History rerun: December 6, 1917

It was World War I.

Gigantic convoys of ships carrying weapons, food, and troops went constantly to Europe, bringing supplies to the Allies. They left from several major Canadian and American ports.

On this day one of them went horribly wrong. And outside of where it happened, it's mostly forgotten.

A large convoy was gathering in Halifax harbor for the trans-Atlantic journey. One ship was a freighter heavily loaded with explosives, the S.S. Mont-Blanc.

At 8:40 that morning, due to a series of mutual errors, she collided with the freighter S.S. Imo.

The Mont-Blanc immediately caught fire. Her crew tried to put it out, but due to its rapid spread were unable to. Scuttling attempts were unsuccessful, and the crew were forced to abandon ship. Someone rang a fire alarm, and several firefighting teams quickly responded to the docks. But with the ship in the harbor, there was little they could to but watch it burn. None of them knew about its cargo.

At 9:04 a.m. the disaster happened.

The ammunition cargo on the Mont-Blanc exploded with the force of 3 kilotons of TNT (roughly 1/5 the strength of the Hiroshima atomic bomb). To this day it remains the largest accidental explosion in human history, and until the 1945 nuclear tests was the biggest man-made explosion ever. Windows were shattered 10 miles away. Objects fell from shelves 80 miles away. The explosion was heard over 200 miles away.

A mushroom cloud and fireball rose over a mile into the air, and a tsunami wave of water, 60 feet high, was sent surging into Halifax. The steamship Imo was picked up and thrown ashore like a toy. Many people (including the firemen) who'd gathered ashore to watch, or were trying to get to the Mont-Blanc to help, simply vanished.

Fire spread through the city. Since it was winter, many homes had furnaces and heating stoves alight, and the shock wave blew them over, spreading heating oil and coal on the ground. Red hot shards of the ship's metal rained everywhere in the city, starting fires in buildings not directly affected by the explosion. A half-ton section of the Mont-Blanc's anchor was thrown over 2 miles into the city, and is now part of a monument. To this day St. Paul's Church has a piece of wreckage embedded in the building.

The city within 1 mile of the entire explosion (326 acres) was utterly destroyed. Buildings, docks, warehouses, homes, and people- all gone in a few seconds. Large fires swept quickly through many city blocks, fueled by winter stores of coal and heating oil. An inferno grew quickly.

Many of Halifax's rescue workers were injured or killed by the explosion, and so the city's ability to react was already impaired. Firefighters from nearby communities came to help- only to find that fire hose and nozzle sizes weren't standardized, and they couldn't connect to the Halifax hydrants. In spite of this, they and surviving local crews worked valiantly to put out the fires, and began rescue efforts of the many trapped under collapsed buildings.

But it was a northern Winter, and darkness came early, along with bitter cold. Rescue workers struggled through the night, chasing voices and moving frozen debris by hand.

The dawn brought light- and a heavy snowstorm. It became the largest blizzard of that decade, dropping 16 inches of snow in a few hours. It put out the last of the fires, but also impaired efforts to reach those who were trapped. Many survivors stuck under debris died from exposure while awaiting rescue.

This view overlooking Halifax harbor was taken after the snowstorm. This had previously been a busy neighborhood and business district.

All told, roughly 2,000 people died- 600 of them under 15 years of age. Another 6,000 were seriously injured, with 9,000 total wounded. 31,000 more were either homeless or had only minimal shelter. Many of the wounded were blinded by flying glass, and care for them eventually led to new treatments for eye trauma.

Although there were many heroes that awful day, one man stands out. His name was Vince Coleman, and he was a railway dispatcher ashore. When he learned of the burning ammunition ship, he realized that a loaded passenger train would be at the waterfront depot in a few minutes. Instead of saving himself, he ran to the telegraph key and quickly tapped out "Stop trains. Munitions ship on fire. Approaching Pier 6. Goodbye." He was killed a few seconds later in the explosion, and is credited with saving at least 300 lives.

Local hospitals overflowed with the dying and wounded, and anyone with medical training was pressed into work. The overtaxed Canadians were assisted by medical crews from American and British warships that had gathered for the convoy. An old ocean liner was turned into a hospital ship overnight. Other medical responders arrived, sent from all over Nova Scotia to assist.

Word of the disaster reached America in a few hours, and the state of Massachusetts rapidly organized a relief effort. All available trains in Boston were frantically loaded with food, medical supplies, shelter materials, and volunteer rescuers and medical personnel. The first train left Boston the night of the explosion, chugging through the same blizzard that was impairing relief efforts, and arriving roughly 30 hours later. It was followed by many other trains from all over Eastern Canada and America. The supplies and workers they brought are credited with keeping the death toll from going higher.

It's been 95 years since the tragedy, and the American assistance hasn't been forgotten. To this day Nova Scotia annually chooses it's finest Christmas tree and sends it as a gift to the city of Boston. This is the tree that stands in Boston Common every holiday season, remembering assistance in a time of need.