M61 Vulcan The M61 Vulcan is a hydraulically or pneumatically driven , six - barrel , air - cooled , electrically fired Gatling - style rotary cannon which fires 20 mm rounds at an extremely high rate ( typically 6 , 000 rounds per minute ) . The M61 and its derivatives have been the principal cannon armament of United States military fixed - wing aircraft for fifty years . The M61 was originally produced by General Electric , and after several mergers and acquisitions is currently produced by General Dynamics . Development . At the end of World War II , the United States Army began to consider new directions for future military aircraft guns . The higher speeds of jet - powered fighter aircraft meant that achieving an effective number of hits would be extremely difficult without a much higher volume of fire . While captured German designs ( principally the Mauser MG 213 C ) showed the potential of the single - barrel revolver cannon , the practical rate of fire of such a design was still limited by ammunition feed and barrel wear concerns . The Army wanted something better , combining extremely high rate of fire with exceptional reliability . In 1947 , the Air Force became a separate branch of the military . The new Air Force made a request for a new aircraft gun . A lesson of World War II air combat was that German , Italian and Japanese fighters could attack American aircraft from long range with their cannon main armament . American fighters with . 50 cal main armament , such as the P - 51 and P - 47 , had to be close with the enemy in order to hit and damage enemy aircraft . The 20mm Hispano carried by the P - 38 while formidable against propeller driven planes was deemed a relatively low velocity weapon in the age of jets , while other cannon were notoriously unreliable . In response to this requirement , the Armament Division of General Electric resurrected an old idea : the multi - barrel Gatling gun . The original Gatling gun had fallen out of favor because of the need for an external power source to rotate the barrel assembly , but the new generation of turbojet - powered fighters offered sufficient electric power to operate the gun , and electric operation was more reliable than gas - operated reloading . With multiple barrels , the rate of fire per barrel could be lower than a single - barrel revolver cannon while providing greater overall rate of fire . The idea of powering a Gatling gun from an external electric power source was not a novel idea at the end of the World War II , as Richard Jordan Gatling himself had done just that in 1893 , with a patent he filed . In 1946 the Army issued General Electric a contract for " Project Vulcan " , a six - barrel weapon capable of firing 7 , 200 rounds per minute ( rpm ) . Although European designers were moving towards heavier 30 mm weapons for better hitting power , the U . S . initially concentrated on a powerful cartridge designed for a pre - war anti - tank rifle , expecting that the cartridge ' s high muzzle velocity would be beneficial for improving hit ratios on high speed targets . The first GE prototypes of the caliber T45 were ground - fired in 1949 ; it achieved 2 , 500 rpm , which was increased to 4 , 000 rpm by 1950 . By the early 1950s , the USAF decided that high velocity alone might not be sufficient to ensure target destruction and tested 20 mm and 27 mm alternatives based on the caliber cartridge . These variants of the T45 were known as the T171 and T150 respectively , and were first tested in 1952 . Eventually , the 20×102 mm cartridge was determined to have the desired balance of projectile and explosive weight and muzzle velocity . The development of the Lockheed F - 104 Starfighter revealed that the T171 Vulcan ( later redesignated " M61 " ) suffered problems with its linked ammunition , being prone to misfeed and presenting a foreign object damage ( FOD ) hazard with discarded links . A linkless ammunition feed system was developed for the upgraded " M61A1 " , which subsequently became the standard cannon armament of U . S . fighters . In 1993 , General Electric sold its aerospace division , including GE Armament Systems along with the design and production tooling for the M61 and GE ' s other rotary cannon , to Martin Marietta . After Martin ' s merger with Lockheed , the rotary cannon became the responsibility of Lockheed Martin Armament Systems . Lockheed Martin Armament Systems was later acquired by General Dynamics , who currently produce the M61 and its variants . Description . Each of the cannon ' s six barrels fires once in turn during each revolution of the barrel cluster . The multiple barrels provide both a very high rate of fire — around 100 rounds per second — and contribute to prolonged weapon life by minimizing barrel erosion and heat generation . Mean time between jams or failures is in excess of 10 , 000 rounds , making it an extremely reliable weapon . The success of the Vulcan Project and its subsequent progeny , the very - high - speed Gatling gun , has led to guns of the same configuration being referred to as " Vulcan cannon " , which can sometimes confuse nomenclature on the subject . Most aircraft versions of the M61 are hydraulically driven and electrically primed . The gun rotor , barrel assembly and ammunition feed system are rotated by a hydraulic drive motor through a system of flexible drive shafts . The round is fired by an electric priming system where an electric current from a firing lead passes through the firing pin to the primer as each round is rotated into the firing position . The self - powered version , the GAU - 4 ( called M130 in Army service ) , is gas - operated , tapping gun gas from three of the six barrels to operate the gun gas driven mechanism . The self - powered Vulcan weighs about more than its electric counterpart , but requires no external power source to operate , except for an electric , inertia starter to initiate gun rotation , allowing the first rounds to be chambered and fired . The initial " M61 " used linked , belted ammunition , but the ejection of spent links created considerable ( and ultimately insuperable ) problems . The original weapon was soon replaced by the " M61A1 " , with a linkless feed system . Depending on the application , the feed system can be either single - ended ( ejecting spent cases and unfired rounds ) or double - ended ( returning casings back to the magazine ) . A disadvantage of the M61 is that the bulk of the weapon , its feed system , and ammunition drum makes it difficult to fit it into a densely packed airframe . The feed system must be custom - designed for each application , adding to the complete weapon . Most aircraft installations are double - ended , because the ejection of empty cartridges can cause a foreign - object damage ( FOD ) hazard for jet engines and because the retention of spent cases assists in maintaining the center of gravity of the aircraft . The first aircraft to carry the M61A1 was the C model of the F - 104 , starting in 1959 . A lighter version of the Vulcan developed for use on the F - 22 Raptor , the " M61A2 " , is mechanically the same as the M61A1 , but with thinner barrels to reduce overall weight to . The rotor and housing have also been modified to remove any piece of metal not absolutely needed for operation and replaces some metal components with lighter weight materials . The F / A - 18E / F Super Hornet also uses this version . The Vulcan ' s rate of fire is typically 6 , 000 rounds per minute , although some versions ( such as that of the AMX and the F - 106 Delta Dart ) are limited to a lower rate , and others ( A - 7 Corsair ) have a selectable rate of fire of either 4 , 000 or 6 , 000 rounds per minute . The M61A2 ' s lighter barrels allow a somewhat higher rate of fire up to 6 , 600 rounds per minute . Ammunition . Practically no powered rotary cannon is supplied with sufficient ammunition for a full minute of firing , due to its weight . In order to avoid using the few hundred rounds carried in a matter of a single trigger pull , a burst controller is generally used to limit the number of rounds fired at each trigger pull . Bursts of from two or three up to 40 or 50 can be selected . The size of the airframe and available internal space limits the size of the ammunition drum and thus limits the ammunition capacity . Until the late 1980s the M61 primarily used the M50 series of ammunition in various types , typically firing a projectile at a muzzle velocity of about . A variety of Armor - Piercing Incendiary ( API ) , High Explosive Incendiary ( HEI ) , and training rounds are available . Around 1988 a new round was introduced , the PGU - 28 / B , which is now standard for US Navy and Air Force aircraft . The PGU - 28 / B is a " low - drag " round designed to reduce in - flight drag and deceleration , and has a slightly increased muzzle velocity of . The PGU - 28 / B is a semi - armor piercing high explosive incendiary ( SAPHEI ) round , providing substantial improvements in range , accuracy , and power over the preceding M56A3 HEI round . The PGU - 28 / B has not been without problems , however . A 2000 USAF safety report noted 24 premature detonation mishaps ( causing serious damage in many cases ) in 12 years with the SAPHEI round , compared to only two such mishaps in the entire recorded history of the M56 round . The report estimated that the current PGU - 28 / B had a potential failure rate 80 times higher than USAF standards permit . The main types of combat rounds and their main characteristics are listed in the table below . Applications and first combat use . The Vulcan first entered aerial combat on 4 April 1965 when four North Vietnamese Air Force MiG - 17s ( J - 5 s ) attacked a force of 10 escorting North American F - 100 Super Sabre s ( 2 of which were assigned weather reconnaissance duties ) and 48 Vulcan armed , but " bomb - laden F - 105 s " , shooting down two Thunderchiefs . The MiG Leader , Capt . Tran Hanh , and the only survivor from the 4 MiGs reported that U . S . jets had pursued them and that F - 105s had shot down 3 of his aircraft , killing Lieutenant s Pham Giay , Le Minh Huan , and Tran Nguyen Nam . Capt . Donald Kilgus piloting an F - 100 did receive an official probable kill with his four M39 20mm cannons during the engagement ; however no other US pilot reported destroying any MiGs during the battle , leaving open the plausibility that at least 2 of the MiG - 17s may have been downed by their own AA fire . The first confirmed Vulcan gun kill occurred on 29 June 1966 when Major Fred Tracy , flying his F - 105 Thunderchief with the 421st TFS , fired 200 rounds of 20mm into a MiG - 17 that had just fired a 23mm shell through one side of his cockpit and which exited out the other side . When the NVAF MiG flew in front of him after making his pass , Maj . Tracy opened fire on him . The gun was installed in the Air Force ' s A - 7D version of the LTV A - 7 Corsair II where it replaced the earlier United States Navy A - 7 ' s Colt Mk 12 cannon and was adopted by the Navy on the A - 7C and A - 7E . It was integrated into the newer F - 4E Phantom II variants . The F - 4 was originally designed without a cannon as it was believed that missiles had made guns obsolete . Combat experience in Vietnam showed that a gun could be more effective than guided missiles in many combat situations , and that an externally carried gun pod was less effective than an internal gun ; the first generation of gun pods such as the SUU - 16 were not oriented with the sights of the fighter . The improved pods were self - powered and properly synchronized to the fighters sights . The next generation of fighters built post - Vietnam incorporated the M61 gun internally . The Vulcan was later fitted into the weapons bay of some Convair F - 106 Delta Dart and General Dynamics F - 111 Aardvark models . It was also adopted as standard in the " teen " - series air superiority fighters , the Grumman F - 14 Tomcat , the McDonnell Douglas F - 15 Eagle , General Dynamics F - 16 Fighting Falcon and McDonnell Douglas F / A - 18 Hornet . Other aircraft include the Italian / Brazilian AMX International AMX ( on Italian aircraft only ) , and the F - 22 Raptor . It was fitted in a side - firing installation on the Fairchild AC - 119 , some marks of the Lockheed AC - 130 gunship s , and was used in the tail turrets of both the Convair B - 58 Hustler and Boeing B - 52H Stratofortress bomber s . Japan ' s Mitsubishi F - 1 carried one internally mounted JM61A1 Vulcan with 750 rounds . Two gun pod versions , the SUU - 16 / A ( also designated M12 by the US Army ) and improved SUU - 23 / A ( US Army M25 ) , were developed in the 1960s , often used on gunless versions of the F - 4 . The SUU - 16 / A uses the electric M61A1 with a ram - air turbine to power the motor . This proved to cause serious aerodynamic drag at higher speeds , while speeds under did not provide enough airflow for maximum rate of fire . The subsequent SUU - 23 / A uses the " GAU - 4 / A " self - powered Vulcan , with an electric inertia starter to bring it up to speed . Both pods ejected empty cases and unfired rounds rather than retaining them . Both pods contained 1 , 200 rounds of ammunition , with a loaded weight of respectively . During service in the Vietnam War the pods proved to be relatively inaccurate : the pylon mounting was not rigid enough to prevent deflection when firing , and repeated use would misalign the pod on its pylon , making matters worse . A variant with much shorter barrels , designated the M195 , was also developed for use on the M35 Armament Subsystem for use on the AH - 1G Cobra helicopter . This variant fed from ammunition boxes fitted to the landing skid and was developed to provide the AH - 1 helicopter with a longer - range suppressive fire system before the adoption of the M97 Universal Turret mounting the M197 cannon . The M61 is also the basis of the US Navy Mk 15 Phalanx Close - in weapon system system and the M163 VADS Vulcan Air Defense System , using the M168 variant .