Here is the same for the U-Boat War Badge.
The difficulty here is the name of the BDU (which I mistakenly called FDU in the edited picture, which is quite wrong as that was abolished in 1939).
Important information:
- only the surname is printed on the thing (green).
The BDU:
Name: Karl Dönitz until the 30th January 1943, after that
Hans-Georg von Friedeburg
Rank: Konteradmiral (after 01 Oct 1939); Vizeadmiral (01 Sep 1940); Admiral (14 Mar 1942) for Dönitz. Friedeburg: Vizeadmiral (01 Feb 1943); Admiral (01 Apr 1943); Generaladmiral (01 May 1945)
I was unable to find a signature picture of Friedeburg, so that will be a problem.
I was unable to find a picture for the U-Boot Frontspange, but I suggest just replacing the top icon and the name of the award (replace the "das" above the part in yellow with "die" and the writing in yellow with Ubootfrontspange.
Regarding the location (highlighted in red):
there is no info on whether it was the base name, but since the commander of the U-boots signed it, I would simply write "Oberkommando der Kriegsmarine" (Navy Command).