Columbia subject headings:
Harvard subject headings:
Armed merchant ships--England--History--20th century.
Armed merchant ships--Germany--History--20th century.
World War, 1939-1945--Naval operations, British.
World War, 1939-1945--Naval operations, German.
Princeton subject headings:
Academic theses.
Armed merchant ships--England--History--20th century.
Armed merchant ships--Germany--History--20th century.
World War, 1939-1945--Naval operations, British.
World War, 1939-1945--Naval operations, German.