One of the serious risks associated with the strategic nuclear arsenals of Russia and the United States is that an accidental launch might result from a false alarm or from misinterpreting information provided by an early-warning system. This risk will not be reduced by bringing down the number of strategic missiles on high alert to the level of about 500 warheads on each side because this measure will not significantly affect first-strike vulnerability of the Russian strategic forces. Other measures that have been suggested so far, namely an upgrade of the Russian early-warning system, establishing additional channels of real-time exchange of early-warning data, or transparent and verifiable de-alerting of strategic forces, are more likely to increase the probability of an accident than to reduce it. To address the problem of an accidental launch in the short term, the United States and Russia, while continuing to work toward deep reductions of their strategic nuclear forces, should develop and implement...