20 mm Oerlikon Anti-Aircraft Gun
|Country of Origin||Switzerland|
|Barrel Length||1,246 mm|
|Rate of Fire||450 rounds/min|
|Muzzle Velocity||820 m/s|
Contributor: C. Peter ChenDuring WW1, Reinhold Becker designed a 20-mm autocannon that saw limited use. In 1919, the firm Seebach Machinenbau Aktien Gesellschaft of Switzerland purchased the design, and the company was in turn bought out by another Swiss company, Werkzeug Maschinenfabrik Oerlikon. During the inter-war years, a series of 20-mm Oerlikon autocannons were built, including the FF, FFL, S, and SS variants.
The 20-mm Oerlikon autocannons were single-barreled weapons operated by blowback. Ammunition was fed through the top, and empty cartridges were ejected from below. The triggers were located on the right handle. The aiming mechanisms were often the simple ring-and-bead sights.
The 20-mm Oerlikon autocannons were used by both sides of WW2. During the inter-war years, Japan produced the FF and FFL variants as the Type 99 Model 1 and Model 2 autocannons used by the Japanese Navy, both shipboard as well as with aircraft; for example, the A6M Zero fighters built by Mitsubishi were equipped with them. Meanwhile, Germans built the MG FF and MG FFM autocannons, also based on the FF variant; the famed German Bf 109 fighters were equipped with MG FF autocannons.
The Royal Navy adopted Oerlikon autocannons much later compared to the Germans and the Japanese, not signing a contract with the Swiss firm until 1939. The contract was for 1,500 units, but only 109 units were delivered due to the German invasion of France. However, sensing German threat, Oerlikon approached the British government and asked for permission to relocate its production to the United Kingdom, which was granted immediately. The Royal assisted the company in sneaking technical drawings and other documents out of Zürich, and by end of 1940 British-made 20-mm Oerlikon autocannons were coming off the production line of the new factory at Ruislip, London, England. The first delivery of these British-built Oerlikon autocannons were made to the Royal Navy in Mar or Apr 1941.
Starting in 1942, 20-mm Oerlikon autocannons were being used by the United States Navy as well, replacing the M2 Browning machine gun as the standard short-range anti-aircraft weapon. Although they lacked stopping power against heavy aircraft, they nevertheless played a critical role in the Pacific War, particularly against special attack kamikaze aircraft that often got close to American ships.
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