The Gatlin gun's multiple rotating barrel arrangement was revived in the 1950s to create the 20mm Vulcan cannon, first used in fighters like the F-104. There simply wasn't any way to get super high rates of fire out of a single barrel weapon at the time. Earlier planes like the F-100 mounted 4 20mm cannons, each firing at about 1,200 rounds per minute. A single M61 Vulcan was a lighter and simplier installation with an even higher rate of fire. After a second or so to spin up, Vulcan can fire up to 6,000 rounds per minute. Inertia is a factor - a half second burst might fire 25 rounds or so, with the rate quickly increasing to 100 rounds per second.

Later, a 7.62mm version called the minigun was created for use in Viet Nam. It could also fire up to 6,000 rounds per minute, although it was sometimes slowed down to lower rates of fire. A 30mm version was created for the A-10 Warthog, featuring a rate of fire of something like 2,000 to 4,000 rounds per minute. That's a lot of firepower, especially when firing depleted uranium rounds. Even a half second burst can rip any armored vehicle to sheds. These have proven extremely effective weapons. I've read of an experimental 5.56mm version that was developed but never fieled in the 1960s. Reportedly, it could fire up to 10,000 rounds per minute.