The trick to submarines is that large enough boats to carry ICBMs require specific ports with specialized docks, and other auxiliary equipment. Every nation with the necessary intelligence capability knows where all of those ports are, for all potential threats. Those ports are watched constantly by satellites to keep track of the boats coming and going, and build profiles on where they might go within a given amount of time.
The trick to submarines is that large enough boats to carry ICBMs require specific ports with specialized docks, and other auxiliary equipment. Every nation with the necessary intelligence capability knows where all of those ports are, for all potential threats. Those ports are watched constantly by satellites to keep track of the boats coming and going, and build profiles on where they might go within a given amount of time.
Could be, but at any given time there are submarines out in the sea submerged at unknown location. And those would launch counterstrike easily.