Columbia subject headings:
World War, 1914-1918--Germany.
World War, 1914-1918--Naval operations--Submarine.
Harvard subject headings:
World War, 1914-1918--Germany.
World War, 1914-1918--Naval operations--Submarine
Princeton subject headings:
World War, 1914-1918--Germany.
World War, 1914-1918--Naval operations--Submarine.