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 worked on the Fokker-Leimberger, an externally powered 12-barrel Gatling gun that could fire more than 7,200 7.92×57mm 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 MG 151 and 30mm MK 108 cannon used 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