Abstract: An externally powered automatic gun or cannon system includes a gun with a pivoting chamber, a shell supply and a shell indexer and a shell rammer for feeding shells from the supply into the gun chamber for firing. Fluid pressure actuators are connected for operating the gun chamber, shell indexer and shell rammer and sensors are provided for sensing extreme operating positions thereof. Timing means are responsive to the sensors for determining lengths of operating times. Electronic control means, responsive to the sensors and timing means, control, on a step-by-step basis, operation of the actuators and firing apparatus according to a pre-established sequence of operational steps causing the automatic loading and firing of the automatic gun.