I found the information below on a very interesting site, if it's true we should really all be crapping ourselves.
According to Jane’s Intelligence Review, if Moscow looked like it was under attack or even of command links to key Russian leaders were interrupted , Perimeter would automatically launch a communications missile that would in turn transmit the codes to launch thousands of nuclear weapons.
McSpotlight: However, the governments of Russia and the USA have signed an accord saying that any holocaust resulting from this will be entirely accidental and unintended and that no grudges will be maintained by the surviving members of those two nation states.
So, you may get annihilated, but it's won't be on purpose. So that's all right, then...