Quick removal of the barrel is a feature of a sub-machine gun, the invention of an Australian soldier, which has become an important weapon in arming men of the British Empire. After firing 300 rounds, the hot barrel of the 10 1/2-pound gun must be replaced, and its simple mechanism makes it possible to complete the change in a few seconds at the touch of a button. The gun is said to be extremely deadly, too, having a greater velocity and deeper penetration, with lighter recoil.