From the first large-scale Viet Minh offensive against the French in 1950, to the fall of Saigon in 1975, the United States tried desperately to understand the nature of the fierce Communist-led struggle to create a unified, independent Vietnam. American intelligence played a key role in gathering information on the political and military situation in Vietnam and on the strengths and weaknesses of both sides. But as George Allen shows in this eye-popping memoir, intelligence appraisals were consistently ignored or rejected by policymakers in every administration from Eisenhower through Nixon...