Two Hawks From Earth (aka The Gate of Time)

In this classic of alternate history by grand master Philip Jose Farmer, Native American bomber pilot Roger Two Hawks bails out over enemy territory in WWII, only to find himself on another Earth-one in which the American continents never rose from the waters, and the ancestors of the American Indians remained in Asia and Europe-an Earth embroiled in a world war of its own, with Two Hawks caught in the middle.