WWII German U Boat Badge 

The WWII German U-Boat Badge (U-Boot-Kriegsabzeichen) was a military decoration awarded to members of the Kriegsmarine (German Navy) who had served on U-boats during World War II. It was instituted on October 13, 1939, by Grand Admiral Erich Raeder.

This was awarded to U-boat crew members who had completed three operational patrols.

Maker marked - Frank & Reif, Stuttgart