They built it in the 1980s, and it's still around. Nicholas Thompson explores the paradoxical nature of nuclear weaponry:

[O]ne 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.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.