Britain’s answer to the Focke-Wulf 190 the IX was a stop-gap project to put the new Merlin two-stage supercharged engine into a Mk V airframe. The IX was kept in production far longer than anyone imagined and formed the bulk of Fighter Command’s equipment during the middle war years. The IX came in versions for low altitude combat with clipped wings and for high altitude with extended wing-tips as well as the mass-produced normal fighter version. Normal armament was two cannons and four .303 calibre machine-guns, although the “E” wing was introduced on the MK IX giving an armament of two cannons and two heavy calibre .50 machine-guns that gave much better range and penetrating power than the earlier rifle calibre machine-guns. At medium and high altitude the IX was superior to the FW190 although the Focke-Wulf excelled at low altitude. Later “long-nosed” versions of the FW190 regained the edge over the Mark IX but by then still improved Spitfires were waiting in the wings to regain mastery of the air. It was the Mark IX that began the process of establishing air superiority for the Allies over Europe, an air superiority extended and maintained by the long range American Thunderbolt, Mustang and Lightning fighters. One Mk IX was fitted with floats as used on the Mk V floatplanes and had the same modifications to the tail. It was reconverted to a landplane after trials during 1944. In all 5,665 Mark IX Spitfires were produced.