Now there is an ambiguity that whether the booster will ignite inside the water or after clearing the water. Both are possible, but I believe that it would be easier (at first) to ignite the booster inside water.
@The Deterrent
Usually there is a separate motor that ignites as soon as the missile leaves the silo-this motor helps clear the missile from water-main motor fires only when the missile has cleared water.The reason why there is an underwater motor is simply because the gas generator in the silo doesnt have enough thrust to propel the missile for 30m underwater.
Take for example, India's "No First Use" policy. It holds more value in terms of morality and public/international relations rather than practical nuclear exchange. If, God forbid, both countries came close to a nuclear war, India's SFC will actually prefer to launch a pre-emptive strike rather than wait for Pakistan's SFC to blow them to Kingdom Come (which they WILL do if it all came down to it).
My friend,I confess,i am not a student of geo politics or nuclear doctrines etc,however i can say with a fairly high degree of certainity based on my
(a) Interaction
(b) Experience
(c) Reading of indian doctrine by prominent members who shaped it in early years
that india sticks to NFUP.it was this entrenched belief in NFUP that even BJP govt decided not to touch it when they came to power with absolute majority in lok sabha.So doubting india's adherence to NFUP is clearly not justified my dear friend! India even in worst case senario- will use nukes only as a counter.Now you would naturally ask- how can i be so sure?Well my answer to that fundamental question is i have access(just like a lot of indians) to some of the very awesome books written on indian nuclear doctrine by some of those who shaped it at one time or another.
Similarly the ever-so-repeated stance of "Massive and Disproportional Response" has little to do with a practical nuclear exchange. Escalatory exchange is always proportional, otherwise you risk the hope of the conflict to resolve at some stage. Just because Pakistan smoked an armored formation settled occupying a bit of Pakistani territory, Indian SFC won't break all hell loose. Because the Pakistani response WILL come after that, and India simple cannot risk its survival. However, taking out the base/missile group/military formation from which the TEL came, is a proportionate response, to which similarly Pakistan won't break all hell loose. Thats how nuclear exchanges would work.
Well i am sure that is the reason why indian govt has invested heavily in ABM program- because they know it pretty well that a full fledged nuclear attack on pakistan would inevitably invite a similar response from pakistan and to blunt that they are working on phase-2 of the program with even better interceptors.Till now more than $2bn have gone into the r&d of ABM program alone and that comprises of extremely long range radars,interceptors etc.I am sure you would acknowledge $2bn isnt a small amount invested in any "one" program.
So when shyam saran says that indian response will be massive against any tactical or strategic nuclear attack then he very well means it!
Look, amardeep mishra, I respect your adherence to logic and published research work. But please, for the love of God, try to understand how the Pakistani military-industrial complex works. We DON'T care for solving problems for showing it to the world. We care for our specific needs, and problems being solved by hook or by crook. If we can't do something ourselves, we buy the solution from elsewhere and replicate the process in-house. So the next time you wonder how Pakistan made the 3D Carbon-Carbon Reinforced Re-entry Nose Tips for its Shaheen series, just don't think that we actually invented it.
However, there are capable & hardworking scientists and engineers having qualifications from abroad sitting in these organizations and working on advanced systems. They face the same problems, have a lot of (unheard) failures, and eventually overcome them.
Well,my friend,let me render you a different angle to this whole design affair-
lets say you decide to design a new rocket(or for that matter any defence system) one day- what would you essentially require?You would require-
1)propellant
2)the casing-interestingly the thickness of casing or missile body is directly contingent upon the chamber pressure and amount of propellants
3)some sort of guidance and control.
Now also suppose the local industry in your country isnt really matured enough to supply any of the 3,then what would you do?You would try to get some of the components from foreign vendors right?But buying has it's limitations!
In pakistans case-lets imagine for a second that china transfered the process by which they create HTPB+AP for their IRBMs to pakistan and pakistan started producing the high energy materials for missiles.
lets also assume that maraging steel required for the missile structure too was obtained from generous uncle wang(or they might have set up a complete plant to manufacture maraging steel for missiles).Lets also assume that control and guidance systems- notably the sensors and actuators too came from china(because the manufacturing of sensors require FABs and is inherently a costly affair).
Everything is working absolutely fine and pakistan has a deterrence against arch enemy india. But india just tested their A-5 and K-4 and are working on A-6 and K-5- now that is a big worry for folks at GHQ PINDI!So they decided to have a similar weapon in their arsenal too!
Now how would you deal with such a scenario?
Because to design a better system you would need RESEARCH at your home country.For instance lets say you wish to replace the truss structure with shroud and external control surfaces with TVC and RCS in order to enable it to fit inside a canister. Now what will be the choice of your TVC and RCS?because TVC provides pitch and yaw corrections and RCS your roll corrections.believe me designing RCS is a pain in the *** job especially for under water strategic missiles- for their is strict limitation on the kind of materials you are allowed to use and their location! It would come to you as a surprise that soviets tried titanium alloys in their RCS of various SLBMs like R-29s etc and failed- they eventually settled with maraging steel and PC steel etc.
Now coming to most important part- composites- without a proper research background in metallurgy and material sciences it will be impossible to find a substitute for maraging steel in missiles because the composite need to be able to bear both temperature and chamber pressure and you would know that in strategic missiles with diameter close to ~2m the radial stresses are way too strong. How would pakistan deal with these situations!
oh and btw i have a question- and that is where do they perform wind tunnel tests of pakistani strategic missiles for
(1) assessing wind flow profile
(2) assessing the stability of missile via assessing the Cx,Cy,Cz coefficients?
How do they mimic the conditions of re-entry?Do they have a plasma wind tunnel lab?
How dumb can people get? This clown seems to be intellectually bankrupt as he hasn't a clue what the heck he's talking about! 
