This popped up in my Twitter feed via Driftglass:
There were some US citizens who were members of the Waffen-SS, but no unit made up of American volunteers was ever raised (despite some claims about an “American Free Corps” or “George Washington Brigade”). According to figures from the SS five US citizens served in the Waffen-SS in May 1940, but after that date no numbers are available. [...]
At least eight American volunteers are known to have been killed during their service.
Numerous ethnic Germans who were born in the USA served in the Wehrmacht, for example Boy Rickmers who was born in New York and won the Knight’s Cross as part of 320. Infanterie-Division on 26 March 1943.
The big difference between World War II and the war on terror is the open-endedness of the current war, making these war powers especially dangerous.