Very difficult to be sure. NOT a standard Kriegsmarine issue cap. Possibly original to the period private purchase. You'd need better images of the sweatband, details of the band stiffening material etc. Guess its an fixed top - issue pieces had removable tops.
Personally I'd always recommend waiting for a 100% textbook official issue piece, as they are not rare.
At best a Bundesmarine re-work, at worst a ground up repro.
NEC SOLI CEDIT