The question is not about PN's capabilities but rather neutralizing their main strike before it happened. That is what I disagreed with sfhussain for.
The fact of the matter is we should bet on assumptions we can take out their main strike before it happens or that their main strike will only be 10% of what their actual weapon size is as we will be able to eliminate rest.
As for PN's capabilities it has been floating around for quite sometimes now that Babur can be launched from PN ships thus giving Pakistan the capabilities to attack from sea as well but the question would remain can we fire it from Subs to give us the second strike capability.
Though if nasr can be fired from ships it will give us the tactical strike capability to knock out their attempted blockade of Karachi or other ports.
Indians have a very very limited and rudimentary capability through acquisition of three Israeli built Green Pine radars to identify those Pakistani missiles fired within their acquisition range. But their Ballistic Missile Defence at best is in its early stages of development and will not be able to do anything with regard to a Pakistani nuclear attack. Same is the case with regard to Pakistani system. I really wonder if the Americans or even the Israelis also have a completely fool proof system which could counter a Pakistani nuclear armed ballistic missile attack - in fact they don't.
Therefore, in case of current India Pakistan environment, it does not matter if the nuclear armed missiles come from the sea or are land based. These will hit their targets irrespective.
Pakistan may be able to identify movement of Indian nuclear submarine. But when this submarine fires its nuclear armed ballistic missiles, Pakistan may not be able to do much. Pakistan can however, pre-empt and attempt to destroy the Indian nuclear submarine under hostile environment, if it can detect it and if it enters a zone where Pakistani targets fall within its ballistic missile carrying ranges. Pakistan can do this by firing its conventional anti submarine missiles or can even use a nuclear weapon to destry this nuclear submarine.
One however, need to understand that the submarines are launched much before breakout of hostilities and a nuclear submarine can hide itself much much longer underwater as compared to a conventional submarine. Therefore, the need to identify all the nuclear armed submarines the moment they leave their home port and the need for a continuos tracking of their movement.