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