Oerlikon 20

Oerlikon 20 mm cannon
A modern Oerlikon cannon (Oerlikon 20mm/85 KAA) on a Royal Navy warship
Type
Place of origin	Switzerland
Service history
In service	1940–present
Wars	World War II, various
Production history
Designer	Reinhold Becker
Designed	1939
Manufacturer	Oerlikon
Produced	1940
Variants	Oerlikon FF, MG FF cannon
Specifications
Weight	L70: Total gun barrel weight: 68.04 kilograms (150.0 lb) Minus breech mechanism: 20.865 kg (46.00 lb) L85: Empty: 92.0 kilograms (202.8 lb) Loaded with 200 rounds: 182.0 kg (401.2 lb)
Barrel length	L70: Overall: 2,210 mm (87 in) Bore: 1,400 mm (55 in) Rifling: 1,246 mm (49.1 in) L85: Overall: n/a Bore: 1,700 mm (67 in) Rifling: n/a
Shell	L70: 20×110mm RB L85: 20×128mm
Caliber	20 mm (0.787 in)
Barrels	Single barrel (progressive RH parabolic twist, 9 grooves)
Action	API blowback
Elevation	Manual training, typically able to depress to -15° and elevate to +90°
Traverse	Manual training, full 360°
Rate of fire	L70: Cyclic: 450 rounds per minute Practical: Between 250 to 320 rounds per minute L85: Cyclic: 900 to 1,000 rounds per minute
Muzzle velocity	L70: 820 m/s (2,700 ft/s) L85: 1,050 m/s (3,400 ft/s)
Effective firing range	Against low-flying aircraft (HE round) L70: 914 m (1,000 yd) L85: 1,500 m (1,600 yd)
Maximum firing range	HE round at 45° L70: 4,389 m (4,800 yd) L85: 6,800 m (7,400 yd)

L70:

L85:

L70:

L85:

L70:

L85:

L70: 820 m/s (2,700 ft/s)

Against low-flying aircraft (HE round)

HE round at 45°

The Oerlikon 20 mm cannon is a series of , based on an original German 20 mm Becker design that appeared very early in World War I. It was widely produced by Oerlikon Contraves and others, with various models employed by both Allied and Axis forces during World War II, and many versions still in use today.

During World War I, the German Reinhold Becker developed a 20 mm caliber cannon, known now as the 20 mm Becker using the Advanced Primer Ignition blowback (API blowback) method of operation. This used a 20x70 RB cartridge and had a cyclic rate of fire of 300 rpm. It was used on a limited scale as an aircraft gun on Luftstreitkräfte warplanes, and an anti-aircraft gun towards the end of that war.

Because the Treaty of Versailles banned further production of such weapons in Germany, the patents and design works were transferred in 1919 to the Swiss firm SEMAG (Seebach Maschinenbau Aktien Gesellschaft) based near Zürich. SEMAG continued development of the weapon, and in 1924 had produced the SEMAG L, a heavier weapon (43 kg) that fired more powerful 20x100RB ammunition at a slightly higher rate of fire, 350 rpm.

In 1924 SEMAG failed. The Oerlikon firm, named after the Zürich suburb where it was based, then acquired all rights to the weapon, plus the manufacturing equipment and the employees of SEMAG.

In 1927 the Oerlikon S was added to the existing product line. This fired a still larger cartridge (20x110RB) to achieve a muzzle velocity of 830 m/s (versus 490 m/s for the original Becker 20x70RB gun), at the cost of increased weight and a reduced rate of fire (280 rpm). The purpose of this development was to improve the performance of the gun as an anti-tank and anti-aircraft weapon, which required a higher muzzle velocity. An improved version known as the 1S followed in 1930.