KM kriegsmarine sailor cap Tellermütze real of Bundes/Volksmarine?

[glaser]

This removable blue cap of a sailors cap has a white stamp: K 55

Can somebody confirm this as Kriegsmarine, Bundesmarine (postwar West-Germany) or Volksmarine (postwar East-Germany) please?

Opinions are nice, but I prefer anwers based on evidence or documents!

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