Columbia subject headings:
World War, 1914-1918--Naval operations, German.
World War, 1914-1918--Naval operations--Submarine.
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Naval operations--Submarine.
Harvard subject headings:
Germany. Kriegsmarine.
World War, 1914-1918--Naval operations, German
World War, 1914-1918--Naval operations--Submarine
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Naval operations--Submarine.
Princeton subject headings:
Germany. Kriegsmarine
Submarine warfare.
World War, 1914-1918--Naval operations, German.
World War, 1914-1918--Naval operations--Submarine.
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Naval operations--Submarine.