I have seen this picture and would like a more detailed answere myself,but in all my U-boat books this is all that I could find \"The casing has been recessed forward to reduce the deck area of the U-883 ( type IXD2 ) to aid more rapid diving. In the recess is fitted the acustic hammer which was operated ,while submerged, by a water-activated propeller\". The following was found in the book NAVIES OF THE SECOND WORLD WAR GERMAN SUBMARINES VOL. 1 by H.T. LENTON , MACDONALD&CO. LTD. 1965, page111. It is too small to be a storeage container and does not have all the features to be a mine paravane., could this \"acustic hammer \"have been used to detonate acustic mines or torpedoes ?