They are nightmare scenarios ripped straight out of Hollywood thrillers.

But rising global tension, notably over North Korea, has prompted federal officials to review and in some cases revise a series of critical contingency plans, including one that involves the evacuation of the federal cabinet to a secure military base outside of Ottawa.

The Privy Council Office, the bureaucratic wing of the Prime Minister's Office, drafted an agreement with National Defence a year ago to open up bunkers on two military bases should the National Capital Region become "unviable," according to documents obtained by CBC News under access to information legislation.

Each location is classified in the heavily redacted briefing dated Aug. 2, 2016, and only referred to as "Alpha and Bravo sites."

The agreement is part of the federal government's overall plan for the "Continuity of Constitutional Government," which aims to "ensure minimal or no interruption to the availability of critical services" during an emergency or natural disaster in Ottawa.

Foreign Affairs Minister Chrystia Freeland joins Chris Hall to discuss Canada’s role in addressing the North Korea nuclear crisis. 8:11

The federal government has long had contingency plans, known internally as CONPLANS, for a variety of emergencies running the gamut between earthquakes and floods through terrorism to full-scale war.

What is different lately, according to experts, is that officials are being forced to think more often in Cold War terms, particularly when it comes to the threat of a North Korean missile striking Canada, either as an accident or by design.

On Tuesday, Pyongyang tested the Hwasong-15 intercontinental missile, which the regime of Kim Jong-un claims can be tipped with a "super-large heavy warhead" and is capable of striking anywhere on the continental United States.

Defence Minister Harjit Sajjan was asked Wednesday what would happen should a missile land in Canada.

"When it comes to any type of foreign threats, we take them extremely seriously," he said. "We've been looking at North Korea right from the beginning when I was given this portfolio. I am very mindful of the country's missile testing that they have been doing. We believe that the diplomatic solution is the way to go, because I think that there is hope for it."

The notion that Canada could be hit by incoming missiles was part of the Cold War defence mindset and planning, which disappeared in the early 1990s, said Andrew Rasiulis, a defence expert with the Canadian Global Affairs Institute.

"After the Cold War was over, we stopped thinking about those things. It fell off the radar, so to speak," said Rasiulis, a former senior official at National Defence who once ran the Directorate of Nuclear and Arms Control Policy. "At the time, it was really a whole cultural shift."

Cold War legacy

At the height of the standoff with the former Soviet Union, the Canadian military had a series of bunkers to which the federal cabinet could retreat, including the so-called Diefenbunker, near Carp, Ont.

There was also the deep underground complex at Canadian Forces Base North Bay and another centre at the now-decommissioned military base in Calgary.

Rasiulis said a whole generation of public servants have not had to think in those cataclysmic terms and had not even begun to consider it as late as 2014 when he retired.

And that's why he considers the revision of continuity of government plan so significant. But Rasiulis said he considers the likelihood of Canada being struck by a North Korean missile to be low.

The thinking, however, over the last generation was, if there was thought of a nuclear event, it would be a terrorist dirty bomb, not a missile or missiles that could wipe out entire cities and result in tens of thousands of casualties.

Although on the surface they may not seem related, Rasiulis said the Russian annexation of Crimea and the lone-wolf, ISIS-inspired terrorist attack on Parliament Hill, both of which occurred three years ago, appear to have convinced officials that the capital was vulnerable.

The main tunnel to the so-called Diefenbunker in Carp, Ont. (Sean Kilpatrick/Canadian Press)

Sean Maloney, a professor at the Royal Military College of Canada and a Cold War expert, said he believes the issue is bigger than just whether there are contingency plans to keep the government operating. He questions what sort of civil preparedness is going on.

A nuclear blast brings with it an electromagnetic pulse that would fry power grids over a much wider area than just the radius of the blast. That, in turn, would take down not only businesses but public infrastructure, such as water and sewage plants.

"That is just the start of the problem," said Maloney. "People have not thought that through and they don't want to discuss it because it's too overwhelming for them."

He said during the Cold War, there was also a sense of "lethargy" because people were resigned to the fact that once the missiles started flying everything would be over.

Maintaining the power elite

Maloney wrote a paper in the late 1990s about the federal government's contingency plans in the event of a thermonuclear war with the Soviet Union.

It was entitled Dr. Strangelove Visits Canada, referring to the 1960s Stanley Kubrick comedy about what could happen if the wrong person pushed the wrong button.

Some of the issues raised in his paper could find new life in this new era of uncertainty.

"Critics of civil defence programs argued that protecting government leaders in shelters and not providing similar facilities to the population as a whole was 'undemocratic,' [and] designed to maintain the power elite," said Maloney who added the current plan to reconstitute the government "sounds very 1950s."

The government of former prime minister John Diefenbaker conducted the first large-scale training exercise for its contingency plan to evacuate Ottawa in December 1959.

It saw one North Star transport plane and one Labrador helicopter put on 30-minute standby to evacuate senior government ministers and officials from the east side of the lawn on Parliament Hill to the air base in nearby Rockcliffe.

Other officials were to have been transported by bus out of the city.