Supermarine Spitfire Mk VII

The Mk VII repeated the Mk VI idea — a pressurised Spitfire for very high altitude — but with the right engine. The Merlin 64 and 71, with two-stage, two-speed superchargers and an intercooler, delivered power up high that the single-stage Mk VI simply could not. The cabin was pressurised in much the same way, by a Marshall compressor on the right of the engine fed through a long intake under the starboard exhaust stubs, an automatic valve holding a maximum differential of two pounds per square inch from about 28,000 ft upwards. The change pilots welcomed most was the hood: instead of the Mk VI's clamped-down canopy, later Mk VIIs had a double-glazed Lobelle hood that slid back like any other Spitfire's, sealing against the fuselage with rubber tubing.

Together with the Mk VIII, the Mk VII introduced the structural package that defined every two-stage Merlin Spitfire: revised internal structure, ailerons shortened by 8.5 inches to cure the flutter blamed for break-ups in steep dives, a nose seven inches longer, split radiators with the intercooler matrix alongside the main unit, and undercarriage legs with forward-facing torque links and slightly concave doors that let the wheels sit lower and freed the upper wing of its blisters. Internal fuel rose to 122 gal, nearly half as much again as earlier marks, with extra tanks in each wing leading edge. Extended tips took the span to 12.2 m, though with the high-altitude threat never materialising many aircraft later reverted to standard tips.

Of the 140 built, most used the Merlin 64 (F Mk VII) or the Merlin 71 (HF Mk VII), the latter with a Bendix-Stromberg anti-g carburettor. The HF was superb high up, with a service ceiling of 45,100 ft — 13,700 m. The French ace Pierre Clostermann recorded in his memoirs the interception of a long-range reconnaissance Messerschmitt Bf 109G at 40,000 ft by a "Strato Spitfire" of No. 602 Squadron over Scapa Flow in early 1944.

The National Air and Space Museum keeps an HF Mk VIIc with a 1,565 hp Merlin 61 that never saw combat. Shipped from the factory in March 1943 to a maintenance unit at Sealand, it was dismantled and sent to the United States, received by the Army Air Force in May 1943, used for evaluation and transferred to the museum in 1949. Its recorded dimensions — 9.12 m long, 3.02 m high — are those of a Mk VII with conventional wingtips.