Oerlikon 20mm Cannon

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US Navy Mark 4 single pedestal mount Oerlikon L70 Cannon with early-war eyepiece / ring antiaircraft sight - 20x110mm RB. This crude AA sight was replaced with the much more advanced Mark 14 Gyro Gunsight (a reflector sight with automatic target lead calculation) starting in 1943, with the improved Mark 20 replacing the Mark 14 postwar.
Twin Mark 4 Oerlikon L70 cannons in a Mark 24 mounting with Mark 14 Gyro Gunsight - 20x110mm RB. Note markings on left-handed snail drum.

The Oerlikon 20mm Cannon is a Swiss-designed 20mm API blowback operated autocannon based directly on the WW1-era Becker machine gun's descendant, the SEMAG-L. After the failure of Becker's company SEMAG in the interwar years, the Zürich-based Oerlikon company acquired all rights to the design and in 1927 began production of the Oerlikon S, the first step towards what would become the Oerlikon L70.

In 1935 the US Navy purchased two of the current model of Oerlikon for trials: they were rejected, almost bankrupting Oerlikon until they hit on the idea of designing a series of shortened Oerlikon derivatives for mounting in the wings of fighter aircraft and managed to sell production rights to, rather ironically, the Imperial Japanese Navy (which led to the development of their Type 99 cannon): the MG FF cannon was also developed from these variants. The Royal Navy rejected the same model of Oerlikon that had previously been offered to the US Navy in 1937, but stated that, if the muzzle velocity could be raised, they would be interested, and this led to the improved L70 Mark I in 1939. Only around 100 of these guns arrived in England before the annexation of France by Nazi Germany cut off the supply route, but by this point the Royal Navy had acquired the production diagrams. The British spent considerable time modifying the labor-intensive Mark I, which required extensive hand-fitting and massive forged and machined parts (such as the barrel spring housing starting out life as a 56lb solid alloy forging that had to be machined out to the final 6lb part: this was eventually replaced with a 14lb hollow forged base with a steel tube welded to it), coming up with their domestic Mark II gun in 1940, with six of the new guns being used on the battleship HMS Duke of York.

The US Navy, looking to replace obsolete AA armament consisting mostly of unreliable 1.1"/75 caliber gun quadmounts and .50 caliber water-cooled Browning M2s with insufficient range or power to shoot down period aircraft, became interested in the British work and designed their own Mark 2 gun in 1941. Over the course of the war the gun was repeatedly reworked to maximize production speed, cutting the 428.4 man-hours per gun in 1941 down to 76.2 hours by September 1944. In 1943 the USN began to equip their Oerlikons with the cutting-edge electromechanical Mark 14 Gyro Gunsight, making them even more effective (the same device was also used on standalone pedestal mounts to direct 1.1"/75 caliber and 40mm guns: in this application it was called the Gun Director, Mark 51). The various Oerlikon variants (mostly the Mark 4 gun, which eliminated the barrel cooling ribs of earlier American variants, was built to Imperial rather the metric standard measurements, and featured only a single heavy buffer spring) proved extremely effective in the Pacific War with 32% of all Japanese aircraft shot down between December 1941 and September 1944 being taken down by Oerlikon guns, and was the primary AA gun on American warships until the Bofors 40mm became available in large numbers in 1943, only beginning to lose effectiveness with the rise in Japanese use of Kamikaze attacks which led to a strong preference for the 40mm Bofors in 1944-45.

By the end of the war the British had manufactured some 55,000 guns while the United States had built a total of 124,735. The Oerilikon was also used by the German Kriegsmarine as the FlaK 28 and FlaK 29. Oerlikons were typically pedestal mounted on warships, either as single or dual mounts which were often manually aimed but sometimes power-assisted. Left-handed guns required special left-handed snail drums, which featured distinctive markings to prevent loading mistakes. Experiments were made with other mounts including a British attempt at designing a belt-fed variant, the uncommon USN Mark 15 quadmount and a USN triple mount which never left the prototype phase due to problems loading the middle gun. Following the war it was a common sight on smaller ships such as PT boats, and is still mounted on some warships today, with British auxiliary ships carrying Oerlikons as late as 2006. When the USN liquidated their vast stockpiles of surplus Oerlikons in the 1950s, most were scrapped or sent overseas but a few ended up on the civilian marked as transferable NFA weapons, and some of these authentic fully-automatic weapons do exist in the hands of movie armorers.

The other gun known as the Oerlikon 20mm is the 20mm Oerlikon KAA, also known as the Oerlikon L85. This gun was developed in the 1950s but not really common until after the Falklands War renewed interest in light warship armament. This page, however, is for the L70 version.

Contents

Specifications

Oerlikon L70

(1939-present (US production 1940-1945))

  • Caliber: 20x110mm RB
  • Weight: 1,695 lbs (768.8 kg) (complete USN Mark 2 or 4 single mount), 150 lbs (68 kg) (gun only)
  • Length: 87 in (221 cm)
  • Barrel Length: 55.1 in (140 cm)
  • Capacity: 60 round snail drum, 100-round version also available postwar
  • Fire modes: Mark I semi / auto, all other variants auto-only, cyclic 450 rounds per minute, practical 250-320 rounds per minute
  • Effective range: 1,000 yards (914m) against aircraft with HE-I Mark 3 shell, USN Oerlikon gunners typically opened fire at 1,200-1,300 yards (1,097-1,189m) for aiming correction (absolute maximum range 4,800 yards (4,389m) elevated at 45 degrees: AA ceiling 10,000 feet (3,048m))

The Oerlikon 20mm Cannon and variants can be seen in the following films, television series, video games, and anime used by the following actors:

Film

Title Actor Character Note Date
The Fighting Seabees US Marine 1944
Hong Kong on coast guard cutter 1952
The Beast from 20,000 Fathoms US National Guards 1953
Above Us the Waves Mounted on German patrol boat 1955
Blue Arrow (Golubaya strela) Mounted on a submarine 1958
The Guns of Navarone Mounted on German patrol boat 1961
Gorgo Mounted on US Navy submarine 1961
The Longest Day German soldiers 1962
Diamonds Are Forever SPECTRE operatives Mounted on oil rig 1971
Murphy's War German sailors Mounted on the unnamed German U-boat 1971
Thunderbolt and Lightfoot Clint Eastwood Thunderbolt 1974
Midway Mounted on US Navy ships 1976
The Eagle Has Landed Mounted on a German boat 1976
Soldier of Orange Mounted on Royal Navy fast boat; German coastal defence 1977
Uncommon Valor 1983
Rambo III Richard Crenna Colonel Trautman Acetylene Gas Mockup 1988
Return from the River Kwai Mounted on US Navy submarine 1989
The Manchurian Variant (Manchzhurskiy variant) seen in documentary footage of Pacific War 1989
Mediterraneo Mounted on Italian Royal Navy ship on twin mounting, with Mark 14 Gyro Gunsight 1991
Hot Shots! Part Deux The Iraqi Navy Officer Custom version 1993
The Postman The Holnists 1997
The Thin Red Line Mounted on US Navy ship on twin mounting 1998
U-571 Mounted on US Navy submarine 2000
Pearl Harbor Mounted on USS Texas 2001
Below mounted on the deck of the USS Tiger Shark 2002
Stealth Defenders of mountain fortress 2005
Flags of Our Fathers Mounted on US Navy ship 2006
The Curious Case of Benjamin Button Mounted on German U-boat 2008
X-Men: First Class Mounted on US Navy ship on twin mounting 2011
Emperor 2013
Dunkirk mounted on the British Motor Torpedo Boat and the Destroyer Maillé-Brézé 2017

Television

Show Title Actor Character Note / Episode Air Date
Airwolf Libawe soldiers "And They Are Us" (S1E09) 1984

Video Game

Game Title Appears as Mods Notation Release Date
Medal of Honor: Frontline Kriegsmarine FlaK 29 on the loading screen for Level 1 of The Hornets Nest (Mission 6) 2002
Call of Duty: World at War Mounted on PBY Catalina 2008
Grand Theft Auto V mounted on Half-Track 2013
Call of Duty: WWII 2017

Anime

Title Character Note Date
Rebuild of Evangelion Misato's Iowa-class battleships 2007-2012

Animation

Title Character Note Date
Archer German Sniper "Heart of Archness, Part I" (S03E01). 2011-2012



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