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Buried deep beneath thousands of feet of granite in Colorado is one of the most famous military installations ever built.
Designed during the Cold War to remain operational during a nuclear attack, it features massive blast doors, buildings mounted on giant springs, and systems built to withstand catastrophe.
It has inspired movies, television shows, conspiracy theories, and decades of speculation about what really happens inside.
Learn more about the remarkable history of the Cheyenne Mountain Complex on this episode of Everything Everywhere Daily.
Few military installations are as recognizable, or as misunderstood, as the Cheyenne Mountain Complex outside Colorado Springs, Colorado. Built at the height of the Cold War, it was designed to keep the command structure responsible for defending North America functioning during a nuclear attack.
The origins of the complex lie in the rapid development of nuclear weapons and long-range bombers after World War II.
During the early 1950s, the principal American fear was that Soviet strategic bombers would fly across the Arctic and attack cities and military installations in Canada and the United States.
In response, the US and Canada constructed increasingly sophisticated radar networks across the northern portions of the continent, including the Pinetree Line, the Mid-Canada Line, and, eventually, the Distant Early Warning Line.
The information from these systems had to be collected somewhere, analyzed rapidly, and passed to interceptor aircraft, missile batteries, and national political leaders.
The Continental Air Defense Command was established in Colorado Springs in 1954. In 1957, the United States and Canada established the North American Air Defense Command, or NORAD, formally confirmed by treaty the following year. NORAD centralized the operational control of continental air defenses against Soviet attack.
The original command facilities were above ground at Ent Air Force Base in Colorado Springs. That presented an obvious problem. A command center responsible for managing the defense of an entire continent was itself vulnerable to the very weapons it was supposed to warn against.
Even worse, the threat was changing.
By the late 1950s, the Soviet Union was developing intercontinental ballistic missiles. Sputnik’s launch in October 1957 demonstrated that the Soviet Union possessed rockets powerful enough to place payloads into orbit, which also suggested the ability to deliver nuclear warheads across intercontinental distances.
A command center might therefore receive only minutes of warning.
The obvious solution was to put it underground.
General Earle E. Partridge, commander of Continental Air Defense Command and an important figure in the early development of NORAD, argued that the command center should be separated from other major military targets and hardened sufficiently to continue functioning after a nuclear explosion.
Early planning envisioned a facility capable of surviving blast pressures on the order of 200 pounds per square inch. It would also need independent communications, electricity, water and air-handling systems.
By 1958, NORAD concluded that a command center inside a granite mountain near Colorado Springs offered the best combination of protection, expansion capability, communications access, and cost.
Cheyenne Mountain was not simply selected because it happened to be nearby.
Several possible locations around Colorado Springs were examined, including Blodgett Peak near the Air Force Academy. The Army Corps of Engineers ultimately recommended Cheyenne Mountain, and the Joint Chiefs of Staff approved the location in March 1959.
There were several advantages.
First was geology. Cheyenne Mountain consists largely of extremely solid granite. Granite provides an enormous natural shield against blast effects, heat, radiation, and flying debris. Instead of constructing thousands of feet of reinforced concrete, engineers could use the mountain itself as armor.
The mountain also allowed chambers to be excavated deep enough that roughly 1,500 to 2,000 feet of rock could lie between portions of the facility and the surface.
Second was location. Colorado Springs was already the center of North American air-defense command operations. Moving NORAD hundreds or thousands of miles elsewhere would have meant recreating an extensive communications and support network.
Third was isolation. In the late 1950s, the area surrounding Cheyenne Mountain was sparsely populated compared with most American cities. It was also sufficiently separated from other high-value military installations such that a single Soviet weapon would be less likely to destroy multiple facilities simultaneously.
There was also another advantage that became increasingly important: room for expansion.
NORAD argued that an underground complex excavated in granite could be enlarged more readily than a conventional hardened structure built with concrete.
Funding and bureaucratic debates delayed construction for several years. By the fall of 1959, the Air Force had selected Cheyenne Mountain and obtained initial funding, but the Office of the Secretary of Defense temporarily froze much of the money while defense plans were reassessed.
The project finally received renewed approval in 1961.
The Utah Construction and Mining Company received the excavation contract and worked under the supervision of the U.S. Army Corps of Engineers. Initial excavation began in May 1961, followed by a ceremonial groundbreaking in June involving NORAD commander General Laurence Kuter and the head of Air Defense Command General Robert M. Lee.
The scale of the project was enormous.
Miners drove large tunnels directly into the granite using controlled explosives. One important innovation was a technique known as smooth-wall blasting. Instead of simply detonating large charges and fracturing large areas of surrounding rock, engineers carefully positioned and timed smaller explosions. This produced comparatively smooth excavation surfaces and reduced unwanted cracking.
The main excavation was accomplished remarkably quickly. It was reportedly completed in 367 days.
Ultimately, approximately 693,000 to 700,000 tons of granite were removed, creating about 5.1 acres of underground floor space.
More than 100,000 rock bolts were installed to stabilize the walls and ceilings. Some were dozens of feet long.
Engineers discovered fractures and shear planes in portions of the mountain that had not been apparent during preliminary geological surveys. At one point, the orientation of portions of the complex had to be changed to avoid rock formations that could cause problems.
One particularly troublesome intersection became known as the B-2 intersection. Engineers discovered geological weaknesses in the ceiling that might remain stable under normal circumstances but could fail under the shock of a nuclear explosion.
Their solution was extraordinary. They constructed a massive reinforced-concrete dome underneath the questionable rock, in places several feet thick, which added millions of dollars to the project.
Cheyenne Mountain is sometimes imagined as rooms carved directly into the rock. That is not quite how the main complex works.
Engineers first excavated enormous underground chambers. They then constructed conventional steel buildings inside those chambers.
There are fifteen principal buildings in the complex, generally described as twelve three-story buildings and three two-story buildings.
The truly remarkable feature is that most of those buildings are not rigidly attached to the cavern floor.
They sit on enormous steel coil springs.
Roughly 1,300 springs support the buildings. Each spring is several feet tall and can carry tremendous loads. The idea is similar to shock isolation in machinery, only on the scale of entire buildings.
If a nearby nuclear explosion sent a shock wave through the mountain, the granite itself would move. A building rigidly attached to the rock could suffer catastrophic structural damage or destroy sensitive equipment.
The springs allow the rock and the buildings to move somewhat independently.
Because of the springs, flexible connections were required for water pipes, electrical cables, ventilation ducts and other utilities. Otherwise, the building might survive while all of its pipes and cables snapped.
The most famous pieces of Cheyenne Mountain engineering are its enormous blast doors.
The main entrance tunnel penetrates deeply into the mountain before reaching the protected portions of the facility. The geometry of the tunnels was deliberately designed to prevent a blast wave from traveling directly into the command center.
Two giant steel blast doors can seal the entire complex from the outside.
Accounts vary slightly depending upon the particular door and period, but they weigh roughly 20 to 25 tons each and are about a meter, or approximately three and a half feet, thick.
Despite their enormous mass, the doors are balanced so carefully that they can be shut in just 45 seconds. Because they don’t want pressure differences to hold the doors shut, they are only closed in the event of an actual crisis or a training exercise.
Cheyenne Mountain’s defensive engineering basically works in layers. The mountain absorbs much of the initial blast. Tunnel geometry dissipates additional energy. Blast doors seal vulnerable openings. Springs isolate buildings from shock. Filters and valves protect against radioactive or chemically contaminated air.
The NORAD Combat Operations Center began operating inside the mountain on April 20, 1966. Additional systems were installed afterward, and official histories also cite February 6, 1967, as the date of completion or full operation of the complex.
The total reported construction cost was approximately $142.4 million in 1960s dollars, an enormous investment at the time.
Through the late 1960s, 1970s and 1980s, Cheyenne Mountain became increasingly associated with missile warning rather than simply bomber defense.
Satellites and ground-based radars could detect missile launches and track objects in space. Information flowed into computers inside the mountain, where personnel attempted to determine whether an apparent launch represented an attack, a test, a satellite launch or an error.
The complex became an integral part of the system connecting NORAD, Strategic Air Command, the Pentagon and national command authorities.
That responsibility produced some frightening episodes.
On November 9, 1979, test data representing a Soviet nuclear attack were accidentally fed into the operational warning system. Displays indicated that large numbers of Soviet missiles were headed toward North America.
Military aircraft and command posts reacted before other sensors revealed that no missiles existed.
Then, on June 3 and June 6, 1980, another series of false warnings occurred. A faulty electronic component inserted incorrect numbers into warning messages, at times making computer displays appear to show a large Soviet missile attack.
The terrorist attacks of September 11, 2001, presented Cheyenne Mountain with a completely different problem.
NORAD had spent decades preparing primarily for attacks arriving from outside North America. The hijacked airliners of 9/11 were ordinary domestic aircraft turned into weapons from inside American airspace.
Personnel inside Cheyenne Mountain suddenly had to help coordinate fighter responses to an unprecedented internal attack while the Federal Aviation Administration attempted to identify and ground thousands of civilian aircraft.
The mountain’s massive blast doors were closed during the crisis.
NORAD personnel have described September 11 as the only real-world contingency in the facility’s history in which the doors were sealed.
Ironically, the post-9/11 era eventually led to a reduction in Cheyenne Mountain’s role as the everyday NORAD command center.
Modern communications allow information from radars, satellites, and other sensors to be displayed virtually anywhere via secure connections. Being buried inside a mountain also had disadvantages.
Space was limited. Expanding offices was difficult. Workers had to travel through security and tunnels simply to reach their workplaces. Maintaining specialized 1960s infrastructure was expensive.
Most importantly, the threat had changed.
The everyday defense of North America increasingly required constant coordination among military commands, intelligence agencies, civilian authorities and emergency-management organizations. An above-ground headquarters at nearby Peterson Air Force Base offered greater flexibility.
In 2006, NORAD and USNORTHCOM commander Admiral Timothy Keating approved moving much of the routine surveillance and warning mission to Peterson.
That led to headlines suggesting that Cheyenne Mountain was being “closed.”
NORAD’s ordinary command operations moved to Peterson, but the mountain continued to operate as a hardened backup command center and to house military communications.
Cheyenne Mountain was a product of one of the most dangerous periods of the Cold War, built on the assumption that the United States might someday have to keep operating after a nuclear attack.
Although its role has changed, the complex has never truly become obsolete. More than sixty years after it was carved into granite, Cheyenne Mountain still serves the purpose for which it was created: providing a protected place from which North America can be defended when everything above ground has gone wrong.