During 1941 work began on adapting the Spitfire to use the new Merlin 61 engine. This had a two-stage supercharger, which improved its performance at high altitude by around 50%. The new engine was fitted to Spitfire N3297 (the only Mk III Spitfire), and the modified aircraft first flew on 27 September 1941. The timing was perfect. September 1941 also saw the operational debut of the Fw 190. The new German fighter outclassed the Spitfire V, then the RAF’s best front line fighter. Tests early in 1942 proved that the Merlin 61 powered Spitfire was the answer – it reached a maximum speed of 414 mph at 27,200 feet and could still reach 354 mph at 40,000 feet.
Work began on redesigning the Spitfire airframe to take the new heavier more powerful engine. This work would produce the pressurised Mk VII and the unpressurised Mk VIII Spitfires. These aircraft were expected to be the answer to the Fw 190. In the event the interim Mk IX performed that function. This version used a Mk V fuselage with as few changes as possible, and entered front line service in July 1942, nearly a year before the Mk VIII.
The Mk VIII (and VII) featured a strengthened fuselage with a retractable tail wheel. Each wing carried a 14-gallon self sealing fuel tank, and the main fuselage fuel tank was increased in size to 96 gallons. These changes gave the Mk VIII the same range as the Mk V, although as this distance was achieved at a higher speed, the Mk VIII could stay in the air for less time than the Mk V. Most Mk VIIIs used a new broad-chord, or pointed-tip rudder. It also featured a new tropical filter – the Vokes Aero-Vee – that was so well designed it was installed on all Mk VIIIs and adapted for tme Mk IX. The Mk VIII used the “c” wing armament (four cannon or two cannon and two machine guns) and could carry up to 1,000lbs of bombs.
A Mk VIII was the first Spitfire to use the revised cockpit seen on most later models, with a cut-down rear fuselage and a bubble canopy. This design improved the rearwards visibility of the aircraft, and was used in late production Mk IXs, the very similar Mk XVI and the late Mk 20 and above.
1,657 Mk VIIIs were produced in all, so although it never replaced the Mx IX in Britain and Northern Europe it was still a major version of the Spitfire. It was produced in three versions. The F.VIII using the 1,560 hp Merlin 61 was the standard fighter model. The HF.VIII used a 1,655hp Merlin 70 and was a high altitude fighter and the LF.VIII used the 1,705 hp Merlin 66 and was officially a low altitude fighter, although its best altitude was not that much lower than for the F.
The success of the Mk IX reduced the importance of the Mk VIII. Although the first production model was completed in November 1942, it took until June 1943 for the first squadron to be equipped with the model. One reason for the delay was that it had been decided to use the Mk VIII in the Mediterranean and Far East, and so the first squadron to use it was No. 145, based on Malta. By the summer of 1943 the crisis in the Mediterranean was in the past, and the Mk VIII saw most of its service during the invasion of Italy, often in a ground attack role.
The Mk VIII arrived in the Far East towards the end of 1943. This was just in time, for at the start of 1944 the Japanese launched their Arakan offensive. The Mk V Spitfire had been on a par with the best Japanese fighter in Burma, the Ki 44 “Tojo”, but the Mk VIII was much faster. The Japanese Army Air Force was soon driven from the skies over the Arakan, allowing the Allies to keep their isolated troops supplied from the air. The same pattern was repeated in March 1944 when the Allied air forces in India were able to keep 55,000 troops supplies at Kohima and Imphal.
Finally, the Mk VIII was used by the Royal Australian Air Force, at first for the defence of Darwin, but as the Japanese were pushed back it was more often used in the ground attack role, keeping the isolated Japanese garrisons pinned down.
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