T^HE simplest form of liquid-fuel jet engine for high-speed short-range missiles is the so-called one-shot system, in which the fuel and propellant are contained in tanks capable of standing the combustion-chamber pressure, and are forced into the combustion chamber by the pressure on an inert gas. Compactness and lightness are essential features of its design, and in certain uses quick starting and reliability are also essential. The employment of a separate inert gas from a high-pressure tank adds weight and complications to such a rocket, and lessens its reliability in uses requiring storage. The tank must contain an amount of gas which when expanded to combustion-chamber pressure will fill both propellant tanks. It must be strong enough to hold that pressure in a substantially smaller volume. Regulator valves are necessary to reduce the gas pressure to the pressure needed. The whole system is subject to leaks, and may not be in working order when needed. Another consideration in the design of such missiles is the speed with which they can be launched. At present this depends on the method employed for initially energizing the propulsion jet, and this in turn depends largely upon the kind of combustible agents employed. But whether the agents used are self-igniting when admitted to the combustion chamber, or are such as must be ignited by special means, there still is an appreciable time which must pass before the motor develops its full thrust. It is desirable to reduce this time lag as much as possible.