A thoughtful post from the OP. Minor critique is that it's a bit of a chunk to get through but worth the read. In response, amazingly, I've actually bothered composing a proper reply.
I, for one, am grateful for the Vanguard class submarines patrolling the waters silently protecting our land.
I believe they would be used in response to an all-out nuclear attack on the UK, simply because it would be an almost-automatic response from our subs if we knew where the missiles came from. That said, I'm not actually sure how much autonomy the Captain of nuke sub gets in terms of whether to fire the missiles if the UK is nuked and there's no other chain of command. Let us hope and pray, we never have to find out. I would assume his authority is absolute depending on the content of the "Letter of last resort."
In terms of nuclear warheads being fired for the completion of non-nuclear strategic aims it's very very doubtful. A nuclear first-strike is almost impossible to justify on so many levels:
- Firstly, it's a massive escalation of the situation even with a low yield weapon.
- Secondly, to get the certainty of intelligence necessary to launch a strike of that magnitude is almost impossible. Remember Iraq? Intelligence can be flawed, manipulated or flat-out wrong.
- Thirdly, even ISIS having a nuclear weapon is a very different scenario from it being enough of an immediate threat to the UK to justify a nuclear pre-emptive strike they have no means of delivery that would make the threat imminent.
SS