During the cold war, Soviet forces attacking the USA would have to cross Canada, the most critical part of North America's defense. Therefore North Bay's UnderGround Complex (UGC) was constructed. It was the only subterranean NORAD facility (1963-2006) able to withstand a nuclear strike.
When NORAD was set up another site was added at CFB North Bay in Canada, although in this case the entire Semi-Automatic Ground Environment system (radar detection) http://i.imgur.com/kVs1GqD.jpg was buried approximately 700 feet underground in what became known as "the hole". Buried within 2-billion-year-old granite of the the Canadian shield was the Canadian (and most critical) portion of NORAD (North American Aerospace Defense Command). Along with Cheyenne Mountain in the USA, they provided airspace warning, air sovereignty and defense for both countries.
Entry to 'The Hole' was by driving through a 2km long tunnel until a mammoth door that was so well balanced, even thought it weighed tons, it could be swung open by a child. "The Hole" was a stadium-sized cavern that could generate its own power and filtered air for a month and had storage for more than 5 million gallons of water. The facility operated for 43 years until moving to an above-ground building at grid 46°21'25"N 79°24'56"W in 2006. (SEE: CFB North Bay)
SAGE mountain North Bay. Main (north) tunnel entry at grid 46°21'22"N 79°25'1"W http://storage.nugget.ca/v1/dynamic_resize/sws_path/suns-prod-images/1297474081934_ORIGINAL.jpg?quality=80&size=650x&stmp=1380667491365 Personnel marching out at closure.
Secondary (south) entry at grid 46°19'48"N 79°24'41"W http://storage.nugget.ca/v1/dynamic_resize/sws_path/suns-prod-images/-430294_ORIGINAL.jpg?quality=80&size=650x&stmp=1342677835150
video footage http://www.youtube.com/watch?v=HRvPPnHMsyE
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