This was essentially a low altitude, unpressurized MkVII, with a 1565 HP Merlin 61 or a 1710 HP Merlin 63 driving a 4-bladed airscrew. Changes to the carburetor allowed negative "g" manoeuvering. Although the MkVIII was intended as the major developmental line for the Spitfire, the MkIX was hurried into service, and only 1652 were eventually produced, many modified for tropical climates. A single airframe was converted into the first official 2-seat Spitfire -the Tr8- but no great interest was shown and it was not followed up.