The 20 mm Oerlikon cannon is an automatic cannon produced by Oerlikon Contraves, based on a weapon designed by the German Reinhold Becker at the start of the First World War. Many variants of this gun were used during World War II, and some are still in service as of 2014.
History
Origins
During World War I, German Reinhold Becker developed a 20 mm cannon, the 20 mm Becker gun using the APIn 1 blowback. It used 20 × 70 mm ammunition and had a rate of fire of 300 strokes per minute. It was mainly used mounted on aircraft and as an anti-aircraft gun towards the end of the war.
Because of the Treaty of Versailles, which banned the production of such weapons in Germany, the patents and designs were transferred in 1919 to the Swiss firm SEMAG (Seebach Maschinenbau Aktien Gesellschaft), based near Zurich. SEMAG improved the weapon and in 1924 it put into production the SEMAG L, a heavy weapon (43 kg) which fired more powerful ammunition (20 × 100 mm) at a slightly higher rate of 350 rounds per minute.
That same year, SEMAG went bankrupt. The firm Oerlikon (named after the suburb of Zurich where it is based) then acquires the rights to the weapon, as well as the factories and employees of SEMAG.
Oerlikon
In 1927, the Oerlikon S was added to the production line. It fires even larger ammunition (20 × 110 mm) and reaches a muzzle velocity of 830 m/s (compared to 490 m/s for Becker's original gun). On the other hand, the rate of fire is reduced (280 rounds per minute). The purpose of this version is to improve the gun's performance as an anti-tank and anti-aircraft weapon, which requires a higher muzzle velocity.
World War II
The 20 mm Oerlikon cannon was particularly used in navies. Initially, the Royal Navy did not favor this gun for close air defence. During the years 1937-1938, Lord Louis Mountbatten, then a captain in the Royal Navy, tried to convince the high command to assess the capabilities of this gun, in vain. The situation changed when Admiral Roger Backhouse, then Commander-in-Chief of the Home Fleet, was appointed First Sea Lord.
During the first half of 1939, a contract for 1,500 guns produced in Switzerland was concluded. However, due to delays and then the fall of France in June 1940 only 109 guns were delivered to the UK. All Oerlikon guns imported from Switzerland in 1940 were mounted on different carriages to serve as ground anti-aircraft guns. A few weeks before the fall of France, Oerlikon approved the manufacture of these guns in the United Kingdom under licence. The Royal Navy managed to smuggle the necessary plans and documents out of Zürich. Production of the first British Oerlikon guns began in Ruislip, a London suburb at the end of 1940. The first guns were delivered to the Royal Navy in March or April 1941.
The 20 mm Oerlikon guns designed by Oerlikon were one of the most produced anti-aircraft weapons during the Second World War. The United States alone produced 124,735. When introduced in 1941, this gun replaced the 12.7mm M2 machine guns and remained the primary anti-aircraft weapon until the introduction of the 40mm Bofors gun in 1943.
Between December 1941 and September 1944, 32% of Japanese aircraft shot down were attributed to this weapon with a maximum of 48.3% in the second half of 1942. In 1943, the new Mark 14 sighting system considerably improved the effectiveness of these guns. However, they proved ineffective against kamikaze attacks late in the war and were replaced by 40mm guns.
Service features
Type Autocannon
Service 1940 -
Production
Designer Switzerland
Year of design n 1924
Manufacturer Oerlikon
Production 1927
General characteristics
Barrel length only L70:2.21 m
Caliber 20mm
Rate of fire L70:450 strokes per minute L85:900 strokes per minute
Initial velocity L70:820 m/s L85:1,050 m/s
Practical range L70:914 m L85:1,500 m
Maximum range L70:4,389 m L85:6,800 m
Ammunition 20mm shell