|Place of origin||United States|
|Weight||270 lb (122 kg)|
|Length||83.2 in (2.11 m)|
|Width||10 in (256 mm)|
|Height||11.5 in (292 mm)|
|Caliber||25 mm (0.98 in)|
|Action||Hydraulic, Electric, Pneumatic|
|Rate of fire||3600 - 4200 rounds per minute|
|Muzzle velocity||(HEI) 3400 ft/s (1040 m/s); (API) 3280 ft/s (1000 m/s).|
|Feed system||Linked or linkless|
|Sights||Lead Computing Optical Sight System (LCOSS)|
The General Dynamics GAU-12/U Equalizer is a five-barrel 25 mm Gatling gun-style rotary cannon. The GAU-12/U is used by the United States, Italy and Spain, which mount the weapon in their fighter jets such as the AV-8B Harrier II, airborne gunships such as the Lockheed AC-130, and land-based fighting vehicles.
The five-barrel 'Equalizer' cannon was developed in the late 1970s, based on the mechanism of the GAU-8/A Avenger cannon, but firing a new NATO series of 25 mm ammunition. The GAU-12/U cannon is operated by a 15 hp (11 kW) electric motor, in external mounts supplied by a bleed air driven pneumatic system. Its rate of fire is normally 3,600 rounds per minute, with a maximum of 4,200 rounds per minute.
The Equalizer normally uses PGU-20/U armor-piercing incendiary (API) or PGU-22 or PGU-25 high explosive incendiary (HEI) ammunition. With a harder-hitting projectile and comparable muzzle velocity, it is more lethal than the older M61 Vulcan, and more effective than the older 30 mm ADEN cannon it replaces.
The current principal application for the Equalizer is the AV-8 Harrier IIs of the United States Marine Corps, Italian Navy and Spanish Navy. The Harrier II carries the Equalizer system in a pair of pods mounted on the fuselage sides, with the cannon in the port pod and 300 rounds of ammunition in the starboard pod, fed through a bridge at the aft ends of the pods that also contains the drive system for the gun. The complete installation, which includes a double-ended feed system that returns empty cartridges to the magazine, weighs 900 lb (410 kg) empty and 1,230 lb (560 kg) loaded.
RAF and Fleet Air Arm Harriers have not adopted the Equalizer for their Harrier GR7 and GR9s. The British had originally planned a pair of ADEN 25 guns (using the same ammunition as the GAU-12/U, but based on the 30 mm ADEN cannon). That gun was canceled in 1999 after protracted development problems, and British Harrier GR7/9s are without gun armament.
The Equalizer is also used in the AC-130U Spectre gunship, where one cannon is mounted on the port side, and the U.S. Marine Corps LAV-AD air-defense vehicle. Other applications have been planned for the GAU-12/U, including a mounting for the AH-1 Cobra attack helicopter.
The GAU-22/A is the latest application of the GAU-12/U, which is a four barrel version designed for use on the F-35 Lightning II. In the CTOL version of the aircraft it will carry the gun internally, while on the STOVL and CV versions an external podded gun will be available. The major difference between the GAU-12/U and the GAU-22/A is the use of a four barrel system, rather than the five barrels on the standard GAU-12/U. The four barrel version is purported to reduce weight and improve accuracy. This system is currently undergoing intensive testing and qualification. The weapon's current contractor is General Dynamics Armament and Technical Products.
Test firing of GAU-22 gun