The Mk IX replaced the Mk V from June 1942. It allowed the RAF to go back onto the offensive in occupied Europe, and resume the “circus”, “ramrod” and “rodeo” raids. Its first combat success came on 30 July 1942, when an Spitfire Mk IX shot down a Fw 190.
The Mk IX provided an alternative solution to the problem. It used the same Merlin 60/70 series engines at the Mk VIII, but in a slightly modified Mark Vc fuselage. This allowed for rapid development and production of the new model. Work on fitting the more power Merlin 61 with its two-stage supercharger had begun in the summer of 1941, and on 27 September Spitfire N3297 (the only Mk III Spitfire built) flew for the first time (the same month as the FW 190 became operational). Three marks of Spitfire would be developed from this experimental aircraft. The Mk VII and Mk VIII would use a redesigned fuselage, and this meant that they would take too long to produce. The crisis was so serious that the RAF was forced to stop all but the most important daytime operations over occupied Europe in November 1941. When operations were resumed again, between March and June 1942, losses were unacceptably heavy, and had to be stopped again.