Rotary cannon A rotary ( auto ) cannon , or Gatling - type auto - cannon , is a rapid - firing weapon that utilizes multiple barrels in a rotating cluster to provide a sustained rate of fire greater than single - barrelled machine guns or automatic cannons of equivalent caliber . The loading , firing , and unloading functions are performed simultaneously in different barrels as they rotate , and the rotation also permits the barrels some time to cool . The rotating barrel cluster on most Gatling - type guns is powered by an external force such as an electric motor , although gas - operated versions have also been developed . The cyclic multi - barrel design synchronizes the firing / reloading sequence . Each barrel fires a single shot when it reaches a certain point in the cycle , after which the spent cartridge is ejected and then a new round loaded . During the cycle , the barrel transfers some heat to the surrounding air . History . The original rotary cannon was the Gatling gun , designed by the American inventor Dr . Richard J . Gatling in 1861 and patented in 1862 . Hand cranked and hopper fed , it could fire at a rate of 200 rounds per minute . The Gatling gun was a field weapon , first used in warfare during the American Civil War and subsequently by European and Russian armies . The design was steadily improved ; by 1876 the Gatling gun had a theoretical rate of fire of 1 , 200 rounds per minute , although 400 rounds per minute was more readily achievable in combat . By 1893 , the M1893 Gatling gun was capable of a maximum rate of fire of some 800 – 900 rounds per minute . Ultimately the Gatling ' s weight and cumbersome artillery carriage hindered its ability to keep up with infantry forces over difficult ground and was superseded by lighter and more mobile machine - guns . All models of Gatling guns were declared obsolete by the U . S . Army in 1911 , after 45 years of service . Development of modern Gatling - type guns . After the Gatling gun was replaced in service by newer recoil - or gas - operated non - rotating machine guns , the approach of using multiple rotating barrels fell into disuse for many decades . However , some examples were developed during the interwar years but only existed as prototypes , or rarely used . During World War I , Imperial Germany was working on the Fokker - Leimberger , an externally powered 12 - barrel Gatling gun in the 7 . 92x57mm round capable of firing over 7200 rounds per minute . After World War II , the U . S . Army Air Force determined that an automatic cannon of improved design with an extremely high rate of fire was required to achieve a sufficient number of large - caliber hits on fast - moving enemy jet aircraft . Using experience gained from 20mm and 30mm cannon utilized by " Luftwaffe " aircraft , a larger - caliber cannon shell for the new gun was deemed desirable , as it contained room for an explosive with more destructive force than the . 30 and . 50 caliber machine gun cartridges previously employed , and thus capable of destroying aircraft with only a few hits on target . In June 1946 , the General Electric Company was awarded a U . S . military defense contract to develop an aircraft gun with a high rate of fire which GE termed " Project Vulcan " . While researching prior work , ordnance engineers recalled the experimental electrically driven Gatling weapons of the turn of the 20th century . In 1946 , a Model 1903 Gatling gun borrowed from a museum was set up with an electric motor drive and test - fired by General Electric engineers . The 40 - year - old design briefly managed a rate of fire of 5 , 000 rounds per minute . In 1949 General Electric began testing the first model of its modified Gatling design , now called the " Vulcan Gun " . The first prototype was designated the T45 ( Model A ) . It fired ammunition at about 2 , 500 rounds per minute , from six barrels driven by an electric motor . In 1950 , GE delivered ten initial model A . 60 cal . T45 guns for evaluation . Thirty - three model C T45 guns were delivered in 1952 in three calibers : . 60 cal . , 20mm , and 27mm , for additional testing . After extensive testing , the T171 20mm gun was selected for further development . In 1956 , the T171 20mm gun was standardized by the U . S . Army and U . S . Air Force as the M61 20mm Vulcan aircraft gun . One of the main reasons for the resurgence of the electrically or hydraulically powered multiple - barrel design is the weapon ' s tolerance for continuous high rates of fire . For example , 1000 rounds per minute of continuous fire from a conventional single - barrel weapon ordinarily results in rapid barrel heating followed by stoppages caused by overheating . In contrast , a five - barreled machine gun firing 1000 rounds per minute fires only 200 rounds per barrel per minute , an acceptable rate of fire for continuous use . The only limiting factor is the rate at which loading and extraction can occur . In a single - barrel design , these tasks must alternate ; a multiple - barrel design allows them to occur simultaneously , using different barrels at different points in the cycle . The design also solves the problem of defective ammunition , which can cause a normal machine gun to malfunction when a cartridge fails to load , fire , or eject from the weapon . As it is powered by an independent source , the gun simply ejects the defective round along with the rest of the cartridges while continuing to operate . M61 Vulcan and other designs . The " M61 Vulcan " 20 mm cannon is the most prolific member of a family of weapons designed by General Electric and currently manufactured by General Dynamics . The M61 is a six - barreled 20mm rotary cannon , which fires at up to 6 , 600 rounds per minute . Similar systems are available in calibers ranging from 5 . 56 mm to 30 mm ( the prototype T249 Vigilante AA platform featured a 37 mm chambering ) . Another multi - barrel design well - known among aviation enthusiasts is the hydraulically driven GAU - 8 Avenger 30 mm cannon , carried on the A - 10 Thunderbolt II ( Warthog ) attack aircraft , a heavily armored close air - support aircraft . It is a seven - barreled cannon designed for tank - killing and is currently the largest bore multi - barrel weapon active in the U . S . arsenal , and heaviest autocannon ever mounted into an aircraft , outweighing the WW II German " Bordkanone " BK 7 , 5 75mm aircraft - mount , tank - killing single barrel autocannon by some 630 kg ( 1 , 389 lb ) , with ammunition . The Gryazev - Shipunov GSh - 6 - 23 and GSh - 6 - 30 are Russian gas - powered rotary cannons with maximum cyclic rates of 9 , 000 to 10 , 000 rounds per minute . Self - driven examples . While electric motors were used to rotate the Vulcan barrels , a few examples of self - operated Gatling - derived weapons use the blow - forward , recoil or gas impulse from their ammunition . The Bangerter machine gun uses a blow - forward operation and is the most complicated machine gun . The Slostin machine gun uses a similar operation but with gas pistons on each barrels . The GShG - 7 . 62 machine gun and GSh - 6 - 23 , both use a more effective , simpler gas piston drive in the centre of the barrel cluster . Minigun . Technically not a " cannon " , the Minigun is more correctly classified as a Gatling - type rotary machine gun . During the Vietnam War , the 7 . 62 mm caliber M134 Minigun was originally created to arm rotary - wing aircraft , and could be fitted to various helicopters as either a crew - served or a remotely operated weapon . With a rate of fire from 2 , 000 to 6 , 000 rounds per minute from a 4 , 000 - round linked belt , the Minigun proved to be one of the most effective non - explosive projectile weapons ever built and is still used in helicopters today . As the GAU - 2B / A , the Minigun was also used on the U . S . Air Force AC - 47 , AC - 119 and Lockheed AC - 130 gunships . The AC - 47 was known during the Vietnam War as " Puff the Magic Dragon " and was said to be " the only thing that scared the VC " . This weapon was also used on selected USAF helicopters . With sophisticated navigation and target identification tools , Miniguns can be used effectively even against concealed targets . The crew ' s ability to concentrate the Gatling ' s fire very tightly produces the appearance of the ' Red Tornado ' from the light of the tracer s , as the gun platform circles a target at night . The most recent development of the M134 ( GAU - 2B / A ) Minigun concept is the Dillon Aero M134D Gatling Gun , a six - barrelled , 7 . 62mm electrically driven machine gun firing at a fixed rate of 3 , 000 rounds per minute , fed from a 3 , 000 - or 4 , 400 - round magazine . The Dillon M134D has been optimized for operational reliability and has an average time between stoppages of 30 , 000 rounds . It is currently in service with U . S . military and NATO forces .