Shortly after 8 a.m. on Dec. 6, 1917, the French munition ship Mont Blanc left Halifax's outer harbour en route to Bedford Basin.
To reach this safe inner harbour, the 320-foot Mont Blanc had to navigate through the Narrows, a 1.6-kilometre-long, 500-metre-wide passage separating the city of Halifax and the town of Dartmouth.
On Mont Blanc's bridge were 38-year-old Capt. Aime Le Medec and 45-year-old Pilot Francis Mackey, both of whom were aware of the ship's dangerous cargo: 2,300 tonnes of picric acid, 200 tonnes of TNT, 10 tonnes of gun cotton, and 35 tonnes of benzol.
Meanwhile, the 430-foot Norwegian-owned Imo, a ship commissioned to deliver relief supplies to Belgium, was steaming out of Bedford Basin and through the Narrows towards the harbour's mouth. To protect the ship from submarine attacks, Belgian Relief was painted in huge, red letters against a white background on either side. At the helm were Capt. Haakon From and Pilot William Hayes.
Due to miscommunications between the vessels, the Imo struck the Mont Blanc at approximately 8:30 a.m., slicing the ship's starboard bow and cutting a hole in her forward hold.
The vessels separated without much damage, but several of the Mont Blanc's drums of benzol were punctured and a raging fire erupted.
Pilot Mackey, Capt. Le Medec and all but one of the Mont Blanc's crew abandoned ship and rowed to safety towards the Dartmouth shore. Seeing the blazing vessel drift towards Halifax's Pier 6, the captain of the Imo steered for the harbour's mouth.
Crowds soon gathered near Pier 6 and sailors on nearby ships crowded the decks of their vessels to see the burning spectacle. Children on their way to school stopped on the slope overlooking the Narrows to view the excitement. Factory workers and stevedores stopped their work and scrambled for the best vantage points after hearing the city's new pumper fire truck Patricia racing to the pier.
Near the dockyard, both the depot ship HMCS Niobe and the light cruiser HMS Highflyer sent off boat parties to investigate the blazing munitions ship.
At 9:04:35 a.m., the Mont Blanc suddenly erupted in the largest human-made explosion prior to the detonation of the Second World War's atomic bombs.
The explosion ejected a deadly barrage of steel fragments, caused a tsunami in the harbour and created a pressure wave that levelled buildings, snapped trees and bent metal rails.
The blast was so powerful, one of the Mont Blanc's gun barrels was thrown almost five kilometres into Albro Lake on the Dartmouth side and part of her anchor sailed more than three kilometres into the woods of Halifax's North West Arm. The Imo, its superstructure obliterated, was hurled onto the Dartmouth shore by the tsunami. Soon, a towering pillar of greyish smoke with a mushroom-shaped cap rose over the harbour.
The blast, which rattled and broke windows 100 kilometres away in Truro, caused catastrophic destruction at ground zero. In just five square kilometres of Halifax and Dartmouth, 2,000 people died, perhaps 1,600 immediately. As many as 9,000 were injured, 6,000 seriously. More than 1,600 houses were destroyed and 12,000 damaged.
Following the disaster, a commission of inquiry placed complete responsibility for the collision on Capt. Le Medec and Pilot Mackey of the Mont Blanc. They were immediately arrested for manslaughter but the charges against both were later dropped due to insufficient evidence to prove criminal culpability.
Mackey was eventually allowed to return to work as a pilot; Le Medec continued his career without censure from the French government.
Meanwhile, the onerous, lengthy, and expensive task of relief and reconstruction for Halifax was carried on in large part due to the contributions of thousands of Canadians, including those from Manitoba.