An automatic cannon for a monergole liquid propellant which is designed as a continuously firing drum-type weapon whereby the supply of projectiles, the loading and the dosaging process take place in parallel. The weapon housing of the automatic cannon includes a drum which has a plurality of drum chambers and is disposed in a drum housing so that the drum chambers can be successively rotated into a firing position aligned with the gun barrel. Each drum chamber accommodates a respective projectile chamber and a respective differential piston arrangement for the liquid propellant. The drum is driven in a hybrid manner by a longitudinally displaceable slide, which in turn is driven in one direction by the firing gases supplied through a gas conduction arrangement and in the other direction by a linear electric motor.