In my opinion it is an original L/56 (Funcke & Bruninghaus, Ludenscheid) Kriegsabzeichen fur die Marine-Artillerie badge. Most probably a late war badge.
I agree it's a good badge. Again, a zinc example which has unfortunately lost it's finish over time.
It also might have the start of zinc pest on the wreath just under the gun barrel. I would advise you to coat the badge with vaseline, leave for 24 hours and then wipe off.
Looking for LDO marked EK2s and items relating to U-406.....
Good looking out, didn't even notice or know that vaseline would help. Thank you and history thanks you as well fo keeping it maintained correctly