"Atomic explosions in the atmosphere can disrupt radio communications. Missiles at the time were controlled by ground-based computers, so huge amounts of radio interference made America's ability to direct a second volley of fission sandwiches unreasonably hard. And on the other side of such an exchange, not being able to control your rockets can make mutual assured destruction up to 50 per cent less mutual. What's the fun in that?"
An awesomely funny article from the talented folks at the Reg, go read it in full.