In October 1973, an unreliable radiation detector could have caused the end of the world. The setting was the Yom Kippur War between Israel and a coalition of Arab states, and the superpowers found themselves being sucked into the conflict. In the war’s febrile final days, the United States detected what appeared to be radiation from a Soviet freighter headed for Egypt and concluded—almost certainly incorrectly—that Moscow was transferring nuclear warheads to Cairo. Partly in response, on Oct. 24, Washington placed its nuclear forces on a global alert for only the fourth time in history—a step it has taken only twice since. The U.S. alert prompted the Soviet Union to reportedly issue a preliminary order to begin the alerting of its own nuclear forces.
This chain of events, which could have culminated in a nuclear war, provides a timely warning. The United States’ ability to detect and track nuclear warheads has improved immeasurably over the last 46 years, making an exact replay of 1973 unlikely. However, growing entanglement between nuclear and nonnuclear weapons is exacerbating closely related dangers. In particular, nuclear-armed states are relying ever more heavily on dual-use weapons, which can accommodate nuclear or nonnuclear warheads, thus exacerbating the risk that one side might wrongly conclude that another had deployed nuclear weapons. In a crisis or conflict, the result could be an escalation spiral that, unlike in 1973, spins all the way to nuclear devastation...