COLORADO SPRINGS, CO—Across the highway from the US Air Force Academy is a tiny cluster of buildings that represents one of Colorado Springs' earliest claims to fame: mining.

The Western Museum of Mining and Industry (WMMI) looks out onto a glorious expanse of the Rocky Mountains and is home to all manner of antique equipment that extracted minerals from those mountains.

But on a balmy April night, as a spring snowstorm rolled in from the west, Ars attended a lecture at the museum about a nearby mining marvel that was not intended to extract riches, but to bury something more valuable beneath the unyielding rock—knowledge.

The US military commissioned a bunker to be built in Cheyenne Mountain outside of Colorado Springs at the height of the Cold War in 1961. The bunker captured the public’s imagination and inspiring the 1983 movie WarGames, as well as the 2015 Terminator reboot Terminator Genisys. In real life, the Cheyenne Mountain Complex currently houses divisions of the North American Aerospace Defense Command (popularly known as NORAD), US Strategic Command (USSTRATCOM), US Northern Command, and the US Air Force Space Command. Their objectives are to watch the skies for hostile entities and to analyze air and space traffic.

While we would have loved to step inside Cheyenne Mountain ourselves, tours for civilians are hard to come by these days. According to NORAD's Facebook page, groups wishing to tour the complex must have a "mission-critical" reason to do so. While we consider every Ars Technica article mission-critical, the US military's definition of that term varies somewhat from our own. So an exhibit at the nearby mining museum and a lecture from James Crews, a former Cheyenne Mountain Director of Staff, would have to do.

Megan Geuss

Megan Geuss

Megan Geuss

Megan Geuss

Megan Geuss

Megan Geuss

Megan Geuss

Special Collections Department, Stewart Library, Weber State University

Megan Geuss

Megan Geuss

Megan Geuss

Department of Defense

Department of Defense, J. Carol Floyd

Department of Defense

Department of Defense

Department of Defense

Department of Defense

Department of Defense

Moving mountains

In the early ’60s, San Francisco’s Utah Construction and Mining Company won the contract to build the nuclear bomb-resistant bunker. A museum exhibit describes how blasting the rock more or less indiscriminately would have produced jags and fissures in the rock. Instead, according to the exhibit, Utah Mining introduced a new method of excavation that involved blasting precisely measured explosives in concentric rounds of detonations at just the right time. It took only three months to clear the main tunnel, which curves to deflect blast waves from missiles or nuclear explosions.

Once the tunnel was cleared, Utah Mining found sheers in the rock that would have weakened the structural integrity of the bunker. To mitigate the ill effects of the rock formation, the blueprints of the complex were altered to push the bulk of the complex askew from the main tunnel.

Crews gave WMMI patrons a quick rundown of some of the facts and figures pertaining to NORAD and the other military agencies housed in Cheyenne Mountain. Crews said that, contrary to popular belief, the US military never initially designed Cheyenne Mountain to withstand a direct nuclear missile strike. “They were planning for aircraft strikes,” Crews said. “Cheyenne Mountain was never designed to be a direct hit. It was always designed for a near miss or a hit from about 10 miles.”

But the bunker was strengthened as it was built, and Crews said that today Cheyenne Mountain is "still the best protected system that we have in the United States.”

After excavating tunnels, Utah Mining reinforced the bunker with a series of 6ft- to 25ft-long rock bolts and steel ribs at tunnel entrances to hold the rock together at up to 10,000 lbs of force. In many places, rock is covered by metal mesh to keep it from cracking and falling. The price-tag for these structures was considerable—according to the WMMI, mining the space for the underground fortress was only 10 percent of the cost of building Cheyenne Mountain.

Cheyenne Mountain can seal itself off from the world if it has to. Air, water, and power all enter the facility through protected channels, so if there’s an attack on US soil the staff inside the complex can close off two 3.5-ft, 25-ton steel blast doors. (In fact, Cheyenne Mountain lucked out when it came to a water source: an underground spring was unexpectedly found beneath the mountain during excavation.) Throughout the Cold War, one of the two doors was always shut, and personnel changing shifts had to wait for the doors to cycle open. “Last time the blast doors closed was in 1991 in December, that was the formal ending of the cold war,” Crews said. “The only time they’ve ever been closed in anger since then was on 9/11.”

NORAD was the military entity that gave the orders to ground all flights over North America on September 11.

The power, air conditioning, water, and computer systems in the Cheyenne Mountain complex all have three levels of redundancy. Under normal conditions, the bunker draws power from the nearby utility. But if that fails, Cheyenne Mountain has a number of diesel generators built for high altitude operation. If those fail, a system of batteries can keep the complex running for a while longer.

“The warners cannot be the trigger pullers”

In describing how various military divisions currently operate inside Cheyenne Mountain, Crews mentioned that NORAD is actually a bi-national command shared with Canada. At any given time, about 20 percent of the bunker's NORAD staff is Canadian. Together, US and Canadian forces track objects in both North American airspace and in orbit.

Cheyenne Mountain has no antennas. "Those would get blown off very readily" in an attack, Crews joked. When pressed about the fiber optics that feed the bunker, he limited his response to "There's no other place in the world that has communications like Cheyenne Mountain."

The staff at Cheyenne Mountain gets its information from myriad sources. "There’s probably 300 people feeding information to these seven or eight stations here, from intel, radar," Crews said. "The air battle management officer is in charge of scrambling aircraft—he gets information from the air warning center."

The agencies inside Cheyenne Mountain also use predictive software to track aircraft that go off course. The software quickly determines how long it would take the errant craft to reach any potential targets in its vicinity.

Cheyenne Mountain used to train its staff on shuttle missions run by NASA. "Shuttle missions, we treat those as hostile," Crews said. "We test the people, we test the systems, we get on-the-job training like you wouldn’t believe."

In the event of a real attack, NORAD detects missiles by satellite and by radar (this is called "dual phenomenology"). Contrary to Hollywood, NORAD can't launch a missile against a target in defense. "The warners cannot be the trigger pullers," Crews said. "NORAD only has orders to disperse aircraft, no other dictate."

Listing image by Department of Defense