 The Mark 23s, which followed the 21s, were powered by Rolls-Royce Merlin 66 or Merlin 70 engines.The first 26 were built as Mark 21s, followed by 66 Mark 23s; the first 14 Mark 21s were converted to fighter-reconnaissance aircraft, with two F24 cameras in both vertical and oblique positions in the rear fuselage, above and behind the radiator fairing; the designation of these modified Mustangs was changed from Mark 21 to Mark 22.An additional 14 purpose-built Mark 22s, built after the Mark 23s, and powered by either Packard V-1650-7s or Merlin 68s, completed the production run.