Oerlikon 20 mm cannon

Oerlikon 20 mm cannon
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Name	Oerlikon 20 mm cannon
Type	Autocannon
Origin	Switzerland
Designer	Reinhold Becker
Manufacturer	Oerlikon Contraves, Rheinmetall, Hispano-Suiza
Calibertype	20×110mm / 20×128mm
Action	Blowback / Advanced primer ignition
Rate	450–650 rpm
Feed	Drum magazine / Belt
Length	2.1 m (varies)
Weight	35–80 kg (varies)

Oerlikon 20 mm cannon The Oerlikon 20 mm cannon is a family of Swiss-designed autocannons originating in the interwar period, widely adopted for naval, anti-aircraft, and aircraft armament during World War II and the Cold War. Developed from Becker designs, the weapon influenced air defense on warships and ground installations across Europe, North America, and Asia, becoming a standard close-in weapon system before being largely superseded by modern rotary and guided systems.

Design and development

The lineage begins with designer Reinhold Becker and the company Maschinenfabrik Oerlikon, whose development paralleled contemporaries such as the Luftwaffe procurement efforts and the Royal Navy's anti-aircraft requirements. The cannon uses advanced primer ignition blowback operation, a principle also examined by designers at Rheinmetall and Hispano-Suiza, enabling a relatively simple mechanism compared with gas-operated designs fielded by the United States Navy and Soviet Navy. Early trials attracted interest from the Kriegsmarine, Royal Air Force procurement officers, and the Imperial Japanese Navy, prompting adaptations for shipboard and aircraft installations similar to how the Bofors 40 mm and Browning M2 influenced service armaments. Naval architects from the Royal Navy and the United States Navy evaluated mounting concepts that balanced rate of fire, elevation, and traverse for escorts involved in convoy escorts during the Battle of the Atlantic and Pacific Theater engagements.

Variants and models

Multiple models evolved to meet requirements from the Kriegsmarine, Royal Canadian Navy, and Imperial Japanese Navy, including versions with drum magazines, twin mounts, and electrically driven powered mounts comparable in tactical niche to the twin 40 mm Bofors and single 37 mm flak guns. Notable lines include the early 20×70R and subsequent 20×110mm and 20×128mm chamberings, paralleling developments by Hispano-Suiza and Rheinmetall for fighter armament used by units of the Luftwaffe, Fleet Air Arm, and United States Army Air Forces. Twin and quad mountings were integrated aboard destroyers, corvettes, and aircraft carriers, and configurations were adapted for land use by armies such as the Wehrmacht, British Army, and United States Marine Corps for airfield defense during campaigns like the North African Campaign and the Normandy landings.

Ammunition and ballistics

Ammunition types include high-explosive, high-explosive incendiary, armor-piercing, and tracer rounds, with ballistic performance influenced by cartridge length (20×110mm vs 20×128mm) and propellant choices explored by ordnance bureaus in Washington, D.C., London, and Berlin. Muzzle velocity and terminal effects compare with other contemporary autocannons such as the Hispano-Suiza HS.404 and the Soviet ShVAK, with trade-offs between projectile mass, muzzle velocity, and rate of fire that informed doctrine at establishments like the Naval Ordnance Laboratory and the Royal Armaments Research and Development Establishment. Ballistic tables produced for the Admiralty and the United States Navy were used to set fire-control solutions alongside optical predictors and early radar sets developed by teams at Bawdsey and the Massachusetts Institute of Technology.

Operational history

The cannon saw extensive service in World War II with navies and air arms engaged in the Atlantic, Mediterranean, and Pacific theaters; ship classes ranging from escort carriers to corvettes deployed the weapon in anti-aircraft and surface-action roles during operations such as the Arctic convoys and the Guadalcanal campaign. Postwar, NATO navies including the Royal Navy, Royal Canadian Navy, and Bundesmarine retained Oerlikon mounts during the Korean War and early Cold War crises until systems like the Phalanx CIWS and Goalkeeper began replacing them during later modernization driven by lessons from the Falklands War and missile-era threat assessments by defense ministries in Paris, Washington, and London. Ground and naval crews from the British Commonwealth, Imperial Japanese forces, and the United States Marine Corps credited the weapon for point-defense successes during amphibious operations and convoy protection missions.

Manufacturing and licensing

Production and licensing agreements proliferated: licensed manufacture occurred in Germany by Rheinmetall, in France by Hispano-Suiza, in the United Kingdom under subcontractors supplying the Royal Navy, and in the United States under wartime procurement contracts with manufacturers supporting the War Production Board. International licensing spread to companies serving the Royal Canadian Navy, the Royal Australian Navy, and Asian firms supplying the Imperial Japanese Navy earlier in the conflict, reflecting export policies and intergovernmental procurement arrangements similar to Lend-Lease-era transfers and bilateral industrial cooperation seen between the United States and allies.

Survivability and replacements

By the late 20th century, the Oerlikon 20 mm family was increasingly viewed as vulnerable to supersonic anti-ship missiles and high-speed attack aircraft, leading admiralties and defense departments to favor radar-directed CIWS like the Phalanx and electrically stabilized systems such as Goalkeeper, as well as medium-caliber automatic cannons in the 30–76 mm range produced by companies including OTO Melara and BAE Systems. Nevertheless, preserved examples remain in naval museums, private collections, and as secondary armament on vintage vessels maintained by heritage organizations and maritime museums, illustrating the cannon's historical role alongside the evolution of naval and air defense doctrine.

Reinhold Becker Maschinenfabrik Oerlikon Rheinmetall Hispano-Suiza Kriegsmarine Royal Navy United States Navy Royal Canadian Navy Imperial Japanese Navy Luftwaffe Fleet Air Arm United States Army Air Forces Bofors 40 mm Browning M2 Wehrmacht British Army United States Marine Corps North African Campaign Normandy landings Massachusetts Institute of Technology Bawdsey Naval Ordnance Laboratory Royal Armaments Research and Development Establishment Atlantic (Theatre of World War II) Mediterranean Sea Pacific Theater of Operations Arctic convoys Guadalcanal campaign Korean War Cold War Falklands War Phalanx CIWS Goalkeeper OTO Melara BAE Systems War Production Board Lend-Lease Royal Australian Navy United States France Germany United Kingdom Canada Japan Italy Massachusetts London Paris Washington, D.C. Admiralty Naval architects Optical fire-control Radar Drum magazine Twin gun mount Quad mount Armor-piercing High-explosive incendiary Tracer round Muzzle velocity Rate of fire 20×110mm 20×128mm Hispano-Suiza HS.404 ShVAK Shipborne anti-aircraft artillery Close-in weapon system Maritime museum Heritage organization Convoy Amphibious warfare Airfield defense Ordnance bureau Subcontractor Export policy Industrial cooperation Procurement Manufacturing license Automatic cannon Autocannon Anti-aircraft gun Naval warfare Air defense Ammunition Ballistics Survivability Replacement systems Historical preservation Museum ship