The L21A1 RARDEN ("Royal Armament, Research and Development Establishment" and "Enfield") is a British 30mm autocannon used as a combat vehicle weapon. The Royal Armament Research and Development Establishment (RARDE) and the Royal Small Arms Factory (RSAF), Enfield, at the time, were both part of the Ministry of Defence.
The weapon uses a long recoil system of operation, for minimum recoil forces on the mounting and vehicle. Spent cases are ejected forwards. The weapon was also designed for minimum inboard length, allowing for more space in the turret or a smaller turret overall. Another feature is that no gun gas escapes into the turret.
The cartridge case used is 170mm in length, and is based on the Hispano-Suiza 831-L round. Unlike the belt-fed or drum-fed systems on many vehicle weapons, Rarden is loaded manually with three-round clips. Each three-round clip is loaded into the magazine as a unit, similar to the 5-round clips of the Bofors 40 mm cannon. The magazine can hold two 3-round clips at a time. This limits its capacity to fire in automatic mode to 6 rounds. The Rarden gun does not require an external power source and can therefore remain in action even if the vehicle is disabled, provided that provision is made for manual traverse and elevation of the turret or mount and for sighting the weapon.
The RSAF Enfield manufactured the Rarden from the early 1970s. However the RSAF was incorporated within the Royal Ordnance Factories in the early 1980s, in the run up to their privatisation, becoming part of Royal Ordnance. Royal Ordnance (RO) planned to close Enfield and several other sites after privatisation. British Aerospace (BAe) bought Royal Ordnance on 2 April 1987 and the closure of RSAF Enfield was announced on 12 August 1987. Most of RO Enfield's work was moved, prior to the closure of the RSAF, to RO Nottingham.
Manufacture of the RARDEN was carried out at British Manufacture and Research Company BMARC from 1985. This company was purchased by BAe in 1992, becoming part of RO Defence; this organisation is now renamed BAE Systems Global Combat Systems Munitions.
The Rarden is, or has been, fitted to a number of armoured vehicles in the British Army:
- FV721 Fox armoured car
- FV107 Scimitar tracked reconnaissance vehicle (part of the Combat Vehicle Reconnaissance (Tracked) or CVR(T) range)
- Sabre — FV101 Scorpion with turrets taken from Fox Armoured cars (also in the CVR(T) range)
- FV510 Warrior infantry fighting vehicle, and some of its variants
The Rarden was also intended to be retro-fitted to the FV432 armoured personnel carrier, but when fitted with Rarden and its turret there was too little room left to accommodate the necessary infantry. 13 vehicles were fitted with the Fox turret, as an experimental fire support vehicle. There were problems with the long-barrelled weapon fouling external fittings (which meant that the turret had to be mounted on a three-inch spacer) and with blast damage to the flotation screen. They were deployed with the Berlin Infantry Brigade.
In March 2008, the UK Ministry of Defence announced that a 40mm weapon firing Cased Telescoped Ammunition developed by the Anglo-French firm CTA International had been selected to replace Rarden in the Warrior IFV and to be fitted to the reconnaissance vehicle which would replace the existing range of CVR(T) vehicles.
- Cartridge: 30×170mm
- Calibre: 30mm
- Overall length: 3.15 metres (10 ft 4 in)
- Barrel length: 2.44 metres (8 ft 0 in)
- Inboard length: 430 millimetres (17 in)
- Complete weight: 110 kilograms (240 lb)
- Barrel weight: 24.5 kilograms (54 lb)
- Ammunition: Armour Piercing Secondary Effect (APSE), High Explosive Incendiary (HEI), Armour Piercing Discarding Sabot (APDS)
- Muzzle velocity:
- APSE, HEI: 1070 m/s
- APDS: 1175 m/s
- Range: 2,000 metres (2,200 yd) 
- Hobart, Major F.W.A. (January–February 1974). "The RARDEN Cannon". Armor. pp. 18–24.
- "Jane's Ammunition Handbook: 30 x 170 Rarden gun ammunition, Cannon - 20 to 30 mm cannon". Jane's. Archived from the original on 26 January 2013. Retrieved 30 September 2010.
- Terry Gander, Encyclopaedia of the Modern British Army, Terry Gander, Guild Publishing, 1980 (p.181)
- Dabrowski, Christopher. "Land Vehicles/ Military Transport: Replacing the Rarden". Defence Management Journal. PSCA International (39). Archived from the original on 9 July 2011. Retrieved 30 September 2010.