Vickers Supermarine
Spitfire Mk XX

Only two handful of aircraft were ever designated Mk. XX and they were both prototypes for other marks. The first was DP 845. Initially a Mk. IV, it was re-designated a Mk. XX shortly after its maiden flight on 27 November 1941  and was later refitted to be the prototype Mk. XII. The Mk. IV designation was taken over by the PR Type D.

The second Mk. 20, DP 851, initially had a Griffon II engine and made its first flight in August 1942. In December  it was refitted with a Griffon 61 and re-designated as a Mk. 21 initial prototype.