Just ran across an interesting table in Dean's "America's Hundred Thousand" that I had not digested before since I have only owned the book about ten years. LOL For those not familiar, the book is about the approx. 100000 fighters the US built during WW2 and is voluminous. The part of the table I will tack on here rather than start a new thread shows the date a contract was awarded for that particular fighter and the date of first combat. Here it is:
F4F/FM, July 28, 1936, December, 1940.
F2A, June 22, 1936, April, 1940
P40, July 30, 1937, May, 1941.
P38, June 23, 1937, August, 1942
P39, October 7, 1937, April, 1942
F4U/FG, June 11, 1938, February, 1943
P51, May, 1940, July, 1942
P47, September 6, 1940, , April, 1943
P61, January 30, 1941, June 1944
F6F, June 30, 1941, August, 1943
P63, June 27, 1941,
The interesting point to me is that every fighter was in development before the war began for the US. Apparently the P63 never saw combat.