Columbia subject headings:
Harvard subject headings:
Bletchley (Buckinghamshire, England)--History.
Great Britain. Government Communications Headquarters--History.
Lorenz cipher system
World War, 1939-1945--Cryptography.
Princeton subject headings:
Bletchley (Buckinghamshire, England)--History.
Great Britain. Government Communications Headquarters--History.
Lorenz cipher system.
Military intelligence--Great Britain--History--20th century.
World War, 1939-1945--Cryptography.