, and quadruple mountings on the decks of every US warship. It entered service with the Swedish Navy in 1934, but was soon acquired by other nations, such as Poland, the United Kingdom, and the United States, where it was massively produced with improvements in the gun sights and mountings.
With a maximum ceiling of 7,200 m, the 40mm Bofors was an automatic gun that fired 40x364mmR ammunition, which was a powerful shell that could shoot down and even rip to pieces any fast-flying single-engine aircraft. The US naval version was fed from 4-round clips. It had a muzzle velocity of 860 m/s and a cyclic rate of fire of 120 rounds per minute as its air-cooled barrel could be quickly replaced. Like the German anti-aircraft guns, it had a 360º traverse and an elevation of -5º to +90º. The US Army version was usually mounted on a 4-wheeled carriage, but was also emplaced on the M24 Chaffee chassis.