I don't know but I doubt we are increasing capacity. At one point the arsenals were so high the whole planet could be devastated mulitple times between the various countries. The article talks about extension of the last model and this is just finished as the modernized version. So I think its likely just going to replace as they decommission. They just want to keep up the various deterents. Sub missiles, ground missiles, and air bombs. The air and sub is mainly so the other side relizes even if they wiped out the land retaliation was possible. Not sure if they still do it but they used to have at least one nuclear armed aircraft in the air and sub at sea with enough fuel to get anywhere and I believe several but of course you have ones leaving and coming back so there is overlap.