Columbia subject headings:
Harvard subject headings:
Military intelligence--France--History--20th century.
World War, 1914-1918--France--Cryptography.
World War, 1914-1918--Secret service--France
Princeton subject headings:
Military intelligence--France--History--20th century.
World War, 1914-1918--France--Cryptography.
World War, 1914-1918--Secret service--France.