The Halifax Explosion is a rather large detonation that took place in the middle of the Halifax Harbour, a harbour in Halifax, Nova Scotia, Canada. It happened in the middle of World War I, and was caused by the impact between two ships, one loaded for bear with munitions, the other who-knows-what (something non-volatile). The collision took place as a result of a communications error; ships are supposed to signal with a series of horn blasts advance, port turn, starboard turn, and reverse; an erroneous blast caused the ships' ideas of each others' purposes to be misconstrued, and they collided.

The Halifax Explosion virtually annihilated half of both Halifax and Dartmouth, its twin city. The explosion has worked its way very deeply into the history and psychology of Maritimers (people who live in the Maritime provinces).