MARCH 1940. N3297 was originally given the standard factory finish as applied to Spitfire Mk Is between late February and mid-May 1940. The underside was painted Aluminium, with the port wing in Night and the starboard wing in White. The cowling was 4in (102mm) longer to accommodate the Rolls-Royce Merlin XX engine. The aircraft was fitted with a three-bladed propeller, various types of which were tested.
MAY 1940. The fin flash and the yellow outer ring of the roundel were applied in response to an Air Ministry directive of May 1, 1940. Yellow undersurfaces for non-operational aircraft had been introduced in late 1939, and instructions of late 1940 specifically included prototype aircraft. Various propellers and spinners were fitted to N3297, including RotoI three- and four-bladed props of 10ft 9in (3-28m) diameter and a Dural de Havilland propeller of 11ft (3-35m) diameter.
OCTOBER 1941. With the cancellation of the Mk III in April 1941, N3297 was sent to Rolls-Royce at Hucknall to become an engine testbed, first flying with a two-stage supercharged Merlin 60 on August 19, 1941. The following month it was fitted with a Merlin 61, these trials aiding the development of the Mk IX. Its markings by this time complied with instructions of August 1940 stipulating underwing roundels of 50in (1-27m) diameter and an instruction of December 1940 specifying 27in (685mm) fin flashes.
The sole Spitfire Mk III, N3297, shortly after its completion, waxed and polished to maximise performance. Note the short-span wings and full doors on the mainwheels.
The most immediately noticeable modification introduced on the Spitfire Mk III was its shorter wing, based on that of the Mk I but “clipped" at rib 19, significantly reducing the type’s wingspan from 36ft 10in (11-2m) to 30ft 6in (9-3m). The new wingtip incorporated a streamlined cover for the navigation lamp. Test pilot Jeffrey Quill voiced concerns that the reduced wing area led to a longer landing run and would make the Spitfire harder to discern from the Messerschmitt Bf 109. A Mk I wing was fitted to N3297 in 1941.