December 6 is Halifax's "day that lives in infamy". On Dec 6, 1917, two ships collided in Halifax harbour, the Imo and the Mont Blanc. The Imo was carrying relief supplies for WWI and the Mont Blanc was carrying explosives for the war effort. The Imo was leaving port as the Mont Blanc was arriving, both sailing in the same channel, one being the wrong one but neither ship seemed intent on changing it's course. At the last minute, the Mont Blanc pulled over into another shipping lane and the Imo went into a reverse to stop it's progress and by doing that, its course shifted the ship into the same lane the other ship had pulled into. They were still on a collision course and the Imo struck the Mont Blanc side on.
The sparks set the barrels of flammable explosive on the deck of Mont Blanc on fire. The crew abandoned ship but because they were French, most people on shore did not understand their warnings. Fire crews attempted to put out the fire on the ship as it drifted towards the Halifax shore but at 9:05 a.m. it exploded sky high. It was and is still the biggest man made accidental explosion ever and the largest before the nuclear age, and leveled the north end of Halifax and Dartmouth on either side of the harbour.
Hundreds of people had been on the shore watching the fire. As the warnings finally spread, one heroic railway worker warned a train that was approaching Halifax and would have progressed along the rails along the waterfront at the spot where the ship was on fire. Vince Coleman managed to warn the train in time so it was able to stop, but he died in the explosion minutes later. Two thousand were killed and thousands more were injured, many blinded from flying glass. A tsunami rose in the harbour from the force of the blast and washed many of the onlookers into the harbour. The Imo was lifted by the water onto the Dartmouth shore and most of the crew on board were drowned by the wave.
The anchor of the Mont Blanc landed 3 miles away by the Northwest arm and a gun barrel was found 2 miles away from the harbour in Dartmouth (just around the corner from where I live. It's now mounted with a memorial plaque)
Thousands were homeless and windows broke all over the city. China rattled on shelves as far away as Truro and New Glasgow, some 75 miles away. The next day, a winter blizzard blew in.
The army set up rows of tents for temporary shelter. Schools and churches were turned into hospitals and mortuaries all over the city.
The city of Boston immediately sent a train full of supplies and medical help, the first among many other places to offer help. Every year for the last 35 or so years, Nova Scotia donates a Christmas Tree for Boston's city square in thanks.
The city slowly crawled to its feet, rebuilding began in the spring. There is a memorial on Fort Needham in the north end and a service there every year on the anniversary. There are still a few people who survived the explosion alive, in their 80's and 90's but slowly the last survivors are passing away. There are a lot of artifacts and photos from the Explosion at the Maritime Museum of the Atlantic on the waterfront.