I have always found this sort of a discussion very hard to deal with. What is the response strategy? The thought of someone launching a comprehensive first strike in the first place seems so far fetched that I can't imagine it ever happening. Then retaliation. Then a second strike? Adding further to the destruction - would any sane leader do so? Is sanity the question?

I think that Pakistani wants to know if having some sub launched nukes would be enough incentive for India not to launch a first strike. Given that India is a democracy, I would say yes. The destruction or ruination of even a single large city would have a strong political impact, almost certainly enough to get the ruling party(ies) outed. If multiple cities were hit, then even more so. Even the claim of a pre-emptive strike would probably not be enough for the millions of people who have lost family and friends to nuclear hellfire. In this case, even if the first strike was "reasonable", don't count on people thinking that way. Emotion would take over. This should be factored in.

Let's backtrack a bit and review terms. First strike and second strike are reasonably self explanatory. A first strike means using nuclear weapons first. When used against an enemy with it's own nuclear capability, the logical expectation is that a first strike will have as part of it's target list, destroying the ability of the enemy to respond with a nuclear strike of it's own. So, first strike came to mean the (presumed) ability to use nuclear weapons not just to devastate an enemy, but, specifically, to destroy his own ability to use nuclear weapons. Any retaliatory strike, a nuclear attack in response to a previous nuclear attack, is a second strike. Second strikes happen because the first strike did not find all the weapons, or didn't destroy them, or didn't know they were there in the first place. Or, for some reason, chose not to try to destroy them. What some may be confusing is a second strike from a secure second strike capability. The latter term is used to denote a nuclear capability which it is believed can not be destroyed by a first strike. The search for a secure second strike capability is what led, first, to hardening land based missile silos, to the placing of nuclear missiles on submarines, and to the creation of mobile land based systems. Insofar as deterrence theory is concerned, the logic is that if a country has a secure second strike capability, it has a strong deterrent against being attacked in a first strike. That's because the nature of a secure second strike capability guarantees the ability to answer a first strike with a nuclear response. Now, it's important not to be confused by these terms and their use. A claim that a second strike capability exists is not the same thing as the actual existence of such a capability. Technology evolves, and what may have been such a capability at one time may not be so, later. Or, it may never have existed save in the minds of some publicity people and politicians. The difficulty in achieving certainty of whether any such capabilities exist is part and parcel of deterrence theory. Orthodox theory maintains that a bit of uncertainty doesn't obviate deterrence. In conventional settings, doubt of the strength of one side or other may not stop anything from happening. Leaders may be willing to take chances. (Historically speaking, of course, they have and continue to do so.) But, the argument ran, in context of robust nuclear forces, the risks of use are so great that no sane leader would risk the complete destruction of his country (or, of the world) if there weren't complete certainty of the outcome of use. This led to an expression to the effect that a little uncertainty could be a good thing. Western theoreticians said that a good leader in the nuclear age had about him enough of an air of craziness that a potential enemy had to worry about what he might do. But, no so much that it looked as if there was no way to deal with him, or satisfy him, or that he appeared unstable. What they didn't want was some greatsoul who cared so much that everyone would conclude that he just didn't have the stones to give orders if the time came. Such a leader would surrender, preemptively. However, the entire edifice of deterrence theory, as applied during the Cold War rested on some assumptions as to how leaders acted. These assumptions, sometimes called the Rational Actor Model, are not always valid. Considerations which usually obtain in the West, and even had some validity over the Soviet Union don't necessarily to all leaders in all places under all circumstances. For instance, mindsets tend to change, in war, and risks which seem irrational in peacetime may come to be seen as acceptable after the fighting starts. This is a very common experience in history. Then, after wars start and losses pile up, some leaders can get a little crazy. Some get a lot crazy. Neither Germany nor Japan entered WW2 expecting or intending to lose. Nevertheless, by the late days, Hitler was muttering "Let it burn. The Germans don't deserve me. Let them all burn." And, the Japanese militarist clique was preparing for the utter destruction of the whole country in a giant act of seppuku. Not just the conquest of Japan, but virtual annihilation of the entire people, rather than accept the dishonor of surrender. And, then there are those nice folks who sit around contemplating how to bring about the end of the world, or, just the end of civilization as we know it. Let's fight, and if the world ends, then it's what Allah really wants, anyway. The traditional logic of deterrence theory as formulated during the Cold War does not necessarily work when the other side is a Khomeini or a Bin Laden.

Massive's note goes some way to explaining why Herman Kahn's seminal book was titled, THINKING ABOUT THE UNTHINKABLE. Simply refusing to consider the real possibilities is a poor way to run a country. Bad things can happen even if you don't want them to and refusing to believe that something is possible does not, thereby, render it impossible.

Good point on the necessity of a leader being perceived to be willing to counter-launch. And thanks for helping to explain the terms.