Not doubting what you say but given these subs are virtually if not completely impossible to track while on patrol, my guess is the number of subs out there is both unknown and more then the treaty may call for.
"About reducing any nation to slag, well of course. But we need to remember that it cuts both ways particularly with regard to nations such as China and Russia. If it werent so, North Korea and Iran wouldnt be so cocky today"
Sure it cuts both ways but I am here assuming we will not be the first to use the nukes and that countries such as China, N Korea, Iran etc, knowing they face certain and total annihilation should they use them on us, will not do so. Of course a deterrent is useless without the will to use it and my guess is most of the bad guys believe we haven't the guts to pull the trigger on them. It may take the destruction of an enemy Nation State to convince the bad guys that this is the wrong country to F around with in this way.
I think we are on the same page here but the point is that deterrence is just not about numbers but rather about fulfiling your policy objectives. China has done that against the US ruthlessly by building up North Korea and against India by using Pakistan. Iran can weaken the US by subverting regimes in Lebanon and possibly Bahrain and other oil sheikdoms in the Arabian Gulf using the deterrence equation you mentioned. There’s no point in sending the whole of the Middle East to the bottom of sea if one US city is lost. Ultimately, it becomes a game of attrition.