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There is a select group within the Canadian Armed Forces who have received a certificate at the end of their tour of operations in North Bay, Ont., inducting them into the Brotherhood of Underground Mushroomers.

It was an in-joke among those who kept a vigilant eye on Canada’s skies during the Cold War, spending all their working hours in a secret complex deep in the ground where daylight never shone.

“We called it the Hole. When you did a tour there you received a pin and certificate with a mushroom drawn on it,” said Master Corporal Allan Silk who volunteers at the Canadian Forces Museum of Aerospace Defence at Canadian Forces Base North Bay, 350 kilometres north of Toronto.

The Hole, as Silk called it, housed two buildings inside a 5½-storey high cave. You could get to the buildings by North Tunnel from the air base or by the South Tunnel from the city. The complex was behind three 19-ton steel doors which were normally kept open but could be shut during an emergency. “Yet they were so well balanced a five-year-old child could move them with her fingers,” said Silk.

“You had everything you needed there. There was a barber shop, a gym, cafeteria, and doctors’ offices. We assumed that if we had to stay there we could go three weeks or more without needing supplies,” said Marshall Swartz of Bracebridge, Ont., who was stationed at the underground complex three times.

The complex also had all it needed for running a war—a command post, intelligence centre, briefing rooms and a telephone network. It used civilian hydro electricity but had two banks of batteries to provide electricity in case of a power failure. They were backed up by generators that could run on diesel or natural gas.

“We had a reservoir down there for cooling the equipment and the air. We called that our lake. We had a navy too; it was a row boat,” said Swartz.

The aerospace defence museum takes the visitor from the early days to the Cold War. The two main antagonists in a possible nuclear war were the United States and the U.S.S.R. The closest route between the two was over the North Pole and if they were going to clash, it would most likely be in Canadian airspace. There was no room for neutrality and strong trade and a shared continent put Canada in the U.S. camp.

The mood of the times is captured with preserved publications from the period such as an issue of Life Magazine blaring the headline, “How you can survive fallout” and brochures showing how to build a nuclear shelter in your backyard.

In the early 1950s, the Royal Canadian Air Force established the Ground Observer Corps across Canada. Much like the Aircraft Detection Corps in the Second World War, this was a group of 50,000 volunteers, many of them housewives, farmers, lumbermen and fishermen who watched the skies with binoculars and reported aircraft sightings by telephone to filter centres (The Plane Spotters, May/June 2013).

The filter centres were set up across the country commanded by air force officers with a combination of paid and volunteer staff. They would try to identify the aircraft and if unable to do so, alert a radar station which would scramble fighter aircraft to intercept the target or shoot it down. Still, by the mid-1950s, these “eyeball reports” were obsolete and unreliable if an attack occurred at night or in bad weather.

In 1957 Canada and the U.S. formally created the North American Air Defence Command, or Norad, later called the North American Aerospace Command.

The task of identifying aircraft in North American airspace fell to the men and women using the new SAGE computerized system, analysing information from the three radar lines, the Pinetree, the Mid-Canada and the Distant Early Warning lines.

The SAGE (Semi-Automatic Ground Environment) system was complex and large. Most of all, it had to operate out of a secure facility. After a Canada-wide survey was conducted, North Bay was selected to house the facility in part because there already was an air force base, eliminating the need to build one. As well, North Bay was a rail, highway and telecommunications crossroads and nearby Trout Lake offered all the water needed to cool the complex.

But the most impressive credential to the selection committee was its geology. Here was a 2.6 billion-year-old rock formation of granite, one of the hardest rocks on the planet. They could build an underground complex 60 storeys beneath the surface, capable, it was believed, of withstanding a four-megaton nuclear blast which would be 260 times more powerful than the atomic bomb dropped on Hiroshima.

The construction of the Underground Complex (UGC) took four years—one and half years just to excavate and two and a half to build and outfit. One of the prize exhibits in the museum is a chunk of solid rock which looks like a mushroom that was excavated during the building. It is kept by the display for the Brotherhood of Underground Mushroomers.

The UGC cost was $51 million of which Canada paid one third and the U.S. paid the rest. It always had a Canadian in charge and a U.S. officer as second-in-command, mirroring Norad headquarters in Colorado which is overseen by an American general with a Canadian lieutenant-general as his deputy.

Canadian and American military personnel started working in the complex Oct. 1, 1963, and continued 24 hours a day, seven days a week until October 2006. “This was all underground,” said Mel Cannell, a retired lieutenant-colonel in Regina who was stationed there four times. “If you were claustrophobic at all you would go out of your mind.”

There was a bus which came down the tunnel to pick up workers and drive them to the entrance. Cannell remembers one night waiting for his ride at about 9:00 p.m. when suddenly there were no lights.

“I could hear water running down into the tunnel. There had been one hell of a storm outside and the municipal power had gone off,” said Cannell. “For five or 10 minutes everything was black as can be. I remember thinking, ‘Where is the wall?’”

The auxiliary power did come back on and a vehicle came down to pick him up. But for a moment, Cannell couldn’t help wondering if this was the attack.

“We believed that an attack could happen at any time,” said Cannell. “They had to keep you on edge. The controllers were monitored more than normal. They had to take exams every month.”

The SAGE computer system consisted of two huge computers nicknamed Bonnie and Clyde taking up 11,900 square feet. Everything that flew in the northern Norad region had to be identified in two minutes. If not, fighter aircraft, kept fully fuelled and fully armed, were scrambled. The aircraft and the pilots were stationed in a Quick Reaction Alert hangar at the end of the runways. They were expected to be airborne in five minutes.

From the 1950s into the 1990s, the military base was the largest employer in North Bay which today has a population of about 53,000. “I loved the city. It was a great place to raise children,” said Cannell. “There was fishing in the lake and water skiing. We belonged to all the clubs. We didn’t miss out on rock ’n’ roll.”

Among the artifacts in the museum is an unarmed Bomarc missile. Between 1961 and 1972, 446 Surface-to-Air Missile Squadron operated about five kilometres north of the city. In Quebec, 447 Surface-to-Air Squadron operated out of La Macaza, northwest of Montreal.

After much parliamentary debate, nuclear warheads were finally allowed into Canada. As John Clearwater writes in his 1998 book, Canadian Nuclear Weapons: The Untold Story of Canada’s Cold War Arsenal, it was hardly done without notice. Seven nuclear warheads arrived on a United States Air Force transport aircraft and unloaded at 10:00 p.m., New Year’s Eve 1963. “Three trucks marked ‘Explosives’ went from the airfield to the Bomarc site, and one stopped at the ordnance building for unloading. The remaining two trucks moved to the shelter area to deliver the warheads directly to the launchers. The next morning [Minister of Defence] Paul Hellyer would announce the warheads delivered that night had been installed on the Bomarcs upon arrival.”

The warheads remained under the guard of the American forces. Both nations held a key that would arm and launch the weapons if needed. “The keys needed to be inserted into the launch equipment at the same time and the use had to have the authorization of the president of the United States and the prime minister of Canada,” explained Silk.

The SAGE computers were eventually replaced by the Regional Operation Control Centre (ROCC). It was a more versatile system that was substantially smaller than SAGE. It only took up floor space equal to about two houses.

The Bomarcs, too, were becoming obsolete as the Americans created their intercontinental ballistic missiles and the Soviets modernized their weapons systems. In August 1971, Defence Minister Donald Macdonald announced the missiles would be phased out and the nuclear warheads would be returned to the United States.

Canada’s External Affairs Department negotiated with their American counterparts deciding that the two Canadian air force squadrons would stand down as of March 31, 1972. “With much less fanfare and press coverage than their arrival over eight years before, the warheads from the 56 Bomarc surface-to-air missiles were removed and shipped back to the United States in the spring of 1972,” writes Clearwater.

Plans to replace the Underground Complex started in the 1990s. Its computer and communications systems were no longer state-of-the-art and the cost of running such a large facility underground was becoming uncontrollable.

A new above-ground building was built and on Oct. 26, 2006, Colonel Rick Pitre, the base commander, led a symbolic parade of complex staff out of the UGC for the last time. During its 43 years of operation, about 17,000 Canadian and U.S. military personnel had worked there.

The Hole is still there but all the equipment and furniture has been taken out. All that remains are the cooling and ventilating systems that only maintenance workers are allowed to visit.

A colourful movie poster hangs on the wall of the museum’s office. It is for the 2013 Canadian-made science fiction film, The Colony, starring Laurence Fishburne and Bill Paxton with a supporting cast of Canadian actors. Telling the story of survivors of a future Ice Age, the movie was filmed in the Hole. However, there are no plans to use the Hole as a movie set again. Instead the government hopes to find a new use for the space, perhaps as a storage facility for archives.

The days of the Brotherhood of the Underground Mushroomers may be over but their work in North Bay continues. Today, the controllers have a new tool, the Canadian Sapphire satellite. “Where we used to use technology just to look down on our air space, we are now using the space technology to look out into space and watch for space junk,” explained Silk.

Even with the Cold War, the Bomarc missiles and the Hole gone, current history tells us vigilance over our skies is still necessary.