Columbia subject headings:
Harvard subject headings:
Cryptography--History--20th century.
Enigma cipher system--History.
ULTRA (Intelligence system)
World War, 1939-1945--Cryptography.
World War, 1939-1945--Electronic intelligence.
Princeton subject headings:
Cryptography--History--20th century.
Enigma cipher system--History.
ULTRA (Intelligence system)
World War, 1939-1945--Cryptography.
World War, 1939-1945--Electronic intelligence.