The Army used the 20mm round 6 barrel version because I had four of them in my platoon as a young 2nd LT. The Army also adopted what we called the mini gun, the smaller version strapped to helicopters using either 5.56 or 7.62. The Vulcan came in self propelled and towed versions, both now sitting in museums now.
“The Army used the 20mm round 6 barrel version...I had four of them in my platoon as a young 2nd LT...also adopted what we called the mini gun, the smaller version strapped to helicopters using either 5.56 or 7.62. The Vulcan came in self propelled and towed versions, both now sitting in museums now.” [Midwesterner53, post 39]
As a cadet at the US Air Force Academy in the early 1970s, I recall Army personnel bringing in a number of weapon systems to augment our field training sessions, for display & education. One was a towed version of the Vulcan gun. It was a high point of a cadet career; I can still recall sitting in the gunner’s seat, manipulating the controls while an NCO explained operation and function for my benefit.
Gun systems have been giving way to missile systems in air defense applications for decades. Individual missile rounds may cost more per shot than gun rounds, but the total missile package (sensors, launchers, fire control, mounting hardware etc) is lighter, boasts longer range, and provides a higher kill probability than any gun.