There's some debate about whether Perimeter was ever deployed, or rejected after some design phases. Also, its reliance on siloed ICBMs to launch communications

There's some debate about whether Perimeter was ever deployed, or rejected after some design phases. Also, its reliance on siloed ICBMs to launch communications warheads causes a problem; you have to intermix them with normal missile silos (or they get preferential targeting). And those normal missile silos are also the classic first strike targets.