airframe as the Mk XIV. The first true Mk 21 prototype, PP139 first flew in July 1943, with the first production aircraft LA187 flying on 15 March 1944. The modifications over the Mk XIV made the Mk 21 sensitive to trim changes. LA201s poor flight control qualities during trials in late 1944 and early 1945, led to a damning report from the Air Fighting Development Unit Supermarine were seriously concerned because Castle Bromwich had been converted to produce Mk 21s and more were coming off the production lines daily. Jeffrey Quill commented that, After intensive test flying, the most serious problems were solved by changing the gearing to the trim tabs and other subtle control modifications, such that the Mk 21 was cleared for instrument flying and low level flight during trials in March 1945. An AFDU report on LA215 issued that month noted that the Spitfire 21 was now much easier to fly, General Handling The modifications carried out to this aircraft have resulted in an improvement of the general handling characteristics at all heights ... Conclusions The critical trimming characteristics reported on the production Spitfire 21 have been largely eliminated by the modifications carried out to this aircraft. Its handling qualities have benefitted (sic) to a corresponding extent and it is now considered suitable both for instrument flying and low flying. It is considered that the modifications to the Spitfire 21 make it a satisfactory combat aircraft for the average pilot. Spitfire 21s became operational on 91 Squadron in January 1945. The squadron had little opportunity to engage the Luftwaffe before the war ended but scored a rare success on 26 April 1945, when two Spitfire Mk 21s shot up and claimed to have 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 and only 120 were completed. In 1946 forty Spitfire 21s were delivered to Shoeburyness; once there their leading edges were removed and destroyed in "lethality" tests. Some aircraft had less than five hours flying time. Mk 22 (type 356) The Mk 22 was identical to the Mk 21 in all respects except for the cut-back rear fuselage, with the tear-drop canopy, and a more powerful 24 volt electrical system in place of the 12 volt system of all earlier Spitfires. Most of the Mk 22s were built with enlarged