Columbia subject headings:
World War, 1939-1945--Cryptography--Congresses.
World War, 1939-1945--Secret service--Germany--Congresses.
World War, 1939-1945--Secret service--Great Britain--Congresses.
Harvard subject headings:
World War, 1939-1945--Cryptography--Congresses.
World War, 1939-1945--Secret service--Germany--Congresses.
World War, 1939-1945--Secret service--Great Britain--Congresses.
Princeton subject headings: