If the experiments had occurred, the fallout would have altered the landscape of northern Manitoba, drifted southeast toward Montreal and New York and reached as far as Europe's Nordic countries, according to a nuclear arms expert.
The top-secret plan would have seen "about a dozen" nuclear bombs detonated over several years beginning in 1953, according to the 20-page document, entitled The Technical Feasibility of Establishing an Atomic Weapons Proving Ground in the Churchill Area.
It was acquired by John Clearwater, a military analyst and author of three books on nuclear weapons, including a ground-breaking study that showed the Canadian Armed Forces were equipped with nuclear weapons from 1963 to 1984.
The document remained unused and unreported until Clearwater provided a copy to the Free Press.
A former Winnipegger who lives in Ottawa, he served as an adviser to the government of the United Arab Emirates last year.
Clearwater said the British were looking for a place to test their first nuclear bomb, dubbed the Blue Danube, a 25-kiloton weapon slightly larger than the ones dropped on Nagasaki and Hiroshima in 1945 at the end of the Second World War.
Those bombs killed 110,000 people and injured 130,000. By 1950, another 230,000 people had died from injuries or radiation.
The plan also envisioned the United States using the proving ground, which would have increased the number of nuclear detonations in the Churchill area.
Clearwater said the British ultimately decided to conduct their tests in Australia, possibly because Churchill was considered too cold and uncomfortable for the hundreds of scientists who would have worked on the project.
"Thank God for that," Churchill Mayor Mike Spence said this week. "If those bombs had gone off, it would have changed Churchill today. We are becoming an international tourist destination, and all of that would have been lost.
"They'd have sacrificed the communities up here, the environment, the wildlife, all of that," said Spence, a Cree Indian born in Churchill.
The document identified several places in Canada that could be used for nuclear testing, but the area around Churchill was considered the best.
Ground Zero was to be a site near the mouth of the Broad River, located 100 kilometres southeast of Churchill on Hudson Bay, which is now part of Wapusk National Park.
It was described as an unimportant wasteland, inhabited by only a few trappers and hunters. The area's black spruce, the document said, had "negligible value."
The sub-Arctic terrain near Churchill is especially susceptible to ecological disaster, and nuclear testing would have had long-term negative consequences for the region, Clearwater said.
"The problem in the Far North is that the ice traps the radioactive bits and holds on to them for hundreds of years," he said.
Radiation would have contaminated the moss, lichen, mushrooms and other vegetation in the North and then quickly entered the mammal food chain.
When a nuclear reactor in Chornobyl, Ukraine, failed in 1986, the radiation almost immediately appeared in the reindeer of northern Finland, some 1,600 kilometres from the disaster, he said.
The fallout, carried by wind and rain, contaminated huge areas of Eastern Europe and Scandinavia, causing tonnes of fresh produce and dairy products to be destroyed.
Churchill was a sprawling military base in the 1950s. Some 6,000 Canadian and U.S. soldiers were stationed there, and Canada operated a rocket-testing range at the base until it closed in 1984.
Clearwater said the consideration of Churchill as a nuclear test site has to be understood in the context of the early Cold War.
"The idea of allowing testing of nuclear weapons is hardly that strange when you consider the time and the place," Clearwater said. "Canadians were being conditioned heavily to hate and fear, and the Cold War was now in full swing. Nuclear weapons were presented as the saviours of the free world, and Canada would do what was necessary to guard against Bolshevism. Not necessarily nuclear testing, but nuclear testing if necessary."
Several key events that occurred around the time the secret military plan for Churchill was developed helped fuel the paranoia and hysteria.
Mao Tse-tung's communists took control in China, the Soviets tested their first nuclear bomb, West Berlin was blockaded and war clouds gathered over Korea.
Sacrificing northern Manitoba, part of Australia or the Pacific islands where testing also occurred would have seemed trivial against the backdrop of a world that appeared to be on the brink of another world war.
Some of the Churchill tests would have been conducted from the top of a tower, while others would have involved dropping bombs from an airplane to assess their destructive power and effectiveness, the document reveals.
However, the tests that ultimately took place in Australia were mainly tower and surface bursts, with just one air drop, Clearwater said. Surface bursts create the most fallout, he said.
In language that seems naive and callous today, the document's authors said nuclear explosions near Churchill wouldn't cause any meaningful environmental damage, and there was no one in the area who would care anyway.
"The area is waste land suitable only for hunting and trapping," the document reads. It "is uninhabited except for the occasional hunter or trapper."
The authors also noted that because the prevailing winds came from the north, "no contamination of this inhabited area (Churchill) should result nor will any source of drinking water be affected.
"The slight fallout of contamination south and southeast of the Broad River," the document continued, "will not affect the white whale fishing off the mouth of the Churchill River."
The bureaucrats did acknowledge that some contamination would occur up to 160 kilometres downwind.
The report emphasized the need for secrecy.
"Every effort must be made to keep secret the nature of the trial before the event," it said, adding: "Once detonation has occurred, there will be little hope of keeping secret the fact that an atomic explosion has taken place.
"Some cover name must be invented to explain why men and equipment are being taken into the base, but if the base is a research station, such as Churchill, it seems possible that no special attention will be called to the preparations."
The Town of Churchill, in the 1950s, had a civilian population of just 600, although thousands of soldiers and airmen worked at the nearby military base.
If the nuclear-testing plan had become operational, nearly 400 British scientists, technicians and other workers would have been moved into the base. Even more workers would have been involved if the Americans participated.
The Churchill plan was authored by C.P. McNamara of Canada's Defence Research Board and W.G. Penney, an official in Britain's Ministry of Supply, around 1949, the year the Soviet Union detonated its first N-bomb.
Penney was a scientist who worked on the Manhattan Project, code name for the American atom bomb initiative.
Their elaborate proposal, including detailed plans for roads, barracks and other infrastructure, was never approved by then-prime minister Louis St. Laurent.
However, Clearwater said it is clear that such approval would have been a mere formality if Britain had decided to move forward.
"Since it was a bilateral international report, there had to be a significant level of authority for it to proceed," he said.
The plan would not have been disclosed to anyone in Manitoba and would have been confined to military headquarters in London and Ottawa, Clearwater said.