Martin Hellman Stanford University Inventor, Diffie–Hellman key exchange There has not been a world war since 1945, the year in which nuclear weapons came into existence. Those two facts, conflated into one, have led top American officials to repeatedly call nuclear deterrence “the cornerstone of U.S. national security.” But, given that a failure of this strategy would threaten the very existence of our homeland, it is surprising that no one knows how much risk it entails. An engineering discipline known as quantitative risk analysis (QRA) teases much more information from the available data than might first appear possible, and indicates that the risk may be highly unacceptable. QRA is also useful for highlighting innovative ways to reduce the level of nuclear risk.