Although the Griffon was designed for naval aircraft, on 8 November 1939 N E Rowe of the Air Ministry suggested fitting the Griffon in a Spitfire. Three weeks later permission was given to Supermarine to explore the possibilities of adapting the Griffon to the Spitfire; in response Supermarine issued 'Specification 466' on 4 December. This decision led to a change in the disposition of the engine accessories to reduce the frontal area of the engine as much as possible.[5] As a result the frontal area of the bare Griffon engine was 7.9 square feet (0.73 m2) compared with 7.5 square feet (0.70 m2) of the Merlin, despite the Griffon's much larger capacity.[6] This redesigned engine first ran on 26 June 1940 and went into production as the Griffon II.