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A quad 30 mm ADEN cannon package from the pictured Hawker Hunter.

The Royal Small Arms Factory ADEN is a 30 mm cannon used on many military aircraft, particularly those of the British RAF and FAA.

The ADEN (named for the Armament Development Establishment, where it was designed, and Enfield, where it is produced) was developed in the late 1940s as a replacement for the older Hispano-Suiza HS 404 20 mm cannon used in British aircraft of World War II. It is based (as are the French DEFA and American M39 cannon) on the mechanism of the German Mauser MG 213C, an experimental revolver cannon designed for the Luftwaffe, but never used in combat. The ADEN entered service on the Hawker Hunter in 1954, and subsequently used on every British gun-armed aircraft until the advent of the Panavia Tornado in the 1980s.

The current version is the ADEN Mk 4. Although its muzzle velocity of 2,430 ft/s (741 m/s) is considerably lower than the Hispano's 2,789 ft/s (850 m/s), the substantially heavier projectile makes the ADEN more lethal, and it has a higher rate of fire of about 1,300 rounds per minute.

An improved version, the ADEN Mk 5, incorporates a multitude of small changes to improve reliability and increase rate of fire slightly to 1,500–1,700 rounds per minute. No new Mk 5s were built, but many older weapons were converted, being redesignated Mk 5 Straden.

Aircraft using the ADEN 30 as in-built armament have included the English Electric Lightning, Folland Gnat (and HAL Ajeet), Hawker Hunter, Gloster Javelin, Saab Lansen, Saab Draken, Supermarine Scimitar, and Australian versions of the F-86 Sabre. Several podded versions exist, including the installations scabbed below the fuselage of British Hawker Siddeley Harrier (and USMC AV-8A/Cs) and Sea Harriers and the Swedish FFV Aden, which is used (among others) on the BAe Hawk. The FFV Aden contains the weapon and 150 rounds of ammunition, is 151.57 in (3.85 m) long, and weighs 802.5 lb (364 kg) fully loaded.

The ADEN is very similar to the French DEFA cannon, and the two weapons use the same range of 30 mm ammunition.

The ADEN Mk 5 became the basis for the planned ADEN 25, which was to be a somewhat larger weapon (90 in / 2.29 m long, 203 lb / 92 kg) firing the new range of NATO 25 mm ammunition (as in the American GAU-12 Equalizer) at a much higher muzzle velocity of 3,445 ft/s (1,050 m/s). The lighter ammunition was also to produce a higher rate of fire, 1,650 to 1,850 rounds per minute. Unfortunately, severe development problems plagued the ADEN 25, which proved unable to meet its design weight target. It was finally cancelled in 1999. As a result, RAF Harrier GR.7 and GR.9 aircraft currently have no cannon, no attempt apparently having been made to retrofit the older ADEN 30 mm pods. Fleet Air Arm Sea Harriers retained the 30 mm weapon until their retirement in 2006.

• Type: single-barrel automatic cannon
• Caliber: 30 mm x 113 (1.18 in)
• Operation: revolver chamber
• Length: 1.59 m (62.6 in)
• Weight (complete): 87.1 kg (192 lb)
• Rate of fire: 1,200 - 1,700 rpm
• Muzzle velocity: 741 m/s (2,430 ft/s)
• Projectile weight: 220 g (7.76 oz)