A gas compressor is provided which can be utilized in a jet engine for propulsion of a flight vehicle at velocities ranging from static to very high Mach numbers. The jet engine includes a housing with an inlet, a mixing chamber in fluid communication with the inlet, a diffuser section in fluid communication with the mixing chamber, a combustion chamber in fluid communication with the diffuser section and an outlet in communication with the combustion chamber. Auxiliary gas injection nozzles located downstream of the mixing chamber direct a high velocity gas stream toward the outlet to induce a region of sufficiently low pressure within the mixing chamber to cause a supersonic flow of gas from the inlet section through the mixing chamber. Cryogenic fuel is injected into the mixing chamber to modify the stagnation enthalpy, pressure and temperature of the supersonic flow therethrough. Fuel is injected into the combustion chamber where the mixture of the compressed air flow from the diffuser and the fuel is ignited to produce thrust. The outlet is adjustable to provide the amount of back pressure required in the combustion chamber for stable operation.