Short answers, pulled from the story.
The M61 Vulcan is a six-barrel, 20 mm Gatling-style rotary cannon that fires at rates typically around 6,000 rounds per minute. It has served as the principal cannon armament of United States fixed-wing military aircraft for over forty years.
General Electric designed the M61 Vulcan in 1946 under a program called Project Vulcan. General Dynamics manufactures it today, after ownership passed from General Electric's aerospace division, sold in 1993, through Martin Marietta and Lockheed Martin Armament Systems.
The M61 Vulcan was first used in aerial combat on the 4th of April 1965, when North Vietnamese MiG-17s attacked F-100 Super Sabres escorting Vulcan-armed F-105 Thunderchiefs. The first confirmed Vulcan gun kill followed on the 29th of June 1966, when Major Fred Tracy downed a MiG-17.
The M61 Vulcan typically fires 6,000 rounds of 20 mm ammunition per minute, roughly 100 rounds per second. The lighter M61A2 variant, built with thinner barrels for the F-22 Raptor, can reach up to 6,600 rounds per minute.
The M61 Vulcan arms fighters including the F-14 Tomcat, F-15 Eagle, F-16 Fighting Falcon, F/A-18 Hornet, F-22 Raptor, F-4 Phantom II, and F-104 Starfighter. It has also been fitted to the F-106 Delta Dart, F-111 Aardvark, AC-130 gunships, and the B-52H and B-58 bombers, and its mechanism underlies the Navy's Mk 15 Phalanx and the M163 Vulcan Air Defense System.
The M61 Vulcan was developed because jet-powered fighters needed a far higher rate of fire than existing aircraft guns could deliver to score hits at high speed. The Army issued General Electric a contract for Project Vulcan in 1946 after captured German cannon designs showed both the promise and the limits of a single-barrel revolver cannon.