Columbia subject headings:
Germany. Kriegsmarine.
Naval reconnaissance.
Radio, Military--Germany.
World War, 1939-1945--Naval operations, German.
Harvard subject headings:
World War, 1939-1945--Cryptography.
World War, 1939-1945--Electronic intelligence--Germany.
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Secret service--Germany.
Princeton subject headings:
World War, 1939-1945--Cryptography.
World War, 1939-1945--Electronic intelligence--Germany.
World War, 1939-1945--Naval operations, German.
World War, 1939-1945--Secret service--Germany.