modifications, was standardised on later Spitfires. This variant served almost exclusively overseas in the Mediterranean, with the Desert Air Force and the USAAF, in the South West Pacific Area, with the Royal Australian Air Force and RAF and in the South-East Asian theatre with the RAF. After the Mk IX and Mk V, the Mk VIII was the third most numerous operational variant with 1,658 examples built. Mk IX (type 361) In the early months of 1942, with the clear superiority of the Focke-Wulf Fw 190 over the Spitfire Mk Vb, there was much pressure to get Spitfires into production using the new two-stage supercharged Merlin 61 engine. In September 1941 the Spitfire Mk III prototype N3297 had been converted by Rolls-Royce at their Hucknall plant to take a Merlin 60, which had been specifically designed for use in the Wellington Mk VI high altitude bomber. The performance increase was described by Jeffrey Quill as a "quantum leap" over that of the Mk Vb and another Spitfire airframe, R6700 was modified to take the new engine. Although design work on the Mk VII and VIII series was under way, these would take over a year to get into production and a counter to the Fw 190 was urgently needed. The Air Ministry made the decision that Mk Vc airframes should be converted to take the more powerful engine and, as a result, many of the early Mk IXs were converted Mk Vcs which did not have any of the refinements which later appeared. These could be identified by the Type C wing with the large double blisters over the inner cannon bays and the identification light on the fuselage spine, behind the aerial mast. The elevator horns were also smaller in size than that of most Mk IXs which had larger horn balances. The first Mk IX was a modified Mk Vc AB505, which was tested by the Air Fighting Development Unit (AFDU) in April 1942. The report said;The performance of the Spitfire IX is outstandingly better than the Spitfire V especially at heights above 20,000 feet. On the level the Spitfire is considerably faster and climb is exceptionally good. It will climb easily to 38,000 feet and when levelled off there can be made to climb in stages to above 40,000 feet by building up speed on the level and a slight zoom. Its manoeuvrability is as good as