Columbia subject headings:
Harvard subject headings:
Cryptography--Great Britain.
Cryptography--Japan.
Cryptography--United States.
Great Britain. Government Communications Headquarters--History.
Machine ciphers.
ULTRA (Intelligence system)
World War, 1939-1945--Cryptography.
World War, 1939-1945--Electronic intelligence.
Princeton subject headings:
Bletchley Park (Buckinghamshire, England)--History.
World War, 1939-1945--Cryptography.
World War, 1939-1945--Electronic intelligence--Great Britain.
World War, 1939-1945--Personal narratives, British.
World War, 1939-1945--Secret service--Great Britain.