Supermarine Spitfire Mk VII AB450 protototype
The Mk VII was developed as an advanced version of the pressurized Mk VI, incorporating more power and pilot-friendly modifications. Supermarine anticipated that the Mk VII would replace the Mk V, which was originally considered an interim model, and would be mass-produced. The F and HF Mk VII models were equipped with the two-speed two-stage Merlin 60 and 70 series engines, which represented a significant advancement for the Spitfire. The Mk VI’s extended wingtips and retractable tail wheel were retained, and small fuel tanks were added to the leading edge of each wing for the first time. The new engine required a longer nose, resulting in a larger rudder and trim tab and a longer, stronger fuselage. The F Mk VII was powered by either a Merlin 61, which produced 1,300 horsepower at 23,000 feet (7,010 meters), or a Merlin 64, which produced 1,450 horsepower at 21,000 feet (6,401 meters). Both engines were equipped with a two-stage supercharger for improved performance at high altitude, and air scoops were fitted under each wing. The HF Mk VII was equipped with a Merlin 71 engine with a Bendix “anti-g” injection carburetor. The Mk VII was fitted with a more suitable “Lobelle” double-glazed sliding cockpit canopy, replacing the previous bolting solution, and a more advanced version of the Marshall compressor was used for cockpit pressurization. The first Mk VII prototype, AB450, flew in June 1942, and the first examples entered RAF service with the High Altitude Flight at Northolt in September of that year. Operational units began receiving the Mk VII in March 1943, with 124 Squadron at North Weald being the first to operate them. The Mk VII was flown by several squadrons, including 118, 131, 154, 313, 518, 519, 611, and 616. Despite its improvements, the Mk VII was only slightly more successful than its predecessor, and it was eventually superseded by the Mk IX as the premier high-altitude Spitfire. A total of 164 Mk VIIs were produced, starting with a single prototype, AB450, followed by three production batches in the serial ranges BS121, BS142, BS229, BS253, BS427, EN178-EN512, and MB761-MD190, which were built between August 1942 and early 1944.