WW2 German Kriegsmarine Coastal Artillery badge by the much appreciated, amongst collectors, manufacturer Schwerin Berlin. Nava badges from Schwerin are reknowned for their high level of detailing, the way that they maintain their gilding / wash after many years and their robust hinge and pin set up (you dont find many with a broken / repaired reverse).
Note -> As always the problem with being a much appreciated antique badge is that they are also the first to be copied and reproduced. From the images shown below there is more than enough detail to make a comparison for authentication purposes.