Way back, in 1862, someone dr. Gatling of USA patented a manually operated, multi-barreled mechanical "machine gun", one
of the most successful of such designs. Being gradually updated, this weapon, in many versions, served with number of armies around the world as an infantry support or a light artillery weapon. Usually chambered for the contemporary general issue rifle cartridge, the XIX century Gatling guns usually have 6 to 10 barrels, mounted around the single axis. Some naval Gatlings, thought, have had calibers up to 1 inch (25mm), and some derivatives, like the Hotchkiss, were up to 53mm in caliber. When crank at the back of the gun was rotated, the "bundle" of barrels rotated too. Each barrel had its own bolt, which completed full reloading circle per one turn of the barrels bundle. This resulted in the rate of fire as high as 200+ rounds per minute - quite an achievement in the era of the single-shot and even magazine fed rifles. While first successful "true" machine guns appeared by 1890, some Gatling guns seen use until World War 1, especially with the navies. As the automatically operated machine guns became more and more mature, Gatling guns were gradually forgotten, until the late 1940s. At that time, the speed of combat aircrafts became so high, so even most fast-firing conventional machine guns became too slow to achieve desirable number of hits during the very brief encounters. This spawned the famous "Project Vulcan", that was intended to develop a super-rapid firing weapon for US Air Forces. Project was handled by the General Electric Co. First tests were conducted with the late 19th century Gatlings, fitted with electrical drive instead of manually operated crank; this immediately resulted in the rate of fire of about 4 000 rounds per minute, which was very impressive (it must be noted, that such tests were first conducted in early 1890s, but lead to no practical results at that time - there were no need in the rate of fire of up to 3 000 RpM). Further development resulted in some experimental, electrically driven, .60 caliber machine guns with 6 barrels, and, in 1956, the 6-barreled 20mm T171 gun was officially adopted as the M61 aircraft gun. This gun could fire at the rate of 4 to 6 thousands rounds per minute. This achievement is possible due to the fact that gun has multiple barrels, and the rate of fire per one barrel is about 1 000 rounds per minute or even less, allowing them to not to overheat. M61 became the main aircraft gun for US AF, and also was used on M161 and M163 Vulcan ground anti-aircraft gun mounts. The navies also turned back to Gatlings with the Vulcan-Phalanx CIWS (Close-In Weapon System).