first of all it's not realistic that ICBM can go anywhere. it just makes european airbases for the americans in cold war essentially worthless. furthermore, it simply adds to realism if you include the possibility to load nukes on subs...
Agreed. The real problem with this issue is that early SSBNs only launched Regulus (1953 - 900km range) or Polaris (1960 - 1800km range).
Not until the 70:s did US Submarines have the capability of launching fully ballistic missiles with 4000+km range.
In any potential cold war scenario during the 50s & 60s this means that Allied SSBNs need to have guaranteed Air-superiority over the waters near the Baltic's or Kola peninsula to get good launchs off against Moscow and other more internal Soviet cities.
No Air Superiority means enemy ASW aircraft and Helicopters get to shoot at your subs as you approach fire range.
I did read a very interesting article suggesting that the US need to have air superiority over the Baltic waters and Swedish territorial water in the 50s and 60s for their SSBNs led to the them influencing Sweden to create a large airforce and large domestic military air-plane industry here. Transferring funds and technology in secret.
From Swedish territorial water US SSBNs would also be in range of all of Soviets largest submarine bases at the time, like Murmansk & Leningrad, even with limited Missile range.
Id also go as far to say that even using 1945 tech it wouldn't be hard to load a nuke onboard a modified submarine and sneak it into a hostile port. Possibly as a desperate suicide attack or with some sort of delay mine mechanism.
Imho Loading of rockets & nukes onboard submarines & ships is crucial for any game to work in a Cold war scenario.