The Soviet strategic modernization program of the 1970s was one of the most consequential developments of the Cold War. Deployment of new intercontinental ballistic missiles and the dramatic increase in the number of strategic warheads in the Soviet arsenal created a sense of vulnerability in the United States that was, to a large degree, responsible for the U.S. military buildup of the late 1970s and early 1980s and the escalation of Cold War tensions during that period. U.S. assessments concluded that the Soviet Union was seeking to achieve a capability to fight and win a nuclear war. Estimates of missile accuracy and silo hardness provided by the U.S. intelligence community led many in the United States to conclude that the Soviet Union was building a strategic missile force capable of destroying most U.S. missiles in a counterforce strike and of surviving a subsequent nuclear exchange. Soviet archival documents that have recently become available demonstrate that this conclusion was wrong. The U.S. estimates substantially overestimated the accuracy of the Soviet Union's missiles and the degree of silo reinforcement. As the data demonstrate, the Soviet missile force did not have the capability to launch a successful first strike. Moreover, the data strongly suggest that the Soviet Union never attempted to acquire a first-strike capability, concentrating instead on strategies based on retaliation.