"Alberich" consisted of black rubber tiles with holes of various diameters which acted as sound absorbing coating over the entire hull. This coating reduced reflections from British ASDIC and made submarines harder to detect. It was still in the experimental stage when the war ended but a total of 14 submarines were fitted with the coating from 1941 onwards. This included a couple of Dutch submarines, U11, a Type II submarine, several Type VIIc boats, U480 to U485 built in Kiel and a batch built by B & V in Hamburg plus several Type XXIII, one of which was sunk in a Tallboy attack on the Fink II U-boat bunker at Kiel in 1945.