[Llarry]

The rotating-barrel machine gun found applications far beyond aircraft. In particular the 7.62mm variant is used on navy ships, by helicopter door gunners and by army ground forces.

The Vulcan also spawned variant calibers of similar guns. One I've previously discussed is the awesome GAU-8 30mm 7-barrel cannon of the A-10 Warthog. (The photo compares a 30mm GAU-8 round with a .30-06 round.) A variant of the GAU-8 was used by Signaal to develop a 30mm shipboard close-in defense system called Goalkeeper which is used by a number of navies.

A 25mm variant is used by the Marines' AV-8B Harrier as well as some versions of the USAF's AC-130. A lighter 4-barrel version of that designated the GAU-22 is used by the Air Force's F-35A fighter; the Marine and Navy F-35 versions use a gun pod with the same 25mm gun.

To sum up, it appears that the military aircraft gun is here to stay; perhaps only some future development of directed energy will replace it. That would seem to me to be far in the future.