Perimeter ensures the ability to strike back, but it's no hair-trigger device. It was designed to lie semi-dormant until switched on by a high official in a crisis. Then it would begin monitoring a network of seismic, radiation, and air pressure sensors for signs of nuclear explosions. Before launching any retaliatory strike, the system had to check off four if/then propositions: If it was turned on, then it would try to determine that a nuclear weapon had hit Soviet soil. If it seemed that one had, the system would check to se if any communication links to the war room of the Soviet General Staff remained. If they did, and if some amount of time—likely ranging from 15 minutes to an hour—passed without further indications of attack, the machine would assume officials were still living who could order the counterattack and shut down. But if the line to the General Staff went dead, then Perimeter would infer that apocalypse had arrived. It would immediately transfer launch authority to whoever was manning the system at that moment deep inside a protected bunker—bypassing layers and layers of normal command authority.
So were the Russians so distrustful of us that they figured they needed that? If so, why not tell us? Dr. Strangelove would protest that there's no point to a doomsday machine if the enemy doesn't know about it.
Apparently, the Soviets didn't trust other Soviets:
The silence can be attributed partly to fears that the US would figure out how to disable the system. But the principal reason is more complicated and surprising. According to both Yarynich and Zheleznyakov, Perimeter was never meant as a traditional doomsday machine. The Soviets had taken game theory one step further than Kubrick, Szilard, and everyone else: They built a system to deter themselves.
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, Zheleznyakov 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."
Of course, in a bi-polar world, such a system is fine in theory. But in a world with many nuclear powers, what if China nuked Russia, decapitating their command and control and triggering an automatic launch against us?
