In late 1941 some RAF pilots had reported seeing a new type of German fighter that could fly faster, turn tighter and climb steeper than the then standard Messerschmitt Bf109. At first British intelligence officers could make little of the reports, based as they were on fleeting glimpses in combat situations. By the end of the year, however, it was clear that the Germans now possessed a fighter that was superior in every way to the Spitfires and Hurricanes of the RAF – and that it was entering service in increasing numbers. The RAF had a tiger by the tail.
The answer, or at least a partial answer, came in the form of the Spitfire MkIX. This had an uprated Merlin engine developing 1565hp, as opposed to the 1030hp of the engine in the Spitfire MkI. It was faster than the existing Spitfires, with an edge in terms of speed and height over the FW190. However, the Spitfire MkIX was less nimble than its opposition and could not climb as quickly. Each fighter had its advantages, but overall were evenly matched.
A second new fighter joining the RAF in 1942 was the Hawker Typhoon. This was a larger, heavier aircraft but mounted a massively powerful engine. The RAF had high hopes for this machine, but it soon proved to be less effective at high altitude than had been hoped. Its performance at low altitude was, however, superlative.
from Heroes of RAF Fighter Command in Kent by Rupert Matthews