During World War I, German engineer Reinhold Becker developed one of the earliest 20mm automatic cannons, later known as the 20mm Becker. Originally mounted on Luftstreitkräfte aircraft and used in limited numbers as an anti-aircraft gun near the end of the war, it represented a major step forward in automatic cannon design.
After Germany’s defeat, the Treaty of Versailles prohibited further development or production of such weapons. To preserve the design, Becker’s patents and tooling were transferred in 1919 to the Swiss firm SEMAG near Zürich, which continued improving the design. When SEMAG went bankrupt in 1924, the nearby Oerlikon Werkzeugmaschinenfabrik acquired all rights, equipment, and engineering data—giving rise to the famous Oerlikon 20mm cannon.
By the start of World War II, the Oerlikon had become a proven design adopted by numerous Allied nations. The U.S. Navy possessed only a few hundred examples when Japan attacked Pearl Harbor on December 7, 1941, but quickly ramped up production. Unlike many foreign models that used belt feeds, the American variant featured a distinctive 60-round spring-driven drum magazine mounted on top of the gun. Through widespread licensing and contracts with automobile manufacturers like Hudson and General Motors, more than 120,000 units were produced before the war’s end.
When paired with the MIT-developed Mark 14 electric gunsight—a gyro-stabilized device that automatically computed lead on fast-moving aircraft—the Oerlikon became one of the most advanced and effective naval anti-aircraft systems of the era.
Mounted on everything from patrol craft and minesweepers to destroyers and aircraft carriers, the rugged Oerlikon 20mm was usually manned by a five-man crew, though it could be operated by a single sailor in emergencies. Post-war analyses revealed its extraordinary impact: nearly one-third of all Japanese aircraft shot down over the Pacific fell to the German-designed, Swiss-refined, and American-built Oerlikon 20mm cannon.
