Germany didn't send out its navy ships, but it did send out raiders around this time: there was a freighter from South America I think that was seized by the Navy (I think it was Brazilian or something - hauling bananas

) and converted to a raider. Lasted 'til 1918 and successfully made it back to port. I can't remember but I think she was called the Sea Wolf or something like that. Yeah, I know, there's computer games with that name, but this was for REAL. Can't remember the name of the book about her.