The Royal Small Arms Factory ADEN cannon (ADEN being an acronym for "Armament Development, Enfield") is a 30 mm revolver cannon used on many military aircraft, particularly those of the British Royal Air Force and Fleet Air Arm. Developed post-World War II primarily to meet British Air Ministry's requirement for increased lethality in aircraft armament, the cannon was fired electrically and is fully automatic once it is loaded. Design and development During World War II, the German firm Mauser began development of a radically new 20 mm autocannon using a motorised firing mechanism in order to improve the rate of fire. The weapon got the preliminary designation Mauser MG 213 and by the late-war period the design was beginning to mature. However the presence of large heavy bombers like the Boeing B-17 Flying Fortress and Avro Lancaster led to the need of up-arming Luftwaffe fighter aircraft with heavier cannons. Mauser responded to this by adapting the MaschinenGewehr 213 to fire the 30 mm rounds from the MK 108 cannon. This variant got the preliminary designation Maschinenkanone 213, as the 30 mm caliber meant that the weapon was classed as a cannon in German nomenclature. The 30 mm rounds on the MK 108 cannon had a fairly short cartridge with limited propellant capacity (30×90mm), and thus had a low muzzle velocity of around . However, as they were adapted with mine shells, which could effectively knock out any aircraft at the time with just a few hits, they did not need high velocity to be effective against non-manoeuvering targets like bombers. Despite frantic efforts, production of the MK 213 never commenced due to development problems such as excessive barrel wear, not to mention the Allied Combined Bomber Offensive campaign against German industry. At the end of the war only 5 prototypes (V1 to V5) of either 20 mm MG 213 or 30 mm MK 213 were finished. In the post-war era, the MK 213 became well known in armament circles, and a number of companies took up development. This included the Armament Development Establishment in the UK and GIAT in France. A common 30×111mm round was developed that offered a dramatic improvement in muzzle velocity from the MK 108's 540 m/s to the new design's . This was only slightly lower than contemporary 20 mm cannon like the Hispano Mk. V's , making the new round suitable for use during dogfights