An explosion occurred in the harbor of Halifax, Nova Scotia on 6 December 1917, killing more than 2000 persons and injuring another 10,000. The explosion leveled a large part of the city and left at least 20,000 people homeless. It was the largest man-made explosion in history to that date, not surpassed until an atomic bomb was dropped on Hiroshima 3 decades later. The cause of the explosion was the collision of a Belgian ship, the Imo, carrying relief supplies to Belgium, and a French ship, the Mont Blanc, carrying 2600 tons of high explosives bound for France.
The harbor at Nova Scotia comprises an inner basin able to accommodate more than 100 ships, and invisible from the open ocean (and from enemy submarines). The narrow entry passage is flanked by industrial and cargo handling facilities. In the First World War (as well as the Second), Halifax Harbor was a major venue for assembling convoys from America to Europe.
On the morning of the collision, the Imo was steaming out of the inner basin as the Mont Blanc was bound inward. The Imo was off-course, forcing the Mont Blanc toward shallow waters at the edge of the narrows. Caught between imminent collision with the Imo and running aground, the Mont Blanc tried to escape by crossing the bow of the Imo. The maneuver failed and the collision set the Mont Blanc on fire. The ship drifted across the narrows toward the center of the city. Twenty minutes later, the Mont Blanc exploded.
The blast was powerful enough to transport a 1000-pound section of the Mont Blanc's anchor 2 miles away. Within and around the epicenter, the death rate was estimated to be 29 per 1000. Sixty percent of the deaths were male and 40% were female. Forty percent of deaths were under 20 years of age, 50% between 20 and 60, and 10% over 60. Data regarding injuries are limited; an estimated 20% of those permanently disabled were blinded by broken glass—they apparently had been behind windows watching the Mont Blanc in flames, when it exploded.