Factual error: The Japanese fighters that the AVG tangles with are Nakajima Ki27 "Kates" with a total of two 7.7mm guns. However, they are depicted in the film as having 4 wing-mounted guns.
Factual error: When Pappy tells Woody he is fired and to be on the plane out in two days, the camera pans to the desk calendar, showing Sunday, December 7th, 1941. Later, all of the AVG members listen to FDR's "day of infamy" speech. However, as far as China was concerned, being to the West of the International Dateline, Pearl Harbor was attacked on December 8th, and the speech occurred December 9th.