Columbia subject headings:
Documents on microfilm--Bibliography.
Submarines (Ships)--Germany--History--Bibliography.
World War, 1939-1945--Germany--Sources--Bibliography.
World War, 1939-1945--Naval operations, German--Bibliography.
World War, 1939-1945--Naval operations--Submarine--Bibliography.
Harvard subject headings:
Princeton subject headings:
Documents on microfilm--Bibliography.
Submarines (Ships)--Germany--History--Bibliography.
World War, 1939-1945--Germany--Sources--Bibliography.
World War, 1939-1945--Naval operations, German--Bibliography.
World War, 1939-1945--Naval operations--Submarine--Bibliography.