Columbia subject headings:
Harvard subject headings:
Great Britain. Naval Intelligence Division. Room 40.
World War, 1914-1918--Naval operations, British
World War, 1914-1918--Secret service--Great Britain
Princeton subject headings:
Great Britain. Naval Intelligence Division. Room 40
World War, 1914-1918--Naval operations, British.
World War, 1914-1918--Secret service--Great Britain.