During the period 1948 to 1963 civil defence in Canada developed in a number of stages that reflected changes in technology, weaponry and scientific discovery. The first stage of development, roughly between 1948 and 1952, witnessed only minor developments. Civil defence followed the Second World War practice, with a focus on air raid shelters and, if possible, evacuation. In the years 1952 to 1954 as the possibility of a nuclear attack became more real as a result of the Soviet development of intercontinental bombers, civil defence officials moved towards a policy of mass evacuation of target areas and the rescue of survivors. The detonation of a hydrogen bomb and the discovery of radioactive fallout in 1954 led to yet another change in civil defence plans. Civil defence officials became more convinced that mass evacuation of target areas was the answer, however, fallout shelters were also recommended for those areas outside the target area likely to be blanketed with radioactive debris. In the late 1950s and into the early 1960s civil defence again had to be redefined as intercontinental ballistic missiles (ICBMs) were developed and evacuation was no longer possible as nuclear attack could occur virtually without warning.
Davidson, Mark "Preparing for the Bomb: The Development of Civil Defence Policy in Canada, 1948–1963." Canadian Military History 16, 3 (2007)