Columbia subject headings:
Harvard subject headings:
Deutschland (Submarine)
Merchant marine--Germany--History--20th century.
World War, 1914-1918--Naval operations, German
World War, 1914-1918--Naval operations--Submarine
Princeton subject headings:
Deutschland (Submarine)
Merchant marine--Germany--History--20th century.
World War, 1914-1918--Naval operations, German.
World War, 1914-1918--Naval operations--Submarine.