Columbia subject headings:
Harvard subject headings:
Submarines (Ships)--Germany--History--20th century
World War, 1939-1945--Campaigns--Atlantic Ocean.
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Naval operations--Submarine.
Princeton subject headings:
Germany. Kriegsmarine
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Naval operations--Submarine.