Columbia subject headings:
Harvard subject headings:
Germany. Kriegsmarine--History--World War, 1939-1945.
Submarine warfare--Germany--History--World War, 1939-1945.
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Naval operations--Submarine.
Princeton subject headings:
World War, 1939-1945--Naval operations--Submarine.