It's my understanding that during the cold war US nuclear subs filled pretty much the same purpose: last-strike capability that could not be taken out by a succ

It's my understanding that during the cold war US nuclear subs filled pretty much the same purpose: last-strike capability that could not be taken out by a successful first-strike by an adversary hitting the US's ground-based launch facilities. IIRC bombers were part of this strategy as well but presented easier targets to take out. It's just that the launch decision authority was delegated to a large decentralized group of commanders with ever lower ranked officers automatically receiving that authority if higher level officers were taken out or rendered incommunicado due to the fog of war or wide scale decapitation strike.