The Rolls-Royce/Snecma Olympus 593 was an Anglo-French turbojet with reheat (afterburners), which powered the supersonic airliner Concorde. It was initially a joint project between Bristol Siddeley Engines Limited (BSEL) and Snecma, derived from the Bristol Siddeley Olympus 22R engine. Rolls-Royce Limited acquired BSEL in 1966 during development of the engine, making BSEL the Bristol Engine Division of Rolls-Royce. Until regular commercial flights by Concorde ceased, in October 2003, the Olympus turbojet was unique in aviation as the only turbojet with reheat powering a commercial aircraft. The overall thermal efficiency of the engine in supersonic cruising flight (supercruise) was about 43%, which at the time was the highest figure recorded for any normal thermodynamic machine. Development The initial design of the engine was a civil version of the Olympus 22R, redesignated as the 591. The 22R had been designed for sustained (45 minutes) flight at Mach 2.2 as the engine for the BAC TSR-2. The 591 was redesigned, being known as the 593, with specification finalised on 1 January 1964. Bristol Siddeley of the UK and Snecma Moteurs of France were to share the project. SNECMA and Bristol Siddeley were also involved in an unrelated joint project, the M45H turbofan. The early development stages validated the basic design concept, but many studies were required to meet the specifications which included fuel consumption (SFC), engine pressure ratio, weight/size and turbine entry temperature. Initial studies looked at turbojets and turbofans, but the lower frontal cross-sectional area of turbojets in the end was shown to be a critical factor in achieving superior performance. The competing Russian Tu-144 initially used a turbofan with reheat, but changed to a turbojet without reheat with considerable improvement in performance. Development of the engine and engine accessories was the responsibility of Bristol Siddeley, while BAC was responsible for the variable intake and overall engine installation, and Snecma the exhaust nozzle/thrust reverser/noise attenuation and the afterburner. Britain was to have a larger share in production of the Olympus 593 as France had a larger share in fuselage production. Ground test running of the engines was co-ordinated between Bristol Siddeley, Patchway; the National Gas Turbine Establishment (NGTE), Pystock, UK; and the Centre d'Essais des Propulseurs (CEPr) at Saclay, France. Increases in aircraft weight during the design phase led to a take-off thrust requirement which could not be met by the engine. The required shortfall of 20% was met with the introduction