Real differences were found in national extraction and possibly in education. The principal extraction in all flyers was Old American, with the rest overwhelmingly Northwest European - British, Irish, Germanic, and Scandinavian, in that order. Four per cent were of Slavic and 1% of Mediterranean descent. Successful combat pilots were significantly more Old American in ancestry than cadets, an Old American being a person whose 4 grandparents were born in the United States. Twenty-two per cent of cadets and 60% of the successful combat pilots were Old American on both sides; on one parental side only, an additional 24% and 15%, respectively. This highly significant difference (p < .01) is hardly attributable to geographic provenience, since 10% more of the combat pilots than of the cadets were from the East coast, where recent immigrants are most numerous. Old Americans may have tended to become pilots rather than bombardiers or navigators. The greater metrical homogeneity of pilots as compared to the latter groups (tables 1 and 4) lends some support to this hypothesis; but even so, with twice as many pilots in the AAF as bombardiers and navigators combined, pilots should resemble cadets in national extraction more closely than they did. If Old Americans actually were more successful in military flying - still an assumption awaiting confirmation in larger samples - were they eliminated less often from training? Had they “sounder” personalities; or do the physical traits associated with flying success occur more often or more strongly among Old Americans? Any one of these possibilities might repay further study.
[Damon. Physique and success in military flying. Am J Phys Anthropol. 1955 Jun;13(2):217-52.]
A truly odd bit of data emanating from the war was the fact that aces (those with five or more air-to-air kills) tended to have blue or light-colored eyes (over tow thirds) [. . .]
[James F. Dunnigan and Albert A. Nofi. Dirty Little Secrets of World War II]