Winterbotham, F. W. Secret and Personal (London: Kimber, 1969).
Winterbotham, F. W. The Ultra Secret (London: Weidenfeld & Nicolson, 1974).
Wise, David, and Ross, Thomas B. The Invisible Government (London: Cape, 1965).
Wise, David, and Ross, Thomas B. The Espionage Establishment (New York: Random House, 1967).
Yardley, Herbert O. The American Black Chamber (New York: Ballantine, 1981).
Yergin, Daniel. Shattered Peace (London: Deutsch, 1978).
Young, Kenneth. The Diaries of Sir Robert Bruce Lockhart: Vol. I 1915 – 1938 (London-Macmillan, 1973)