what other aircraft were essential?
How about that other British inspired aircraft, the P-51. Albeit, built in the US, it was designed at the behest of the British, and they paid with hard coin for its development and production, until lend lease cut in. It was because of Rolls Royce test pilot, Ronnie Harker, that the Merlin was introduced, and the Merlin version was seen as a counter to the FW 190. Consideration was even given to setting up a production line in Britain. And it was the sole aircraft to perform the long range escort, both in Europe and the B-29 raids on Japan. An essential aircraft? In my books, the best, and all thanks to the British. Without them the aircraft would not have existed, and I wonder what course the war may have taken without it.