Celebrated for its role alongside the Hawker Hurricane in defending British skies in 1940, the agile Spitfire soon took on an offensive role, conducting fighter sweeps across the English Channel. But in late 1941 the new German Focke-Wulf Fw-190A threatened Allied operations over occupied Europe, as it outperformed Spitfire Mark Vs serving in frontline squadrons. British aircraft designers rushed to introduce new Spitfire variants with two-stage supercharged Merlin engines, which significantly boosted the fighter’s performance. The Mark IX began operations in June 1942, and its improved speed, climb rate, and high-altitude capabilities made it a match for the Fw 190A. Designers continued to improve the Mark IX with stronger engines, jettisonable drop tanks, and gyroscopic gunsights. Spitfires accounted for nearly half of Allied fighter strength on D-Day, and the Mark IX continued to serve until war’s end.