This Mustang, AM208, exchanged its Allison V-1710 for a Merlin and was first flown with this engine in October 1942.

Early production Spitfires during final assembly at Eastleigh in January 1939. Note the Rolls-Royce Merlin engines in the foreground.

The Spitfire III N3297 in October 1941, with standard wing tips and a Merlin 60 series engine (note the twin wing radiators) and four-bladed propeller. As a Rolls-Royce test-bed, this was effectively a Spitfire IX prototype.
Spitfire N3297 was the only Mk III built. It was used as a development aircraft and was fitted for a while with the Merlin 61. To absorb the additional power a large four-bladed propeller was fitted.

PETER R.WESTACOTT'S painting, Borrowed Sky, depicting a Spitfire Vb on No 303 (Polish) Sqn patrolling the English Channel in 1942.

An evocative shot of D.H.103 Hornet PX225 with inward rotating Merlin 130 (starboard) and Merlin 131 (port) capable of 4,140 h.p. between them