[Llarry]

The 20mm GE M61 Vulcan aircraft cannon was a winner. It was not universally adopted, however. Both the USAF F-106 interceptor and the F-111 strike aircraft had no guns, though both could be fitted with an optional Vulcan if needed. The Air Force bought the Navy A-7 attack aircraft and, like the Navy, fitted its A-7D with a Vulcan. The Navy's A-6 Intruder medium attack aircraft also had no guns. The older A-1 Skyraider that was used so effectively in Vietnam had the older four M3 20mm cannon installation.

Vietnam brought a huge number of variations on the rotating-barrel aircraft gun. One of the earliest was the 7.62mm variant used by the AC-47 gunship. The U.S. Army also adapted the 7.62 aircraft gun to ground use.

Post-Vietnam brought other variants. The Marine Corps bought UK-built Harriers with cannon pods. The AC-47 and other gunships used so effectively in Vietnam were succeeded by the Air Force AC-130 with more sophisticated sensors and heavier armament, including a 105mm howitzer.

The Vulcan and its variants did not escape the notice of the Army and the Navy surface force, either. Both services adopted the 20mm as an air defense weapon; the Army mounted the Vulcan on an armored personnel carrier and the Navy gave a large variety of ships multiple guns to provide last-ditch defense against missile attacks.
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