Why was there a gamma ray detector?
“Most sites included Gamma detectors that were designed to detect the radiation wave as well. They were redundant systems, any detection, overpressure or Gamma would button-up the site at which point signals were sent to all Continental U.S. sites that a blast was detected, where it was, the size of the blast and wind speed and direction. Sites within 250 miles of any detection would go to Auto-Lock down.”
Bunkers have different grading in terms of blast resistance and most of the AT&T bunkers were engineered for something like 5, 10, 15, or 20 mile air burst strikes of certain warhead yield.
The AT&T bunkers are mostly far removed from population centers such that a direct nuclear strike would be a waste of a perfectly good nuke. In reality, a directly targeted conventional warhead or sabotage would be plenty effective in causing major service disruption so I think a lot of the realities for survivability would be aftermath repair capabilities.