He was first generation? Germans make up the largest cohort of all ethnic groups in the United States. Look at the names of our WWII leaders: Eisenhower, Nimitz, Spruance, King, Marshall, Halsey, Spaatz, etc...
I think that he was first generation. We never knew much about him. My grandmother was Irish, but from what I recall, was not first generation. My father had an Irish given name and a German surname.