Abstract: A turbojet engine has a capability for propelling an air-borne vehicle over an extremely wide range of operating speeds. A vehicle can be propelled from take-off conditions through speeds in excess of Mach 5. The engine is equipped with a cooling fluid injection system which cools intake air at high operating speeds. Cooling of intake air permits continued turbojet engine operation at speeds which produce stagnation air inlet temperature in excess of those which critical compressor components can tolerate. The inlet air entering the compressor is pre-cooled with injected fluid so that its temperature is reduced below the critical operating temperature limits of the critical compressor components.