Columbia subject headings:
Merchant marine--Germany--History--20th century.
World War, 1939-1945--Naval operations, German.
Harvard subject headings:
Merchant marine--Germany--History--20th century.
Merchant ships--Germany--History--20th century.
World War, 1939-1945--Germany.
World War, 1939-1945--Naval operations, German.
Princeton subject headings:
Merchant marine--Germany--History--20th century.
World War, 1939-1945--Naval operations, German.