The Rolls-Royce Crecy was a British experimental two-stroke, 90-degree, V12, liquid-cooled aero-engine of 1,593.4 cu.in (26.11 L) capacity, featuring sleeve valves and direct petrol injection.

Sir Henry Tizard, Chairman of the Aeronautical Research Committee (ARC), was a proponent of a high-powered "sprint" engine for fighter aircraft and had foreseen the need for such a powerplant as early as 1935 with the threat of German air power looming.

"The Chairman remarked that if it was the desire of the Air Ministry to develop a type of sprint engine for home defence....there was the question as to how far fuel consumption could be disregarded.

Mr Ricardo had raised this point in a recent conversation by enquiring whether a high fuel consumption might not be permissible under certain circumstances, for if so, an investigation of the possibilities of the two-stroke petrol engine appeared to be attractive.

"Previous experience gained between 1927 and 1930 using two converted Rolls-Royce Kestrel engines through an Air Ministry contract had proven the worth of further research into a two-stroke sleeve-valved design.

By the time they started development of the Crecy itself, in conjunction with the Ricardo company, the decision had been taken by the Air Ministry to revert to a more conventional spark-ignition layout, although still retaining fuel injection.

[6] The thrust produced by the exceptionally loud two-stroke exhaust was estimated as being equivalent to a 30% increase in power at the propeller on top of the rated output of the engine.

Stratified charge was used: the fuel was injected into a bulb-like extension of the combustion chamber where the twin spark plugs ignited the rich mixture.

The rich mixture maintained near the spark plugs reduced detonation, allowing higher compression ratios or supercharger boost.

[13] In the summer of 1941, Supermarine Spitfire Mk II P7674 was delivered to Hucknall and fitted with a Crecy mock-up to enable cowling drawings and system details to be designed.

It was planned for the first production Spitfire Mk III to be delivered to Hucknall in early 1942 for fitting of an airworthy Crecy, but this never took place.

The report stated that the Crecy's maximum power output would be too much for the Spitfire airframe but that a derated version would have considerable performance gains over the Griffon-powered fighter.

[16] From 1943 a number of postwar transport projects were considered, taking advantage of the Crecy's unique characteristics for land, sea and air applications.