The pre-production Griffon I shared the R engine's bore and stroke, but was otherwise a completely new design that first ran in the Experimental Department in November 1939. Although this single engine was never flown, the production version, the Griffon II, first flew in 1941 installed in the Fairey Firefly. A significant difference between the R and the production Griffon was the re-location of the camshaft and supercharger drives to the front of the engine to reduce overall length. Another length-reducing measure was the use of a single magneto (the R had two, mounted at the rear), this again was moved to the front of the engine.