An air-breathing turbojet engine (101) for a hypersonic vehicle is shown. The engine comprises a pump for pumping a cryogenic fuel, an inlet (102) configured to compress inlet air by one or more shocks, a cooler (103) to cool the compressed inlet air using the cryogenic fuel, and a turbo-compressor (104) to compress the air further. A combustor (105) receives compressed cooled air from the turbo-compressor and a first portion of the cryogenic fuel for combustion. A first turbine (106) expands and is driven by combustion products, and a second turbine (107) expands and is driven by a second portion of the cryogenic fuel. The first turbine and the second turbine drive the turbo-compressor via a shaft. An afterburner (109) receives combustion products from the first turbine and the second portion of the cryogenic fuel from the second turbine for combustion therein.