20 mm Oerlikon

20 mm Oerlikon
Name	20 mm Oerlikon
Origin	Switzerland
Type	Autocannon
Service	1930s–present
Designer	Reinhold Becker
Manufacturer	Oerlikon Contraves
Caliber	20 mm
Action	Blowback / advanced primer ignition
Rate	450–650 rounds/min (varies)

20 mm Oerlikon

The 20 mm Oerlikon is a family of single-barrel autocannon originally designed in the 1930s in Switzerland by Reinhold Becker and produced by Oerlikon Contraves. It saw widespread adoption by the Royal Navy, United States Navy, Kriegsmarine and many other armed forces during World War II, subsequently serving in postwar navies and air arms across Europe, Asia, Africa and the Americas. Its simplicity, reliability and adaptability led to extensive use aboard destroyers, frigates, aircraft and ground vehicles in conflicts from the Spanish Civil War to the Cold War and regional wars thereafter.

History

The weapon's genesis involved Swiss engineering circles and the industrial firm Maschinenfabrik Oerlikon, linking it to Swiss neutrality debates and interwar rearmament. Early export customers included the Royal Navy, United States Navy, Imperial Japanese Navy and Kriegsmarine, which integrated the gun into fleet defense programs and coastal batteries. During World War II the cannon featured prominently in major engagements such as the Battle of the Atlantic, the Mediterranean campaigns around Malta and Tobruk, the Pacific Theater actions involving the Imperial Japanese Navy and United States Marine Corps, and in convoy defense during the Arctic convoys to the Soviet Union. Postwar reconfigurations saw continued service with navies like the Royal Canadian Navy, French Navy and Italian Navy during NATO standardization efforts and Cold War fleet modernization.

Design and Development

Design work was led by Reinhold Becker at Maschinenfabrik Oerlikon and benefited from Swiss metallurgical practices and ammunition developments influenced by firms such as Rheinmetall and Hispano-Suiza. The cannon used advanced primer ignition blowback, a concept developed earlier in European small arms research and applied to autocannons to balance weight and rate of fire. Iterations in the 1930s and 1940s involved partnerships with Royal Ordnance and US Bureau of Ordnance engineers to meet Royal Navy and US Navy requirements for anti-aircraft mounts and aircraft fittings. Development cycles reflected lessons from aerial engagements involving the Luftwaffe, Fleet Air Arm, Imperial Japanese Navy Air Service and United States Army Air Forces.

Variants and Calibres

Manufacturers and licensees produced multiple models and calibres to suit service needs, with versions chambered in 20×110mm and 20×101mm among others. Notable licensed manufacturers included Hispano-Suiza, Bofors under Swedish industrial arrangements, and entities in Italy and Japan that modified the design for local ammunition standards and mounting systems. Variants included single-barrel gun, twin mounts, and electric or manual turreted systems adopted by navies including the Royal Australian Navy, Royal Netherlands Navy, and Soviet-aligned fleets that retrofitted captured platforms during World War II and postwar periods.

Operation and Mechanism

The Oerlikon family operates on advanced primer ignition blowback, where the primer is fired while the bolt is still moving forward, permitting a lighter bolt and simpler mechanism compared with locked-breech designs used by Hispano cannon and Mauser-derived guns. Firing cycles and gas dynamics were analyzed in technical studies connected to institutions like ETH Zurich and Royal Aircraft Establishment engineers who compared recoil, muzzle velocity and rate of fire with contemporaries such as the Bofors 40 mm and M2 Browning. Maintenance doctrines were incorporated into Royal Navy and US Navy manuals, and training conducted at establishments like HMS Excellent and Naval Air Station Pensacola.

Mounts and Platforms

The gun was fitted on a wide array of mounts and platforms including single pedestal mounts on destroyers of the Royal Navy and US Navy, stabilized twin mounts on escort carriers, nose and wing installations on aircraft such as maritime patrol types, and pintle mounts for coast defense batteries. It was integrated into platforms operated by Royal Canadian Air Force, Royal New Zealand Navy, and Brazilian Navy vessels, and retrofitted to merchant ships under convoy defense programs. Shore installations and coastal batteries often supplemented ships, serving alongside radar systems developed by institutions like Bawdsey and the U.S. Naval Research Laboratory.

Combat Use and Service Record

Combat employment spanned countering dive bombers, torpedo bombers and kamikaze attacks in Pacific battles such as Leyte Gulf and Okinawa, engaging Axis aircraft over the English Channel and Mediterranean, and protecting convoys in the Atlantic against Luftwaffe and Kriegsmarine threats. Units in the British Army, United States Marine Corps, and Free French forces used vehicle-mounted and static configurations in campaigns including North Africa, Normandy and Italian campaigns. Postwar engagements included use by South African and Argentine forces in regional conflicts, and by Southeast Asian navies during Cold War skirmishes and patrol operations.

Performance and Ammunition Types

Performance metrics included muzzle velocities typically between 800 and 830 m/s depending on cartridge, effective anti-aircraft range under 2,000 meters, and cyclic rates in the 450–650 rounds per minute bracket. Ammunition types encompassed high-explosive incendiary, armor-piercing incendiary, and practice rounds compatible with cartridge designs influenced by Swiss, British and American ballistic standards. Ballistics and terminal effects were studied by ordnance departments in ministries and institutions such as the US Naval Ordnance Laboratory and Royal Armament Research and Development Establishment, informing doctrines for target engagement profiles against aircraft, light vessels and shore targets.

Reinhold Becker Maschinenfabrik Oerlikon Oerlikon Contraves Royal Navy United States Navy Kriegsmarine Imperial Japanese Navy Royal Canadian Navy French Navy Italian Navy Royal Australian Navy Royal Netherlands Navy Royal New Zealand Navy Royal Canadian Air Force United States Marine Corps Luftwaffe Fleet Air Arm Imperial Japanese Navy Air Service United States Army Air Forces Bofors Hispano-Suiza Rheinmetall ETH Zurich Royal Aircraft Establishment HMS Excellent Naval Air Station Pensacola Bawdsey U.S. Naval Research Laboratory Leyte Gulf Okinawa Battle of the Atlantic Malta Tobruk Arctic convoys Convoy PQ North Africa campaign Normandy landings Italian campaign South African Navy Argentine Navy Naval Ordnance Laboratory Royal Armament Research and Development Establishment Cold War World War II Spanish Civil War NATO United States Bureau of Ordnance Royal Ordnance M2 Browning HMS Escort carrier Destroyer Convoy Kamikaze attacks Ammunition Ballistics Armor-piercing High-explosive Incendiary Naval turret Pintle mount Coastal battery Maritime patrol aircraft Merchant navy Escort Aircraft cannon Autocannon Advanced primer ignition blowback 20×110mm 20×101mm Portugal Brazilian Navy Soviet Navy Japan United States United Kingdom

Category:Autocannon