It's difficult to discuss the birth of Supermarine Spitfire IX without including her arch nemesis, the German Focke Wulf FW-190. During World War II, In early and mid 1941, the RAFs Spitfire V fighter was fairly well matched against the Luftwaffe's Me 109 F. That all started to change in the fall with the unexpected appearance of a very fast, heavily armed new radial engined German fighter, the FW-190. With it's revolutionary "tear drop" canopy, the 190 was a generation ahead of the Spit V and quickly established air superiority where ever it appeared.
The British already had an answer in the works, the new Spitfire VII/VII, with an airframe built around the fabulous new Rolls Royce Merlin 61 engine, which had a two speed supercharger that produced much more power and exceptional high altitude performance. Unfortunately the new Spit was still in development, so an "interim" solution had to be found to counter the scourge of the FW-190.
So Supermarine modified the proven Spit V airframe and mated it to the new Merlin 61 engine and a new four blade prop to handle all that power. The new aircraft surpassed all expectations and was in full production by the summer of 1942 . Now it was the Luftwaffe's turn to be surprised. Pouncing on what appeared to be Spitfire Vs, they encountered a new plane that accelerated and climbed like a cat, while still retaining the Spit's traditional agility. Although the Spit IX and the FW 190 each had certain advantages over the other, the balance in the air had been restored .
And far from being just an "interim" design, the Spit IX proved to be so capable that it continued in production with continuous improvements and a variety of high and low altitude models. Two variants based on the IX are featured in this manual: the PR XI photo recon plane, and the Mk XVI which was powered by a US built Packard version of the Merlin -- the same engine transplanted so successfully into the North American Mustang.
By the end of the war, the "interim" Mk IX was many RAF pilot's favorite Spit!-