If any of the major nuclear powers were to ever launch and all out exchange, read the 1950's novel "On the Beach" by Nevil shute

It is highly likely that the only humans (With exceptions of small pockets who would quickly pass on) left would be the crews of the boomers, the nuclear missile subs that are virtually untouchable (Well, at least the US ones are, the Russian ones seem to sink and crash a lot on their own when they are able to put to sea)

The Trident subs at sea during any particular time are much more than capable of destroying just about every living thing on earth with over 1 million times the destructive force of the bombs dropped on Japan circa 1945. This doesn't even take into consideration the four Ohio class that have been retrofitted as "Cruise missile" subs, each one carrying more nuclear tipped cruise missiles than an entire Carrier battle group

Some land based ICBMs "might' get through before the subs got them, highly doubt and bombers would,and your argument about who has the best special forces, well I hope they can dig holes real deep and kiss their as* good bye

As it was once said: I don't know what weapons WW III will be fought with, but WW IV will be with sticks and stones

These subs would launch, their missiles would get through and .........