The General Dynamics GAU-12/U Equalizer is a five-barrel 25 mm Gatling-type

rotary cannon A rotary cannon, rotary autocannon, rotary gun or Gatling cannon, is any large- caliber multiple-barreled automatic firearm that uses a Gatling-type rotating barrel assembly to deliver a sustained saturational direct fire at much greater r ...

. The GAU-12/U is used by the United States, Italy and Spain, which mount the weapon in their attack jets such as the

AV-8B Harrier II The McDonnell Douglas (now Boeing) AV-8B Harrier II is a single-engine ground-attack aircraft that constitutes the second generation of the Harrier family, capable of vertical or short takeoff and landing (V/STOL). The aircraft is primari ...

, airborne

gunship A gunship is a military aircraft armed with heavy aircraft guns, primarily intended for attacking ground targets either as airstrike or as close air support. In modern usage the term "gunship" refers to fixed-wing aircraft having laterally-m ...

s such as the

Lockheed AC-130 The Lockheed AC-130 gunship is a heavily armed, long-endurance, attack aircraft, ground-attack variant of the C-130 Hercules transport, fixed-wing aircraft. It carries a wide array of ground-attack weapons that are integrated with sophisticate ...

, and land-based fighting vehicles. A lighter four-barrel version, designated GAU-22/A, is mounted on

F-35 Lightning II The Lockheed Martin F-35 Lightning II is an American family of single-seat, single-engine, all-weather stealth multirole combat aircraft that is intended to perform both air superiority and strike missions. It is also able to provide elect ...

fighter jets.

Development

The five-barrel Equalizer cannon was developed in the late 1970s, based on the mechanism of the 30mm

GAU-8/A Avenger The General Electric GAU-8/A Avenger is a 30 mm hydraulically driven seven-barrel Gatling-style autocannon that is primarily mounted in the United States Air Force's Fairchild Republic A-10 Thunderbolt II. Designed to destroy a wide variety of g ...

cannon, but firing a new

NATO The North Atlantic Treaty Organization (NATO, ; french: Organisation du traité de l'Atlantique nord, ), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two N ...

series of 25 mm ammunition. The GAU-12/U cannon is operated by an 11 kW (15 hp)

electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate f ...

, or in external mounts supplied by a

bleed air Bleed air is compressed air taken from the compressor stage of a gas turbine upstream of its fuel-burning sections. Automatic air supply and cabin pressure controller (ASCPCs) valves bleed air from high or low stage engine compressor sections. Lo ...

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 The Lockheed AC-130 gunship is a heavily armed, long-endurance, ground-attack variant of the C-130 Hercules transport, fixed-wing aircraft. It carries a wide array of ground-attack weapons that are integrated with sophisticated sensors, naviga ...

gunship, the fire rate is limited to 1,800 rounds per minute in order to conserve ammunition and reduce barrel wear.

GAU-22/A

The GAU-22/A is a four-barrel version of the GAU-12/U designed for use on the

. The GAU-22/A's major difference is the use of four barrels, rather than the GAU-12/U's five barrels. The GAU-22/A is lighter and has a reduced rate of fire of 3,300 rounds per minute, but maintains the same, high accuracy of 5

milliradian A milliradian ( SI-symbol mrad, sometimes also abbreviated mil) is an SI derived unit for angular measurement which is defined as a thousandth of a radian (0.001 radian). Milliradians are used in adjustment of firearm sights by adjusting t ...

s, 80% circle of the GAU-12 and A-10's GAU-8. The weapon is produced by

General Dynamics General Dynamics Corporation (GD) is an American publicly traded, aerospace and defense corporation headquartered in Reston, Virginia. As of 2020, it was the fifth-largest defense contractor in the world by arms sales, and 5th largest in the Uni ...

Ordnance and Tactical Systems. The

Nammo Nammo, short for Nordic Ammunition Company, is a Norwegian/Finnish aerospace and defence group specialized in production of ammunition, rocket engines and space applications. The company has subsidiaries in Finland, Germany, Norway, Sweden, Switze ...

25 mm PGU-47/U

APEX The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics), a teenaged super villainess in the Marvel Universe * Ape-X, a super-intelligent ape in the Squadron Supreme universe *Apex, ...

(Armor Piercing with Explosive) projectile has been developed for the GAU-22/A."Norway contracts for F-35 ammunition."
''UPI'', 29 November 2010. It features a tungsten carbide penetrator in the tip and an explosive fragmentation body, to be multi-purpose against both hardened and soft targets. Also, the presence of a clockworking inertia-driven mechanical

fuze In military munitions, a fuze (sometimes fuse) is the part of the device that initiates function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fuze ...

in the mid-body, protects the round from shocks, misfires and cookoffs, making it safer to handle and fire.

Uses

The current principal application for the Equalizer is the

AV-8 Harrier II The McDonnell Douglas (now Boeing) AV-8B Harrier II is a single-engine ground-attack aircraft that constitutes the second generation of the Harrier family, capable of vertical or short takeoff and landing (V/STOL). The aircraft is primaril ...

s of the

United States Marine Corps The United States Marine Corps (USMC), also referred to as the United States Marines, is the maritime land force service branch of the United States Armed Forces responsible for conducting expeditionary and amphibious operations through c ...

Italian Navy "Fatherland and Honour" , patron = , colors = , colors_label = , march = ( is the return of soldiers to their barrack, or sailors to their ship after a ...

and

Spanish Navy The Spanish Navy or officially, the Armada, is the maritime branch of the Spanish Armed Forces and one of the oldest active naval forces in the world. The Spanish Navy was responsible for a number of major historic achievements in navigation, ...

. The Harrier II carries the Equalizer system in a pair of detachable pods mounted on the fuselage underside, 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 (unlike previous Harriers which used dual cannons, with each pod containing a

30mm 30 mm caliber is a specific size of popular autocannon ammunition. Such ammunition includes NATO standard 30×113mmB and 30×173mm (STANAG 4624), Soviet 30×155mmB, 30×165mm, and 30×210mmB, Yugoslav 30×192mm, Anglo-Swiss 30×170mm, and ...

ADEN gun and its own ammunition supply). The complete installation, which includes a double-ended feed system that returns empty cartridges to the

magazine A magazine is a periodical publication, generally published on a regular schedule (often weekly or monthly), containing a variety of content. They are generally financed by advertising, purchase price, prepaid subscriptions, or by a combinatio ...

, weighs 900 lb (410 kg) empty and 1,230 lb (560 kg) loaded. The detachable pods are located and shaped to be interchangeable with the usual ventral strakes or fences under the Harrier, both serving to help trap a cushion of high-pressure air under the aircraft to add lift while in hover mode. The strakes can easily be removed and the pods attached in their place, serving the same function while adding useful firepower.

RAF The Royal Air Force (RAF) is the United Kingdom's air and space force. It was formed towards the end of the First World War on 1 April 1918, becoming the first independent air force in the world, by regrouping the Royal Flying Corps (RFC) and ...

and

Fleet Air Arm The Fleet Air Arm (FAA) is one of the five fighting arms of the Royal Navy and is responsible for the delivery of naval air power both from land and at sea. The Fleet Air Arm operates the F-35 Lightning II for maritime strike, the AW159 Wi ...

Harriers did not adopt the Equalizer for their

Harrier GR7 The British Aerospace Harrier II is a second-generation vertical/short takeoff and landing (V/STOL) jet aircraft used previously by the Royal Air Force (RAF) and, between 2006 and 2010, the Royal Navy (RN). The aircraft was the latest developm ...

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 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 po ...

). That gun was canceled in

1999 File:1999 Events Collage.png, From left, clockwise: The funeral procession of King Hussein of Jordan in Amman; the 1999 İzmit earthquake kills over 17,000 people in Turkey; the Columbine High School massacre, one of the first major school shoot ...

after protracted development problems, and British Harrier GR7/9s were without gun armament until retirement. The Equalizer is also used in the AC-130U Spooky

, where one cannon is mounted on the port side, and the

U.S. Marine Corps The United States Marine Corps (USMC), also referred to as the United States Marines, is the maritime land force service branch of the United States Armed Forces responsible for conducting expeditionary and amphibious operations through co ...

LAV-AD air-defense vehicle. Other applications have been planned for the GAU-12/U, including a mounting for the

AH-1 Cobra The Bell AH-1 Cobra is a single-engined attack helicopter developed and manufactured by the American rotorcraft manufacturer Bell Helicopter. A member of the prolific Huey family, the AH-1 is also referred to as the HueyCobra or Snake. The AH ...

attack helicopter An attack helicopter is an armed helicopter with the primary role of an attack aircraft, with the offensive capability of engaging ground targets such as enemy infantry, military vehicles and fortifications. Due to their heavy armament they ...

. 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 A close-in weapon system (CIWS ) is a point-defense weapon system for detecting and destroying short-range incoming missiles and enemy aircraft which have penetrated the outer defenses, typically mounted on a naval ship. Nearly all classes of l ...

, 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 of 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 ship's power; the gun and ammunition magazine were powered by a 3,000 psi pneumatic drive and the turret motor by twin lead–acid batteries. Intended as a higher-firepower alternative to conventional deck-mounted machine guns and cannon, the weapon employs the Navy's Mk 24 target designator and laser range finder for enhanced accuracy. 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 this service. The GAU-12 was utilized as the principal armament for the Rutan ARES. The four-barrel GAU-22 is carried internally by the F-35A (the

CTOL A conventional take-off and landing (CTOL), also known as horizontal take-off and landing (HTOL) is the process whereby conventional fixed-wing aircraft (such as passenger aircraft) take off and land, involving the use of runways. During takeoff ...

version of the F-35) on the port side of the fuselage, with 180 PGU-47/U APEX rounds. In contrast, the F-35B

STOVL A short take-off and vertical landing aircraft (STOVL aircraft) is a fixed-wing aircraft that is able to take off from a short runway (or take off vertically if it does not have a heavy payload) and land vertically (i.e. with no runway). The ...

and C naval aircraft mount the GAU-22 in a stealthy external

gun pod A gun pod is a detachable pod or pack containing machine guns, autocannons, revolver cannons, or rotary cannons and ancillaries, mounted externally on a vehicle such as a military aircraft which may or may not also have its own guns. Descriptio ...

under the fuselage, together with 220 rounds.

Specifications (GAU-12/U)

*Type: Five-barreled

*Caliber: 25 mm (0.98 in) *Operation:

electric Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...

*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)

Specifications (GAU-22/A)

*Type: Four-barreled rotary cannon *Caliber: 25 mm (0.98 in) *Operation: electric *Length: 83.2 in (2.11 m) *Weight (complete): 230 lb (104 kg) *Rate of fire: 3,300 rounds per minute *Muzzle velocity: (APEX) 3,200 ft/s (970 m/s) *Projectile weight: (APEX) 7.87 oz (223 g) *Muzzle energy: (APEX) 77,400 ft·lbf (104,900 joules)

Similar systems

Gryazev-Shipunov GSh-6-23 The Gryazev-Shipunov GSh-6-23 (russian: Грязев-Шипунов ГШ-6-23) (GRAU designation: 9A-620 for GSh-6-23, 9A-768 for GSh-6-23M modernized variant) is a six-barreled 23 mm rotary cannon used by some modern Soviet/Russian military ...

Myriad CIWS Myriad CIWS was a twin 7 barrelled, 25 mm rotary cannon-style CIWS developed by a consortium including Oto Melara. The system's primary purpose, had it ever gone into production, would have been defense against anti-ship missiles, and other ...

References

External links

General Dynamics Ordnance and Tactical Systems GAU-12/U page

F-35 JSF gun system page on General Dynamics Armament and Technical Products (manufacturer) site

Sea Vulcan archive Video
{{DEFAULTSORT:Gau-12 Equalizer Rotary cannon Multi-barrel machine guns Aircraft guns Articles containing video clips 25 mm artillery Military equipment introduced in the 1970s