Supermarine Spitfire PR Mk XI

The PR Mk XI descended from no single version but borrowed from the Mk VII, VIII and IX. It was meant to use the Mk VIII airframe, but delays to that series meant it was built on the Mk IX instead. It was recognisable by a deeper nose fairing housing a 14.5 gal oil tank and by the unarmoured wrap-around windscreen typical of reconnaissance aircraft. Booster pumps for the wing tanks sat under teardrop fairings, a retractable tailwheel was standard, and most aircraft carried the large-area pointed rudder.

It was the first reconnaissance variant able to carry two vertical F52 cameras with 36-inch focal length lenses in the fuselage behind the cockpit, though other fits were available: vertical F24s with 14-inch lenses plus an oblique 8-inch camera facing to port, or extra cameras in underwing fairings for tactical work. Of the 471 built, 260 had Merlin 61, 63 or 63A engines and the remaining 211 the high-altitude Merlin 70; nearly all carried the Aero-Vee dust filter in the extended carburettor intake under the nose.

With no guns and no armour, the PR Mk XI relied on speed and altitude: 671 km/h at 24,000 ft, cruising at 636 km/h at 32,000 ft, with the ability to climb to 44,000 ft in an emergency. The cockpit was not pressurised, so that last resort carried a physiological price no pilot could pay for long. Slipper tanks of 30, 45, 90 and even 170 gal could be hung under the centre section.

In 1943, with the new reconnaissance Spitfire delayed, the Air Ministry proposed converting all PR units to the De Havilland Mosquito; the Air Staff accepted that Mosquitoes could fly 90 per cent of the missions. Air Vice Marshal John Slessor of Coastal Command countered that the Spitfire was smaller, used half as many Merlins and was faster, more manoeuvrable and quieter, so production should be increased rather than cut. He won: PR Mk XI output was accelerated at the expense of fighters. The first were built in November 1942 and the last in December 1944, when the PR Mk XIX took over.