tail surfaces, similar to those of the Supermarine Spiteful. A total of 287 Mk 22s were built: 260 at Castle Bromwich and 27 by Supermarine at South Marston. The Mk 22 was used by only one regular RAF unit, 73 Squadron based on Malta. However 12 squadrons of the Royal Auxiliary Air Force used the variant and continued to do so until March 1951. The Mk 22 was also used at Flying refresher schools. In May 1955 the remaining F.22s were declared obsolete for all RAF purposes and many were sold back to Vickers-Armstrongs for refurbishment and were then sold to the Southern Rhodesian, Egyptian and Syrian Air Forces."Spitfire F.22." Air-Britain Aeromiltaria, Issue 2, 1991, pp. 39–46. Mk 23 (type 372) The Mk 23 was to be a Mk 22 incorporating a revised wing design which featured an increase in incidence, lifting the leading edge by . It was hoped that this would improve the pilot's view over the nose in flight and increase the high speed and dive performance of the aircraft. The modified, hand-built wing was first fitted to a Mk VIII JG204 which was tested from July 1944. However the tests were disappointing and, after discussions at Supermarine, it was decided to build a new prototype using the Mk 21 prototype PP139: in this form the prototype was designated F Mk 23, and was to be renamed the Supermarine Valiant'''. However the new wing gave less than perfect handling characteristics and so the Mk 23 was never built from the Mk 22 airframe as intended. Mk 24 (type 356) The final Spitfire variant, the Mk 24, was similar to the Mk 22 except that it had an increased fuel capacity over its predecessors, with two fuel tanks of 33 gal (150 L) each installed in the rear fuselage. There were also zero-point fittings for rocket projectiles under the wings. All had the larger "Spiteful" tail units; modifications were also made to the trim tab gearings to perfect the F Mk 24's handling. The F Mk 24 achieved a maximum speed of and could reach an altitude of in eight minutes, putting it on a par with the most advanced piston-engined fighters of the era. Although designed as a fighter-interceptor aircraft, the Spitfire proved its versatility in other roles. As a fighter, the F Mk 24 armament consisted of 4 × 20 mm Hispano cannon – operational experience