Everybody sees armageddon as a general thermonuclear exchange between the superpowers. I don't see it that way. Once the command is convinced a full first strike is on the way, I believe either side will do nothing until they have reports of a confirmed hit on an actual target. If there's going to be a nuclear war, it won't hurt to lose a few silos to make sure its for real. In fact, I think enormous casualties will be absorbed before the commanders launch the submarine missiles (the ones most likely to survive a first strike) in retaliation.

What is more likely to happen IMO is an accidental launch of a tactical nuke on some battlefield or out at sea that suddenly escalates as mid-level commanders start seeing their front-line units winking off the boards. Once nuclear weapons are deployed on the tactical battlefield, it will only be a matter of hours before it escalates to strategic missiles. Remember, it won't be just two opponents involved, there will be several other countries already at full alert when the first balloon goes up. A lot of fingers will be on the trigger.