On the morning of 6 December 1917 the French cargo ship SS Mont-Blanc collided with the Norwegian vessel SS Imo in the harbour of Halifax, Nova Scotia, Canada. The Mont-Blanc, laden with high explosives, caught fire and exploded, devastating the Richmond district of Halifax. At least 1,782 people were killed, largely in Halifax and Dartmouth, by the blast, debris, fires, or collapsed buildings, and an estimated 9,000 others were injured. The blast was the largest human-made explosion at the time. It released the equivalent energy of roughly 2.9 kilotons of TNT (12 TJ).

SS Mont-Blanc was a cargo steamship that was built in Middlesbrough, England in 1899 for a French shipping company. On Thursday morning, December 6, 1917, she entered Halifax Harbour in Nova Scotia, Canada laden with a full cargo of highly volatile explosives. As she made her way through the Narrows towards Bedford Basin, she was involved in a collision with Imo, a Norwegian ship. A fire aboard the ship ignited her cargo of wet and dry 2,300 tons of picric acid, 500 tons of TNT, and 10 tons of guncotton. The resultant Halifax Explosion killed approximately 2,000 people and injured about 9,000.