Frank Luke's Civil War Grandfather?

[Ritterton]

Almost hate to start this thread, as I fear maybe this is answered elsewhere but my searching efforts have not found the answer, but here it goes.

Norman Franks' American Aces notes that Frank Luke's grandfather had served in the Union Army during the Civil War. Pg 73.

Here is my question, what was his name and his regiment? The implication is that he was German, and there were very specific German regiments organized for the Union. I manage a website about one of those (74th PA Volunteers - First German). Thus the curiousity and question.

Thanks in advance.

R