from back cover:
Told from confidential documents--some of which remain closed for the foreseeable future--here is the precisely detailed story of the British government's campaign of strategic deception of the German High Command.
By 1943 the Germans were almost wholly dependent on double agents for news of what was happening in the United Kingdom: intercepted and decrypted radio traffic showed the Allies how extensively the enemy was accepting disinformation and acting on it. In Britain, extremely tight communications security made possible the apprehension and control of virtually all active enemy agents.
Sir Michael Howard explains how the British were able to deceive the Germans about the strategic intentions of the Allies and make them greatly overestimate Allied resources.