Supermarine Spitfire PR Mk X

When development of the Merlin 60-series Spitfires began, reconnaissance versions of both the Mk VII and Mk VIII were planned. Seventy aircraft were ordered in April 1942 under the provisional designation PR Mk VIII, but the airframes carrying those serials were eventually completed as Merlin 66-powered LF Mk VIII fighters. A change of policy renamed the pressurised Mk VII-based reconnaissance variant the PR Mk X, and it entered production after — not before — the PR Mk XI.

The PR Mk X married the pressurised Mk VII airframe, with its Lobelle sliding hood and the fighter windscreen complete with bulletproof panel, to the wings and camera installation of the PR Mk XI. The long, thin intake for the pressurisation system ran under the exhaust stacks on the starboard cowling. Performance was much like the PR Mk XI's, but the sealed cockpit mattered where it counted: it allowed pilots to stay above 40,000 ft far longer without the exhausting physiological effects suffered in unpressurised reconnaissance Spitfires.

All sixteen were built during April and May 1944 and the first sortie was flown on 11 May. They served with Nos. 541 and 542 Squadrons on high-altitude reconnaissance for a limited period. The experience gained with them, however, was what justified developing and producing the pressurised PR Mk XIX, the Griffon-engined reconnaissance Spitfire the RAF would keep flying until 1954.