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The Hispano Suiza 20 mm cannon was one of the most widely used aircraft weapons of the 20th century, used by British, American, French, and many other military services.
Development
This cannon was based on the earlier Swiss Oerlikon HS.7/HS.9 weapons, which Hispano Suiza manufactured under license. In the late 1930s engineer Mark Birkgit designed a new and much improved version with a revised action, faster rate of fire, and higher muzzle velocity. This entered service as the HS Type 404. This was adopted by the RAF and FAA in 1941 as the Hispano Mk II and by the U.S. as the M1 and incrementally improved M2 (although American-made weapons had minor production differences that made them notably less reliable than their British counterparts). It was primarily used by the U.S. Navy. The British upgraded to the Mk V, which was lighter and had a higher rate of fire, and the U.S. followed suit with the M3. After World War II the USAF adopted a version of the M3 cannon as the M24, similar in most respects except for the use of electrically primed ammunition.
The Hispano fired a 130 gram (4.59 oz) 20 mm x 110 mm projectile with a muzzle velocity between 840 and 880 m/s (2,755 and 2,888 ft/s), depending on barrel length. Rate of fire was between 600 and 850 rounds per minute. It was 2.36 m (7 ft 9 in) long, weighing between 42 and 50 kg (93 and 110 lb). The British Mk V and American M3/M24 weapons were lighter with higher rates of fire than the early HS 404 guns.
The U.S. Navy later replaced the M3 with the Colt Mk 12 cannon, while the British RAF and FAA went to the 30 mm ADEN cannon. The USAF adopted the M39 revolver cannon to replace the M24.
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