MIL-DTL-45500-1 Gun, Automatic, 20Mm: M61 And M61A1This specification sheet covers a type of six-barrel, electrically fired, 20 millimeter \(mm\) automatic guns M61 and M61A1. The gun utilizes an ammunition feeder and is power driven through its cycle of operation by either an electric or hydraulic drive, or ram air turbine for installation in an aircraft armament pod system.