Spitfire Mk PR XXI
early 1942 it was evident that Spitfires powered by the new two-stage
supercharged Griffon 61 engine would need a much stronger airframe, in
particular with stiffer wings. The proposed new design was designated the
Mk. 21. However its initial design had a number of flaws that caused
considerable damage to the otherwise excellent Spitfire reputation.
Aside from the more powerful engine the Mk. 21 had several notable features:
In other respects the first production Mk. 21s used the same basic airframe as the Mk. XIV. However the modifications over the Mk. XIV left the aircraft over sensitive to trimming and it exhibited poor performance in trials in late 1944 and early 1945. This led to a damning report from thein which they recommended that, "No further attempts should be made to perpetuate the Spitfire family."
This report caused serious concern for Supermarine as their factory at Castle Bromwich had already been converted to produce Mk. 21s and more were coming off the production lines every day. Luckily the most serious problems were easily solved by changing the gearing to the trim tabs and other subtle control modifications, and the aircraft was cleared for instrument flying and low level flying in trials in March 1945.
It was January 1945 before Spitfire 21s became operational. They had little opportunity to engage the enemy before the war ended, but scored a rare success on 26 April 1945 when two Spitfire Mk. 21s shot up and claimed sunk a German midget submarine which they caught on the surface. With the end of the war most orders for the Mk. 21 were cancelled. Only 120 were completed.