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I A n alert of nuclear forces during a superpower crisis serves two related purposes. The military purpose is to enhance one’s readiness for war: alerting nuclear forcesreduces their overall vulnerability to attack and prepares them for potential use. The political purpose is to enhance deterrence: nuclear alerts have been used to signal resolve in a crisis and to demonstrate how seriously a government regards the stakes involved in a potential conflict. In theory, these two objectives are complementary. In practice, however, a number of strategic tensions may exist. Actions taken for purely military considerations may, under some circumstances, contradict or exceed the political signal that is desired. Conversely, the political restraints placed upon operational preparations in a crisis may, under other circumstances, unintentionally reduce force readiness. In any future military crisis with the Soviet Union, American decisionmakers are likely to perceive a severe tension between the need to alert nuclear forces in order to reduce vulnerabilityand signal resolve and the fear that such actions could move out of control, increasing the likelihood of tragic accidents, inadvertent escalation, or nuclear preemption. A good deal of attention has been given, in both the academic and the policymaking communities, to the complex set of strategic issues surrounding a decision to use nuclear weapons if deterrence fails. Far less thought has focused on the issues surrounding a decision to alert nuclear forces if a failure of deterrence appears likely. This article seeks to examine some of these issues by looking at three cases-in May 1960, October 1962, and October 1973-in which the United States government placed its global strategicnuclear forces Scott D. Sagan is a Council on Foreign Relations International Affairs Fellow serving in the Nuclear and Chemical Division, Plans and Policy Directorate (J-5),of the Organization of the Joint Chiefs of Staff. This article was written when he was a postdoctoral fellow on Harvard University’s Avoiding Nuclear War Project. The author would like to thank the working group of the Avoiding Nuclear War Project at Harvard University, as well as Richard K. Betts, McGeorge Bundy, Raymond L. Garthoff, Alexander L. George, Vice Admiral Jerome H. King, Jr., USN (ref.),and Major Steven R. Sturm, USAF, for their helpful comments on an earlier draft. International Security, Spring 1985 (Vol.9, No. 4) 0162-28891851040099-41$02.50/0 01985 by the President and Fellows of Harvard College and of the Massachusetts Institute of Technology. 99 International Security I 100 on a higher state of command readiness during an international crisis.' An examination of what went right, and of what went wrong, when nuclear forceswere alerted in the past can neither provide policymakers with effective rules of crisis management nor eliminate the inherent risks and uncertainties involved in nuclear alerts. Indeed, if nuclear alerts entailed no risks at all, they would be unlikely to contribute to deterrence at all. At the same time, an improved understanding of the problem and enhanced control over the alerting process can reduce unnecessary dangers and promote better management of superpower crises if they occur despite all efforts to prevent them. The DEFCON System The process by which American military forces are placed on alert is called the Defense Condition (DEFCON) system. There are five DEFCONS, or gradations of alert. It is difficult to outline with any degree of precision the preparations that take place under the five DEFCONs for three reasons. First, the complex set of military preparations that make up each of the DEFCONs varies between different unified and specified commands in the American military command system because the commanders often face different threats, plan different missions, and maintain different weapons systems. Secondly, the gradations of the system have been greatly altered over time as new weapons systems have been deployed, new communications capabilities have been created, and new strategic threats have emerged. Thirdly, and most importantly, the precise details of the DEFCON system are, with good reason, kept highly classified. At the general level, however, it is known that most American forces are kept at the lowest alert status, DEFCON5, in normal peacetime. The Strategic Air Command (SAC),an exception, is routinely kept at DEFCON 4.Military forces located close to...