The Oerlikon autocannon is a type of rapid-firing, air-cooled 20x110mmRB automatic cannon designed for anti-aircraft and anti-surface warfare. It was developed by the Swiss company Oerlikon Contraves during the early 20th century and became widely used by various armed forces around the world. The Oerlikon autocannon is known for its reliability, effectiveness, and adaptability to different platforms, including naval vessels, aircraft, and ground-based anti-aircraft mounts. It can feed from drums of 30, 45, 60, 75 or 100 rounds, but the 60 round drum is by far the most common. During World War II, this weapon found extensive use on naval ships of various countries for defence against enemy aircraft and surface targets. It provided a balance between firepower, weight, and size, making it suitable for mounting on warships without compromising their overall capabilities. Even in the mid-1960s it remains an obvious choice for any warship, from a German dreadnought to the most ramshackle pirate motorboat.
Many variants were produced of the Oerlikon. The FF Series in particular, however, proved extremely popular as aircraft armament and spawned a wide variety of aerial cannon and anti-aircraft guns, including the MG FF and Hispano-Suiza HS.404.