Oerlikon 20mm Cannon

The Oerlikon 20mm cannons are a series of Swiss-designed 20mm API blowback operated autocannons 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 the mid-1920s began production of the Oerlikon F, Oerlikon L, and Oerlikon S; these three were the same basic design, progressively scaled up in longer 20mm cartridges.
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 derivatives for mounting in the wings of fighter aircraft, these being the FF F, FF L, and FF S. In an ironic (with hindsight) twist, the company was saved when the Imperial Japanese Navy bought production rights to the FF F and FF L, developing them into the Type 99 Mark 1 and Type 99 Mark 2, respectively; the Germans also developed the FF F into the MG FF.
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. After this, Oerlikon developed a new iteration of the original cannon making use of the improvements from the FF series, resulting in the SS in 1938. The Oerlikon SS would be the design adopted and used extensively by the Americans and British during WWII. The British adopted the SS as the Mark I in 1939, but 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, coming up with their domestic Mark II gun in 1941.
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 Oerlikon 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 L/85. 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 L/70 version.
==Specifications==
Oerlikon SS
(1939-present (US production 1940-1945))
* Caliber: 20x110mm RB
* Weight: 1,695 lbs (768.8 kg) (complete USN Mark 2 or 4 single mount), (gun only)
* Length: 
* Barrel Length: 
* Capacity: 60 round snail drum, 100-round version also available postwar
* Fire modes: original SS featured semi or auto, US/British 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))
=== 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
Soldier of Fortune 	Clark Gable 	Hank Lee 	Mounted on Lee's junk 	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
Concorde Affaire '79 	 	 	Single mount on French patrol boat P659 Canopus 	1979
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
Captain Corelli's Mandolin 	German soldiers	 	Mounted on German landing crafts' 	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
Hunting the Phantom 	 	 	Mounted on the ship 	2014
Dunkirk 	 	 	Mounted on the British Motor Torpedo Boat and the Destroyer Maillé-Brézé 	2017
Godzilla Minus One 	 	 	Mounted on a US Navy Liberty ship 	2023
=== Television ===
Show Title 	Actor	Character 	Note / Episode 	Date
Airwolf 	 	Libawe soldiers 	"And They Are Us" (S1E09) 	1984
Loki - Season 1	 	USS Eldridge sailors	Mounted on USS Eldridge; "Journey Into Mystery" (S1E05)	2021
===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
Medal of Honor: European Assault	 	 	Mounted on the HMS Campbeltown 	2005
Call of Duty: World at War 	 	 	Mounted on PBY Catalina 	2008
Company of Heroes 2 	 	 	Twin-mounted on Centaur AA Mk. II Cruiser Tank 	2013
Grand Theft Auto V 	 	 	mounted on Half-Track 	2013
Rainbow Six Siege 	 	 	Unusable; seen on photo 	2015
Call of Duty: WWII 	 	 	 	2017
Battlefield V 	 	 	Mounted in Valentine AA tank 	2018
Call of Duty: Vanguard 	 	 	Unusable; mounted on aircraft carrier 	2021
Enlisted 	 	 	Oerlikon Mark 4 	2021
Enlisted 	 	 	20 mm Polsten 	2021
===Anime===
Title 	Character 	Note 	Date
The Cockpit 	U.S. Navy sailors	Ep. 2 "Sonic Boom Squadron"; mounted on American aircraftcarrier	1993
Rebuild of Evangelion 	 	Misato's Iowa-class battleships 	2007-2012
Strike Witches 2 	 	Single mounts on Fletcher-class destroyers 	2010
Strike Witches: Operation Victory Arrow	 	Single mounts on Liberty ships 	2014-2015
Brave Witches 	 	Single mounts on Liberty ships 	2016-2017
Strike Witches: Road to Berlin 	 	Single mounts on Liberty ships 	2020
Luminous Witches 	 	Single mounts on Sangamon-class carrier 	2022
===Animation===
Title 	Character 	Note 	Date
Archer	German Sniper	"Heart of Archness, Part I" (S03E01).	2011-2012
Category:Gun
Category:Cannon