M61 Vulcan (autocannon)

One of the first electrically-powered, rotating-barrel machine guns, firing 7.62mm ammunition, the M61 Vulcan was introduced for armed helicopters and AC-47 ground attack aircraft in the Vietnam War. It has six barrels but one actual firing chamber, the barrels being turned by an electric motor.

Turning the barrels allows them more time to cool, and also allows the ammunition and loading mechanisms to be separated from the firing mechanism. These allow for firing rates of 4000 or 6000 bullets per minute, far greater than conventional machine guns.

While it worked well, it is being replaced by the lighter, cheaper and more reliable M134, or, when a more powerful round is needed, the 25mm M242 Bushmaster.