In the 1980s, the Soviets built a Doomsday Machine – and it's still active. I learned about it while researching my new book, The Hawk and the Dove: Paul Nitze, George Kennan, and the History of the Cold War. It's also the subject of a story in the current issue of WIRED.

The system would have allowed the USSR to respond insemi-automatic fashion to an American nuclear strike – even one that had knocked out the Kremlin and the Defense Ministries. And one obvious question that people ask when they learn about this system is "Why didn't the Soviets tell us?" As we all know from Dr. Strangelove, the point of a Doomsday Machine is to convince the other side in a conflict that attack is futile.

The answer to that question is the most interesting thing I learned in my research. Yes, the Soviets were extremely secretive; and, yes, they were worried that, if they told us, we could disable it. But the more interesting reason is that they also built the system to deter themselves. Here's the relevant passage from the story: