A hypersonic ram jet engine is provided which may be of the hydrogen fueled type and in which static and acceleration thrusts are provided as inherent features of the engine to accelerate the aircraft to speeds at which the ram jet engine can operate efficiently. The static and acceleration thrust is provided by the ram jet engine itself; this being achieved by injecting a secondary airflow into the engine at high pressure by the use of the engine''s liquid hydrogen fuel to condense secondary air, as will be described.