Why is the US still using a Nazi tall ship?

Driving home along the coast of Connecticut one winter's evening, Tido Holtkamp saw a ghost. 

There she was - moored in the harbour, her three towering masts, draped with those familiar sails he had rigged back in the German Navy in World War Two.

Her body had been repainted in the red, white and blue of the US, but her curves were unmistakable. ...