Columbia subject headings:
Harvard subject headings:
Germany. Kriegsmarine--Submarine forces.
Submarines (Ships)--Germany--History.
World War, 1939-1945--Naval operations, German--Submarine.
Princeton subject headings:
Submarines (Ships)--Germany.
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Naval operations--Submarine.