The Pentagon is moving the headquarters for the North American Aerospace Defense Command (Norad) back into Cheyenne Mountain near Colorado Springs, Colo., a decade after having largely vacated the site.

Why the return? Because the enormous bunker in the hollowed-out mountain, built to survive a Cold War-era nuclear conflict, can also resist an electromagnetic-pulse attack, or EMP. America’s military planners recognize the growing threat from an EMP attack by bad actors around the world, in particular North Korea and Iran.

An EMP strike, most likely from the detonation of a nuclear weapon in space, would destroy unprotected military and civilian electronics nationwide, blacking out the electric grid and other critical infrastructure for months or years. The staggering human cost of such a catastrophic attack is not difficult to imagine.

The primary headquarters for Norad, which provides early warning and command and control for the defense of the U.S. against nuclear attack, has for a decade been at nearby Peterson Air Force Base. Critical Norad operations are being moved back into Cheyenne Mountain, and the Pentagon recently awarded a $700 million contract to Raytheon to upgrade electronics through 2020.

At an April 7 Pentagon news conference, Norad Commander Adm. William Gortney noted that Norad is going back underground “because of the very nature of the way that Cheyenne Mountain’s built. It’s EMP-hardened.” He explained that North Korea now has mobile intercontinental ballistic missiles, the KN-08, armed with nuclear warheads, that can strike the U.S. While the KN-08 is inaccurate, it could be used to launch a high-altitude nuclear EMP attack.