Columbia subject headings:
Harvard subject headings:
Great Britain--History, Military--Sources--Bibliography--Catalogs.
Great Britain. Directorate of Intelligence--Archives--Catalogs.
Great Britain. Public Record Office--Catalogs.
World War, 1939-1945--Secret service--Great Britain--History--Sources--Bibliography--Catalogs.
Princeton subject headings:
Great Britain. Directorate of Intelligence--Archives--Catalogs.
Great Britain. Public Record Office--Catalogs.
World War, 1939-1945--Secret service--Great Britain--History--Sources--Bibliography--Catalogs.