Nuclear warfare is unlikely even in the event of a third world war, as weapons of this kind are considered a last resort in most cases.
The only times they have ever been used is during World War Two, when the US dropped bombs on Nagasaki and Hiroshima to end the conflict in the Pacific theatre.
Since then, several other countries have developed their own nuclear programmes, and governments have drafted plans for what to do in the event of an attack on home soil.
The US Government has its own website dedicated to preparedness, ready.gov, which outlines what to do in the event of a nuclear attack.
source: express.co.uk