The International Maritime Museum Hamburg does not only have a good XXIII model but also an original prop of the class on display outside. As the rust indicates, a steel prop....the Nazis were running out of bronze at the end of the war (despite melting church bells) and had to use steel instead.

Also on disply a prop of a 206 class post war German submarine:
Also on disply a prop of a 206 class post war German submarine:
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