Revolver cannons, such as the Mauser MK 213, were developed in World War II by the Germans to provide high-caliber cannons with a reasonable rate of fire and reliability. In contrast to the rotary format, such weapons have a single barrel, and a recoil-operated carriage holding a revolving chamber with typically five chambers. As each round is fired, electrically, the carriage moves back rotating the chamber which also ejects the spent case, indexes the next live round to be fired with the barrel and loads the next round into the chamber. The action is very similar to that of the revolver pistols common in the 19th and 20th centuries, giving this type of weapon its name. A Chain gun is a specific, patented type of Revolver cannon, the name in this case deriving from its driving mechanism.