The Merlin 45 was a simplified version of the Merlin XX. That engine had a two speed supercharger than greatly increased the complexity of the engine. For the Merlin 45 Rolls Royce removed the low-altitude supercharger, producing an engine with the improved higher altitude performance of the Merlin XX but that could fit easily into the fuselage of the Supermarine Spitfire Mk II. The resulting aircraft, the Spitfire Mk V, was originally intended as an interimn aircraft, but went on to be the second most produced variant of the Spitfire.
The Merlin 45 used 100 octane fuel, and a ethylene-glycol pressure cooling system. 3,574 were produced.
1,515 hp at 11,000 feet
1,210 hp with +3lb boost at 18,000 feet
Seafire Mk I
Seafire Mk III
Spitfire PR Mk IV
Spitfire Mk V
Spitfire PR MK VI