On This Day: America’s ‘Defence Mountain’ nuclear command post is built underneath the Rockies

FEBRUARY 8, 1966: America’s Cheyenne Mountain fortress – a city built under the Rockies to serve as a nuclear bunker, alert hub and command station – was completed on this day in 1966.

The $142million five-acre compound beneath 2,000ft of granite is designed to absorb a 30megaton bomb and house 800 people for a month in the event of an attack.

The facility, which lies 7,000ft above sea level in Colorado, is now the primary warning centre for all missile, space and air threats to North America.

A 1966 British Pathé newsreel provides an intriguing glimpse inside the headquarters of the North American Aerospace Defense Command (NORAD) at the time.

The then high-tech technology inside the three-mile network of tunnels – nicknamed Defence Mountain – included giant computers operated by large spinning discs.

An analyst is also shown using a special electronic gun and pointing to a spot on a map of North America to see what is in the airspace there.

During the Cold War, it was hoped that this warning centre – run by both U.S. and Canadian personnel - would be able to rapidly alert the military to any threats.

To ensure that 1,200 permanent staff could do their jobs and continue to survive in the case of a nuclear attack, Cheyenne Mountain was built to withstand a major blast.

Inside, 15 buildings – some more than three-stories high – “float” on 1,319 springs that are designed to absorb the shock of an explosion.

The complex, which took four years to build, also has its own impregnable water supply – from a spring inside the mountain – and four storage reservoirs.

[On This Day: U.S troops occupy Okinawa after bloodiest battle of Pacific]

It is powered by an outside source but in case of attack there are giant batteries that can provide 15 minutes of electricity before eight huge diesel generators kick in.

The air supply is also rigorously filtered to ensure no contaminants – especially nuclear ones.

As well as being deep within a mountain, the fortress is also bolstered by two sets of 25-ton steel blast doors.

During the height of the Cold War in the 1960s and 1970s, they were regularly closed for long periods of time.

The last time Cheyenne Mountain was sealed like this was following the September 11 terror attacks in 2001.

Now, as well as looking for threats from outside the U.S. and Canada, they are tasked with thwarting possible attacks from within.

Every year on Christmas Eve NORAD also purports to track Santa Claus as he delivers presents around the world.

[On This Day: Government bans cigarette advertising on TV]

This tradition started in 1955, when children could phone a number to find out where Saint Nick was, and now lets people watch his progress online and with mobile apps.

Cheyenne Mountain’s role was highlighted in the 1983 movie WarGames in which Matthew Broderick stars as hacker who unwittingly almost triggers a nuclear war.

It also houses the command centres of the Air Force Space Command and the U.S. Space Command, which were both created later in the 1980s.