An anonymous reader points out a story in Wired introducing us to the Doomsday Machine built by the Soviet Union
in the 1980s — and that remains active to this day. It was called "Perimeter." The article explains why the device was built, and why the Soviets considered it to be something that kept the peace, even though they never told the US about it. "[Reagan's] strategy worked. Moscow soon believed the new US leadership really was ready to fight a nuclear war. But the Soviets also became convinced that the US was now willing to start a nuclear war. ... A few months later, Reagan... announced that the US was going to develop a shield of lasers and nuclear weapons in space to defend against Soviet warheads. ... To Moscow it was the Death Star — and it confirmed that the US was planning an attack. ... By guaranteeing that Moscow could hit back, Perimeter was actually designed to keep an overeager Soviet military or civilian leader from launching prematurely during a crisis. The point, [an informant] says, was 'to cool down all these hotheads and extremists. No matter what was going to happen, there still would be revenge. Those who attack us will be punished.'"