During World War II the United States and Great Britain signed secret pacts agreeing to merge the code- and cipher-breaking (cryptanalytic) operations they were directing against Nazi Germany, Italy, and Japan. This partnership was unique: never before had countries revealed their intelligence methods and results even to their closest allies. Cooperation between countries on something this sensitive is approached with extreme caution. The budding relationship was hampered by rivalries, doubts, and suspicions; there was much strain between London and Washington, and bitter rivalries between the U.S. Army and Navy. But the vital enterprise went forward, making highly important contributions to Allied victory.\nThe benefits of the Anglo-American partnership extended far beyond wartime: the Ultra-Magic deals were the beginning of a long-term special relationship. Faced with severe budgetary considerations, tensions with the USSR, and fears of a nuclear Armageddon, the British and Americans hammered out a secret charter for a permanent intelligence agreement that helped shape the world during the long Cold War.\nInformation on secret intelligence in both the wartime and postwar periods has been tightly controlled by both governments until recently, and has rarely been studied by scholars. Bradley Smith has searched both British and American archives and examined in detail this most secret intelligence cooperation: the state of Anglo-American relations at the start of World War II, how the delicate bond was formed, how the Ultra-Magic deals operated, and why the secret relationship survived and thrived for half a century. Extremely well researched and clearly presented, this study fills an important gap in the literature on Ultra and Magic. It is a fascinating study of the politics, personalities and technologies of secret intelligence.