Well, from the Wiki article:boredatwork wrote: Was Prinz Eugen ever officially "USS"? I don't think she was ever comissioned as an active ship in the US Navy - Likewise I've never heard of Nagato being "USS Nagato."
"She was awarded to the United States and commissioned into the US Navy as the unclassified miscellaneous vessel USS Prinz Eugen (IX-300)."