Emergency Government Headquarters is the name given for a system of nuclear fallout shelters built by the Government of Canada in the 1950s and 1960s as part of continuity of government planning at the height of the Cold War. Situated at strategic locations across the country, the largest of these shelters are popularly referred to as "Diefenbunkers", a nickname coined by federal opposition politicians during the early 1960s. The nickname was derived from the last name of the Prime Minister of the day, John Diefenbaker, who authorized their construction. Over fifty facilities were built along several designs for various classes of service.