The Vulcan M61 hydraulic electric air cannon is considered one of the most powerful guns relied on by the U.S. military due to its impressive strength and speed. The Vulcan M61 operates with six barrels, is air-cooled, and functions electrically similar to the Gatling gun, firing 20mm rounds at an extremely high rate, reaching up to 6,000 rounds per minute. The Vulcan was first used in April 1965 in Vietnam on the F-105 Thunderchief aircraft and has been utilized with the U.S. Air Force's F-15, F-16, F-22, as well as the F-14 and F/A-18 aircraft. The Vulcan M61 gun has also been installed in side-firing gun mounts on the Fairchild AC-130 and Lockheed AC-130 military aircraft.