Abstract: A liquid propellant gun system which operates by the direct injection of a two-component hypergolic liquid propellant, i.e., a liquid oxidizer and a liquid fuel, into the combustion chamber in the gun to the rear of the projectile to be propelled. The preferred embodiment is an adaption of the inventive gun system for use as a rapid fire, small caliber, high muzzle velocity aircraft cannon system. As the hypergolic components come into contact and burn, the projectile is propelled forwardly through and out of the gun barrel by the resultant combustion gases. Unlike the prior art, the inventive system permits a significantly higher rate of fire of projectiles, eliminates the need for an igniter, prevents misfires and detonations, materially increases the reliability of the gun and the system thereof, and greatly reduces both the weight and the volume needed to house and to use the gun and the other components of the system.