GAU-12 Equalizer

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GAU-12/U Equalizer
Type Rotary cannon
Place of origin United States
Production history
Designer General Dynamics
Weight 270 lb (122 kg)
Length 83.2 in (2.11 m)
Width 10 in (256 mm)
Height 11.5 in (292 mm)

Cartridge 25 x 137 mm
Caliber 25 mm (0.98 in)
Barrels 5-barrel (progressive RH parabolic twist, 11 grooves)
Action Hydraulic, Electric, Pneumatic
Rate of fire 1800–4200 rounds per minute
Muzzle velocity (HEI) 3400 ft/s (1040 m/s); (API) 3280 ft/s (1000 m/s).
Maximum firing range 12,000 feet (3,660 m)
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-type 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. For use in the AC-130 gunship, the fire rate is limited to 1,800 rounds per minute in order to conserve ammunition and reduce barrel wear.


An AV-8 Harrier II; the two pods on the belly of the aircraft hold the cannon (port side, visible hole) and ammunition (starboard side).

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 did not adopt 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 were without gun armament until retirement.[citation needed]

The Equalizer is also used in the AC-130U Spooky 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 Equalizer was also used as the basis for the Sea Vulcan 25, a turret mounted gun for naval ship self-defense, although not as a Close-In Weapon System, as the gun was not automatic nor did it use radar tracking. Instead the gun was manually aimed using a digital gun sight and fire control. Sea Vulcan consisted a 540 round helical drum magazine, a one-piece aluminum turret that can be opened with just a screwdriver, and the main gun. One unique advantage of the system was that it was capable of operating independently of ships power; the gun and ammunition magazine were powered by a 3,000 psi pneumatic drive and the turret motor by twin lead-acid batteries. Using the Navy's Mk 24 target designator and laser range finder. Meant as a higher firepower alternative to typical machine guns mounted on deck. The gun was developed in the mid 1980s as a cost effective protection for ships smaller than frigate or corvette or patrol boats but did not enter service.

The GAU-12 was utilized as the principal armament for the Rutan ARES.


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.[1] The CTOL version of the aircraft will carry the gun internally, while the STOVL and CV versions use it as an external podded gun. The GAU-22/A's major difference is the use of four barrels, rather than the five barrels on the GAU-12/U. The GAU-22/A is lighter, has a reduced rate of fire of 3,300 rounds per minute and an improved accuracy of 1.4 milliradians as compared to the GAU-12.[2] This system is undergoing intensive testing and qualification. The weapon is currently produced by General Dynamics Ordnance and Tactical Systems.

The Nammo 25 mm APEX projectile is being developed for the GAU-22/A.[3]

Specifications (GAU-12)

GAU-12/U gun test firing
  • Type: Five-barreled rotary cannon
  • Caliber: 25 mm (0.98 in)
  • Operation: electric
  • Length: 83.2 in (2.11 m)
  • Weight (complete): 270 lb (122 kg)
  • Rate of fire: 3,600–4,200 rounds per minute
  • Muzzle velocity: (HEI) 3,400 ft/s (1,040 m/s); (API) 3,280 ft/s (1,000 m/s)
  • Projectile weight: (HEI) 6.5 oz (184 g); (API) 7.6 oz (215 g)
  • Muzzle energy: (HEI) 73,400 ft·lbf (99,500 joules); (API) 79,300 ft·lbf (107,500 joules)


  1. Maher, Dave (2006-03-30). "25mm Gun Systems for the F-35 Joint Strike Fighter" (PDF). National Defense Industrial Association. Retrieved 2008-10-14.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  2. GAU-22/A fact sheet. General Dynamics
  3. "Norway contracts for F-35 ammunition." UPI, 29 November 2010.

External links