"Rawl was the Irish American son of a New Jersey truck driver who had enlisted in the United States Marines, made sergeant, and then...".
I first assumed it was Rawl's father, the truck driver, who had enlisted in the United States and all, but then it became clear later in the book that it was Rawl who was the US Marine.
Your initial assumption was natural. You assumed that the antecedent of "who" (i.e., what "who" refers to) was the noun phrase "truck driver" rather than "Irish American son." Grammatically, either one can function as the antecedent.
The easiest way to parse it is to see the relative clause ("who had enlisted . . .") as modifying the entire noun phrase "the son of a New Jersey truck driver," the head of which is "son," not "truck driver." "Truck driver" is part of the "of"-phrase.