Halifax was and is a major Maritime port. During World War I the port served as a staging area for supply convoys heading from North America to England.
On December 6th, 1917 the Belgian relief vessel Imo, a converted whaling vessel, left the harbour and headed out to sea. On its way into port was the French tub Mont Blanc, a vessel so painfully slow that it was unable to keep pace with the faster American convoys and had been sent to Canada to join a slower group of vessels.
Mont Blanc was an ammunitions vessel, containing 300 rounds of ammunition, 10 tons of gun cotton, 2,300 tons of picric acid, and 400,000 pounds of TNT. Stacked on deck were a further 35 tons of fuel drums. Unfortunately, Mont Blanc was not flying the red flag that would have indicated to observers that she was an ammunition vessel.
As Imo approached the Mont Blanc, crew of both vessels found that they were in the same channel. An exchange of signals failed to resolve the dispute, and at the last moment Mont Blanc tried to cut across Imo's bow so the ships could pass starboard to starboard. However, both crews had gone full speed astern and the collision was inevitable.
Imo's bow struck the Mont Blanc amidships, shooting sparks into the picric acid and igniting the fuel drums on deck. Mont Blanc's crew immediately abandoned ship and rowed for shore as the Mont Blanc drifted towards the Halifax docks. As she burned, she was boarded by a firefighting party from a British warship in the harbor and tug boats were dispatched to attempt to get her out of the channel. The temperatures in the hold were climbing alarmingly, and the paint on the hull began to blister from the intense heat.
Mont Blanc drifted up against the piers along the side of the channel. By this time many onlookers, including children, had gathered to watch the spectacle. Without the red flag of warning flying on Mont Blanc, few realized the danger.
The Halifax Fire Department arrived, unaware of Mont Blanc's cargo. They were hooking their fire engine up to the nearest fire hydrant when at 9:35 am the Mont Blanc detonated in a huge explosion which engulfed the harbour and half of the city itself. Many other ships were demolished or thrown completely clear of the harbour up onto the shoreline.
One recorded act of bravery was that of telegraph operator Vince Coleman. He saw what was happening and started to flee, but then ran back to his post to warn incoming trains of the danger. Vince was one of the more almost 2,000 casualties when Mont Blanc disintegrated.
This "rather large" explosion was the largest man-made explosion on record before the first nuclear bomb tests. The shank of the Mont Blanc's anchor flew 2.3 miles over the entire peninsula of Halifax to land on the mainland side. The rear deck cannon went 3 miles the other way. A cargo box propelled by the explosion landed in Dartmouth.
Compiled from a number of online and print sources including http://www.region.halifax.ns.ca/community/explode.html