Rolls-Royce R engine was invaluable in the subsequent development of the Rolls-Royce Merlin engine and the Spitfire. A de-rated R engine, known as the Griffon, was tested in 1933, but it was not directly related to the production Rolls-Royce Griffon of 1939, of the same exact bore/stroke and resultant displacement figures as the "R" design. Three examples of the R engine are on public display in British museums as of 2014. Rolls-Royce realised that the Napier Lion engine used in the 1927 Supermarine S.5 Schneider Trophy winner had reached the peak of its development, and that for Britain's entrant in the next
Rolls-Royce Crecy fighter. Studies on the de Havilland Mosquito also showed it to raise complex problems with Crecy installation. In 1942 Rolls-Royce Hucknall received a North American P-51 Mustang for engine installation trials. This prompted a series of studies for a Crecy version and the Mustang turned out a more suitable mount than the Spitfire. However these studies were not taken further. As the possibility of a flight-worthy engine approached, on 28 March 1943 Hawker Henley "L3385" was delivered to Hucknall for fitting with a Crecy. However the engine never became available and the aircraft remained at Hucknall until when it was