When it comes to nuclear-armed submarines, the global status quo is transforming rapidly. During the Cold War and its immediate aftermath, there was more or less a dynamic equilibrium, in which sea-based nuclear forces were limited to the navies of the United States, Russia, France, the United Kingdom, and to some degree, China. But over the past several years, new players have entered the scene – including India, Pakistan, North Korea, and Israel – which means that stability is becoming challenged while the number of weapons in the arsenals of newer nuclear powers increases. This is ironic because the principal purpose of sea-based nuclear forces, in theory, is to bolster deterrence stability by increasing the survivability of one’s arsenal. Yet these weapons, when brandished by countries locked in enduring rivalries and frozen conflicts, could just as easily provoke miscalculation and accidental war due to chance encounters between nuclear-capable submarines and opposing naval forces, lapses in human judgment, and imperfect command and control.