A photo of a 20mm Vulcan automatic cannon. It has six barrels and can fire up to 7200 rounds per minute. It was invented in the 1800s by American Richard J. Gatling and is used on most U.S. military surface ships. Consists of a rotating cluster of gun barrels each of which is fired once by its own bolt once every complete revolution of the barrel cluster. The gun bolts are attached to the motor which rotates the barrel cluster and then are captured in tracks running fore and aft. This specific gun can be found in Washington D.C., U.S.A.