The german u boat fleet developed into one of the most effective weapons of the third reich in its war with the allies and for several months the u boats seemed to dominate the atlantic in october 1939 admiral karl d nitz commander in chief of the german u boat fleet ordered lieutenant gunther prien captain of the u 47 to the heavily guarded base of the british home fleet at scapa flow in the orkneys in the night of 1314 october the u 47 surfaced to travel through the barricaded kirksand