Oerlikon 20 mm cannon

Oerlikon 20 mm cannon is a family of autocannons of Swiss origin that became one of the most widely used anti-aircraft and light naval artillery weapons of the 20th century. Developed by the firm Oerlikon Contraves, its design traces its lineage to the Becker Type M2 cannon of World War I. The weapon's simplicity, reliability, and effectiveness against low-flying aircraft secured its adoption by numerous Allied and Axis powers navies and armies during World War II.

Development and history

The cannon's development began with the work of Reinhold Becker in Imperial Germany, whose Becker Type M2 was used on Zeppelin airships. After the Treaty of Versailles prohibited German development, the design was acquired by the Swiss firm Semag, which later became part of Oerlikon Contraves. Under the leadership of Anton Gazda, the company refined the mechanism into the Oerlikon F and FF models in the 1930s. Initial sales were slow until the Imperial Japanese Navy purchased a license, producing it as the Type 99 cannon. The British Admiralty, recognizing the Royal Navy's deficiency in close-range air defense after the Battle of Britain, began mass production in 1940, with Vickers-Armstrongs and the Admiralty Research Establishment playing key roles.

Design and variants

The core design uses an advanced primer ignition blowback operation, a simple mechanism with few moving parts, making it robust and easy to maintain. Early variants like the Oerlikon F fired the 20×72mmRB cartridge, but the definitive World War II version, the Oerlikon FF, used the more powerful 20×110mmRB round. The primary Allied variant was the **Mk I** through **Mk V**, manufactured in the United Kingdom, United States, and Canada. The United States Navy designated its version the **20 mm Oerlikon Mk 4**, producing over 124,000 units. Axis variants included the German **20 mm Flak 28** and **20 mm Flak 29**, and the Japanese Type 99 cannon. Post-war developments led to the **Hispano-Suiza HS.804** and modern Oerlikon KAA and Oerlikon KAB models used on vehicles like the Marder.

Operational use

The cannon saw extensive service as a light anti-aircraft gun on virtually every major class of Allied warship, from aircraft carriers like HMS ''Illustrious'' to destroyers and landing craft. It was pivotal in defending against kamikaze attacks in the Pacific War and Atlantic convoys. The Royal Air Force used it on aircraft like the Westland Whirlwind, while the German Wehrmacht deployed it for air defense in the Battle of France and North African campaign. Post-war, it served in conflicts including the Korean War on ships like HMCS ''Haida'', the Suez Crisis, and the Falklands War aboard HMS ''Hermes''.

Ammunition

The standard round is the 20×110mmRB (rimmed belt), a centrefire cartridge with a rebated rim. Common types included **High Explosive (HE)**, **High Explosive Incendiary (HEI)**, and **Armor-Piercing (AP)**. The HE shells, such as the British **Mk II**, used a base fuze with a self-destruct mechanism. The United States Navy developed the **Mk 100** series projectiles. Ammunition was typically fed from a 60-round drum magazine, though some aircraft installations used belt feeds. The cartridge's performance was superior to the .50 BMG round used in the M2 Browning but was later supplanted by more powerful rounds like the 20×128mm used in the Oerlikon KAD.

Users

A vast array of nations employed the cannon. Major World War II users included the United Kingdom, United States, Soviet Union, Nazi Germany, Empire of Japan, and Italy. It was license-produced in nations such as Japan (Kure Naval Arsenal), the United Kingdom (British Admiralty), and the United States. Post-war, it was widely exported, seeing service with France during the First Indochina War, Israel in the Six-Day War, and Argentina during the Falklands War. Many remain in reserve or ceremonial use with navies worldwide, including India and Pakistan.

Category:Autocannon Category:World War II anti-aircraft guns Category:Naval weapons of Switzerland