I think it's a question of numbers: if you're building a bunch of new ones and keeping the old ones, your absolute number of deployed weapons goes up, and raise

I think it's a question of numbers: if you're building a bunch of new ones and keeping the old ones, your absolute number of deployed weapons goes up, and raises tensions. But if you build a bunch of new ones and simultaneous retire, and remove from service, a bunch of old ones, so that your deployed number is the same, that shouldn't raise tensions at all. It's hard to imagine how other nations could object to "we're replacing a bunch of old and possibly dangerous weapons with new ones that are much safer so we don't have to worry about having a horrible accident".