I am a bit skeptical. Here's my reasons. the stamp on the inside is very fresh; leading me to possibly believe that this might be an original but unworn example. Now, I see a tradition badge, possibly from a U-boat or other ship. This is affixed to a minty hat.
I am not experienced enough to comment on the originality of the hat. However, I am just sharing my suspicion that this might be a post put together hat. Most likely, with a post war fabrication of a U-boat insignia attached.