Using newly released documents, the author presents an integrated look at American nuclear policy and diplomacy in crises from the Berlin blockade to Vietnam. The book answers the question of why, when the atomic bomb had been used with such devastating effect against the Japanese Empire in 1945, American leaders put this most apocalyptic of weapons back on the shelf, never to be used again in anger. It documents the myopia of Potomac strategists in involving the US in wars of attrition in Korea and Southeast Asia, marginal areas where American vital interests were in no way endangered. Despite the presence of hundreds, then thousands of nuclear bombs and warheads in the nation's stockpile, the greatest military weapon in history became politically impossible to use. And yet overwhelming nuclear superiority did serve its ultimate purpose in the Cold War. When American vital interests were threatened - over Berlin and Cuba - the Soviets backed down from confrontation. Despite errors in strategic judgement brought on by fear of Communist expansion, and in some cases outright incompetence, the ace in the hole proved decisive.