Similar to tiltrotor concept, but with turbojet or turbofan engines instead of ones with propellers. The turbofan is quieter and has better range-specific fuel consumption than the turbojet. The "Vampire" was powered by a single Bristol-Siddeley Orpheus afterburning turbojet engine producing of thrust. The first General Electric turbofan was the aft-fan CJ805-23, based on the CJ805-3 turbojet. There are still further subdivisions for piston-engined, turbojet, turboprop, and rocket-engined aircraft. The airframe appeared ideally suited to test turbojet propulsion. The powerplant was to be General Electric's new TG-180 turbojet engine. Early U-2 variants were powered by Pratt & Whitney J57 turbojet engines. Thrust was provided by a pair of axial flow Rolls-Royce Avon turbojet engines. A turbojet train is a train powered by turbojet engines. ATREX was superseded by the Preecooled Turbojet (PCTJ) and Hypersonic Turbojet studies. Main engine a SNECMA TF-104 turbojet. The Comet 1 featured de Havilland Ghost 50 Mk1 turbojet engines. The Crusader was powered by a Pratt and Whitney J57 turbojet engine. France in a Sud-Ouest Trident II mixed power (turbojet & rocket engine) aircraft.