The largest bang before the bomb

A munitions ship burning in Halifax harbour blew up at four minutes past nine, killed about 1,800 people, and flattened a square mile of the city.

A railway dispatcher, Vincent Coleman, stayed at his key to stop an incoming passenger train and was killed sending the message. It was the biggest artificial explosion in history until 1945, and the blast wave is still used as the yardstick for what a few kilotonnes of chemical explosive does to a town.