I've heard that some (not sure of numbers) of German-Americans left the USA to join the German armed forces after Hitler took power (some reference to this is made when I've read about Operation Greif).

What happened after the war to these soldiers? Were any of them stripped of U.S. citizenship after the war? I'm a naturalized U.S. citizen myself, and I remember when I was studying for my citizenship test, there was a section prohibiting service in any foreign armed forces.