Columbia subject headings:
Germany. Kriegsmarine--Submarine forces--History--20th century.
Submarines (Ships)--Germany--History--20th century.
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:
Submarines (Ships)--Germany--History--20th century
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 forces--History--20th century.
Submarines (Ships)--Germany--History--20th century.
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.