The M197 electric cannon is a three-barreled electric Gatling gun

Gatling gun

The Gatling gun is one of the best known early rapid-fire weapons and a forerunner of the modern machine gun. It is well known for its use by the Union forces during the American Civil War in the 1860s, which was the first time it was employed in combat...

 developed primarily for use by United States Army

United States Army

The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

 helicopter

Military helicopter

A military helicopter is a helicopter that is either specifically built or converted for use by military forces. A military helicopter's mission is a function of its design or conversion...

 gunship

Gunship

The term "gunship" is used in several contexts, all sharing the general idea of a light craft armed with heavy guns.-In Navy:In the Navy, the term originally appeared in the mid-19th century as a less-common synonym for gunboat.-In military aviation:...

s.

Development of the M197 began in 1967

1967 in aviation

This is a list of aviation-related events from 1967:- Events :* The Canadian Golden Centennaires aerobatic team is formed and performs all year to celebrate the Canadian centennial year....

 after experience in the Vietnam War

Vietnam War

The Vietnam War was a Cold War-era military conflict that occurred in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. This war followed the First Indochina War and was fought between North Vietnam, supported by its communist allies, and the government of...

 revealed the inadequacy of the 7.62 mm Minigun

Minigun

The Minigun is a 7.62 mm, multi-barrel heavy machine gun with a high rate of fire , employing Gatling-style rotating barrels with an external power source...

 for gunship use. The M197 is essentially a lightened version of the General Electric M61 Vulcan

M61 Vulcan

The M61 Vulcan is a hydraulically or pneumatically driven, six-barreled, air-cooled, electrically fired Gatling-style rotary cannon which fires 20 mm rounds at an extremely high rate. The M61 and its derivatives have been the principal cannon armament of United States military fixed-wing aircraft...

 cannon, with three barrels

Gun barrel

A gun barrel is the tube, usually metal, through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out of the end at a high velocity....

 instead of six. Its maximum rate of fire

Rate of fire

Rate of fire is the frequency at which a specific weapon can fire or launch its projectiles. It is usually measured in rounds per minute , or per second .-Overview:...

 is one quarter that of the Vulcan, largely to limit its recoil

Recoil

Recoil is the backward momentum of a gun when it is discharged. In technical terms, the recoil caused by the gun exactly balances the forward momentum of the projectile and exhaust gasses, according to Newton's third law...

 for light aircraft and helicopter use. It shares the Vulcan's M50 and PGU series 20 mm ammunition

Ammunition

Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...

.

The M197 went into service on later marks of the AH-1 Cobra

AH-1 Cobra

The Bell AH-1 Cobra is a two-bladed, single engine attack helicopter manufactured by Bell Helicopter. It shares a common engine, transmission and rotor system with the older UH-1 Iroquois...

, using either the M97 or A/A49E-7 armament subsystems, and was also fitted in a ventral turret

Gun turret

A gun turret is a weapon mount that protects the crew or mechanism of a projectile-firing weapon and at the same time lets the weapon be aimed and fired in many directions.The turret is also a rotating weapon platform...

 on the U.S. Marine Corps YOV-10D Bronco NOGS

OV-10 Bronco

The North American Aviation Rockwell OV-10 Bronco is a turboprop light attack and observation aircraft. It was developed in the 1960s as a special aircraft for counter-insurgency combat, and one of its primary missions was as a forward air control aircraft...

. It is also the basis of the GPU-2/A

U.S. aircraft gun pods

The idea of the gun pod as a concept largely came into its prime during and period following World War II. So-called "package gun" installations on US medium and light bombers, such as the B-25 Mitchell and A-26 Invader, were probably the first such attempts by the United States military...

gun pod

Gun pod

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

, which incorporates the cannon, a battery

Battery (electricity)

An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

 and electric drive motor

Electric motor

An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

, and 300 rounds of linkless ammunition.

In the Cobra, the weapon is supplied with a magazine of 700 linked rounds, with a total capacity including feeder system of 750 rounds. It has a cyclic rate of fire of 650 rounds per minute. Standard practice is to fire the cannon in 30 to 50-round bursts.

The M197 remains in use in the latest AH-1W and AH-1Z Cobra gunships. Although the weapon's rotary drive is theoretically quite reliable, its ammunition feed has been anything but: Marine pilots initially reported an alarmingly high jam rate (sometimes greater than 30%). The USMC and the manufacturer are aware of the problem and in 2011 a link less feed system developed by Meggit Defense Systems was incorporated into the AH-1W and the Zulu's. The system is capable of holding 650 +/-3 rounds in the storage unit with approximately 40 rounds in the feed chute.

The M197 is also mounted as a chin turret in Italy's Agusta A129 Mangusta CBT helicopter, with a capacity of 500 rounds.

The weapon's current contractor is General Dynamics Armament Systems.

Ammunition

Designation	Type	Projectile Weight [g]	Bursting charge [g]	Muzzle Velocity [m/s]	Description
M53	API	?	4.2 g incendiary	1030	Penetration 6.3 mm RHA at 0-degree impact and 1000-m range.
M56A3/A4	HEI	102	9 g HE (RDX/wax/Al) and 1.5 g incendiary	1030	Nose fuzed round, no tracer. Effective radius to produce casualties to exposed personnel 2 meters, fragmentation hazard out to 20 meters. Penetration 12.5 mm RHA at 0 degree obliquity at 100m range
M242	HEI-T	?	?	?	Similar to M56 series of HEI rounds, but with a tracer element.
M246	HEI-T	102	8.0 g HE	?	Nose fuzed tracer round fired by M168 AA gun, self-destruct after 3 to 7 seconds of flight due to tracer burn-through.
M940 M-940 20mm MPT-SD Round The M-940 is a 20 mm round produced by General Dynamics primarily for an anti-aircraft role. It has a range of over and a multi-purpose warhead with high explosive and incendiary effects. The round includes a red tracer to aid in targeting. The self-destruct feature engages at approx...	MPT-SD	105	9 g A-4/RDX/wax	1050	Multi-purpose fuzeless round, HE charge is initiated by the incendiary charge on the nose on impact. Self-destruct due to tracer burn-through. Penetration 12.5 mm RHA at 0 degree impact at 518 m range, or 6.3 mm at 60 degrees and 940 m.