A 1961 nuclear attack drill goes awry. 

Air raid sirens rang out from coast to coast, and an eerie voice announced that Canada was under attack: 14 nuclear missiles were inbound. The sombre voice then went on to tell startled citizens that this was the beginning of a country-wide drill, and that for the next 24 hours Canada would be behaving as if it had just been the subject of a massive nuclear strike. 

https://backyardhistory.ca/articles/f/dont-forget-to-tell-the-public-about-the-mock-nuclear-attack