From: Washington D.C.
The essence of deterrence is the ability to hold targets at risk, so it probably wouldn't matter how close they came, they wouldn't necessarily be considered hostile.
Submarines, being more survivable than land based missiles and bombers, are often considered to be a "second strike," weapon. They prevent one side from attacking another by insuring that if they do attack, there will always be enough weapons remaining to deal a devastating counter strike. If you attacked the Russian submarines before they came close enough to attack targets on land with their missiles, that might be considered preparation for an American first strike because they'd be eliminating the Soviet's ability to respond. That forces a first strike by the Soviets because they can't sit around and wait for their ability to counter strike to be eliminated. Therefore, you'd never attack the SSBNs just because they were in range of their targets.
More likely they'd keep an eye on them somehow and monitor them for signs that they might be preparing to launch. They'd only attack if it looked like a nuclear attack was imminent. That's the whole purpose of "track and trail," like you read about in Cold War histories. You wanted to secretly know where the SSBNs were at all times, so that in the event of signs of an imminent launch, you could destroy them quickly without seeming threatening.
The situation is always unstable, hence the need to play it cool on both sides. Both sides specifically did not want to be the first to start shooting because the first shot, even if it was conventional, could be perceived as the preparation for all-out nuclear war (something to be avoided). That's why deterrence works. Winning means shooting never happens.
What I would do to make a complicated Cold War scenario, is have some very small probability (like... 1 in 10 for "fun's" sake) of changing the side postures to "hostile." Most of the time they'd merely be "unfriendly." Victory would consist of your side's defended aim points remaining intact. Most of the time nothing happens, but you still have to find all the enemy SSBNs because in the event that something actually does occur, you need to be able to destroy them quickly before they launch and limit the damage.
I'm knee deep designing a Cold War scenario in which Soviet boomers are encroaching the East Coast of the US, approximately 600-700 NM from the coast and in international waters. I'm curious on real world doctrine and RoE for the era (1967) on how close subs with ICBM's (SS-N-5 Stark with a 750 NM range) would be allowed to approach before being considered hostile and engaged.
< Message edited by SeaQueen -- 10/25/2016 7:15:34 PM >