Supermarine Spitfire Mk. III

The Supermarine Spitfire Mk. III was the first redesign of the basic Spitfire, introducing several improvements such as a retractable tail wheel, full undercarriage covers, internal bulletproof windscreen and a strengthened undercarriage. It was to be powered by a Rolls-Royce RM 2SM, later known as the Merlin XX, developing 1,390 hp.

It was decided that the Merlin XX was to be prioritised for the Hurricane Mk II, so the Spitfire Mk III was passed over and production centred on the Mk V instead. The two prototypes were used for development at Supermarine and Rolls Royce.