“The explosion turned two square miles of this calm, postcard-pretty town into a nightmare of chaos, destruction, and death in a split second.”

AT EXACTLY 9:04 A.M. on the morning of Dec. 6, 1917, the bustling wartime port city of Halifax, Canada was rocked by one of the largest non-nuclear explosions in history.

The blast occurred just minutes after the French freighter SS Mont-Blanc, which was loaded with 3,000 tons of high-explosives bound for the war in Europe, caught fire following a collision with the Norwegian vessel Imo in the town’s busy harbour.

In moments, the Mont-Blanc’s volatile cargo detonated. The force of the blast was equal to a 2.9-kiloton nuclear warhead. In a split second, Halifax vanished into a fireball that levelled much of the city. Every building within a half-mile of ground zero was flattened; hundreds of structures beyond the blast radius were severely damaged. More than 2,000 inhabitants of Halifax and the nearby town of Dartmouth perished in the conflagration, another 9,000 survived, but were horribly burned, struck by flying debris or crushed beneath the rubble.

Aid for the survivors poured in from across North America, but it took years for the city to fully recover. While the entire episode today remains a footnote to the wider tragedy that was the First World War, the people of Halifax still remember the events of Dec. 6, 1917.

This year, Canada marks the 100th anniversary of the catastrophe. To help commemorate this grim wartime milestone, MilitaryHistoryNow.com interviewed John U. Bacon, journalist, historian and the bestselling author behind the book The Great Halifax Explosion: A World War One Story of Treachery, Tragedy and Extraordinary Heroism. Here’s what he told us.

MHN: What made you want to tell this story? Why do you think it’s worth telling?

I first heard about the Halifax Explosion from my Canadian grandfather, who was 12 years old in 1917 when Mont-Blanc blew up. He often told me stories about the disaster, but I never heard or read about it anywhere else.

For decades, his stories slept in my memory until I began writing my first book — it was about the history of the University of Michigan’s hockey program. During my research, I learned the program’s founder, Joseph Barss, had been a first responder of the Halifax explosion. When I read about it, I learned my grandfather hadn’t exaggerated the calamity. The story captured my imagination for years, and now I finally have the chance to tell it.

MHN: Mont-Blanc sailed from Brooklyn with 3,000 tons of explosives aboard. Was anyone concerned about the risks?

By mid-1917, the fourth year of World War One, risks that would be unacceptable in pursuit of commerce suddenly became tolerable when placed against daily casualty lists, which could run into five figures on a given day. In Gravesend Bay, New York, dockworkers loaded Mont-Blanc with one of the largest caches of high explosives ever packed on a ship: 62 tons of gun cotton, similar to dynamite; 246 tons of an airplane fuel called benzol; 250 tons of TNT; and 2,366 tons of picric acid, which is more powerful than its cousin, TNT. The total weight of almost six million pounds was about 13 times the weight of the Statue of Liberty, packing one fifth the power of the first atomic bomb unleashed on Hiroshima.

A second problem was Halifax Harbour. Shipping traffic had expanded exponentially during the war, but the captains and harbor pilots had grown lax about nautical conventions. The port’s own chief examining officer (CXO), F. Evan Wyatt, warned his superiors about the danger. “It is not possible to regulate the traffic in the harbor,” he wrote. “And it is submitted that I cannot in this regard accept the responsibility for any accident occurring.” Wyatt’s warnings went unheeded.

MHN: How could a disaster like this have been prevented?

Like so many man-made disasters, this one could have been nipped in the bud a dozen different ways, including these four:

First, the ship was dangerously loaded. After the stevedores in New York had carefully stowed the cargo, they received a final order to add the 494 barrels of benzol, which they stacked three and four barrels high and lashed with ordinary canvas straps — a slapdash approach. Because the airplane fuel needed only a spark to ignite, they had unwittingly constructed the perfect bomb, with the easy-to-light fuse on top, and the most powerful materials trapped in the hold below.

Poor equipment was another factor. The ship’s forward deck had a connection for a pressure hose that could draw water from the sea in case of a fire, along with two anchors that could be dropped from the bow to secure her in an emergency. But when the blaze started on the bow, both were were rendered useless.

Even after the Norwegian  vessel had ripped a hole in the side of Mont-Blanc, a quick thinking bridge crew could have prevented the blast. As the flames reached the benzol on deck, harbor pilot Francis Mackey urged Captain Le Medec to point the ship out to sea and steam away from Halifax. The speed might have forced enough seawater into the gash in the hull to douse the fire and swamp the explosives. Instead, Captain Le Médec shouted, “Abandon ship!”

Finally, the crew failed to alert residents on the shore of the danger they were facing. Instead of pulling for Halifax where thousands had gathered to watch the burning ghost ship, the crew rowed across the harbor toward Dartmouth, which was much farther. They warned nobody en route. If they had, word might have gotten to the central command, which could have saved countless lives.

MHN: Describe the force of the blast? How widespread was the destruction? 

In one-fifteenth of a second, five times faster than the blink of an eye, the epicenter of the explosion instantaneously shot up to 9,000 degrees Fahrenheit, about six times hotter than molten lava. The blast shot outward in all directions at 3,400 miles per hour, or four times the speed of sound. It tore through the ship’s steel hull like wet tissue paper, converting the vessel into a monstrous hand grenade. The heat vaporized the water surrounding the ship and the people trying to put out the fire. The remains of these victims were never found — there were no remains to find.

Mont-Blanc left only two recognizable parts: the anchor shank, which weighed half a ton and was found four miles away in the woods of the Northwest Arm of the harbour; and an iron deck cannon, which landed three miles away with its barrel drooping like a warm candle.

All told, the explosion turned two square miles of this calm, postcard-pretty town into a nightmare of chaos, destruction, and death in a split second.

A Canadian television “Heritage Minute” commemorates an unlikely hero of the Halifax explosion.

MHN: Who were some of the unlikely heroes that emerged from the story? 

One was train dispatcher Vincent Coleman. When he learned the burning ship’s cargo was high explosives, he ordered his staff to run and led the way until he remembered a train was due to arrive with 300 passengers. He stopped, ran back, and rattled off an urgent telegraph to stop the train.

“Hold up the train. Ammunition ship afire in harbour making for Pier 6 and will explode. Guess this will be my last message. Good-bye, boys.”

Coleman’s telegram was received right before the explosion knocked out the lines. As a result, other cities soon learned of the disaster and sent help.

Then there were the countless Americans who leapt into action. An hour after hearing about the blast, Boston’s leaders ordered two trains and two ships to be loaded with food, clothing, bedding, motor trucks and medical supplies. Also aboard were welfare workers, 100 doctors, and 300 nurses – all volunteered without being asked. This generosity helped transform 141 years of distrust, subterfuge and occasional violence between the two nations into a friendship that has stood for a century. The relationship stands as an example to the rest of the world.

The Canadian military did their bit too. Soldiers stationed nearby did almost everything that needed to be done, from rescuing victims from burning buildings to transporting them to makeshift hospitals to securing what remained of Halifax – all without complaint.

Finally, there was the sacrifice and compassion of ordinary citizens. Years later, the survivors seemed to remember those tender mercies as clearly as the horrific scenes, perhaps because they provided tangible proof that human kindness had not been erased even by the greatest man-made explosion the world had ever seen.

MHN: What was the fallout from the explosion? Was anyone held responsible? Were there any lessons learned from it?

The Canadian and British legal systems pursued this question during four judicial tribunals. The captain of the Norwegian vessel Imo had committed violated far more basic nautical conventions than did Mont-Blanc’s skipper, but only the men on the French freighter knew they were sitting on six million pounds of explosives. Imo’s crew paid with their lives, while Mont-Blanc’s ran for theirs—without giving a thought to mitigating the pain suffered by so many, or even expressing sympathy afterward. While those omissions don’t constitute crimes, they certainly coloured how the people of Halifax regarded them.

In the cosmic scheme of things, splitting the legal blame might be as close as anyone could get to justice. By the time the final decision came down, locals had already moved on to rebuilding their lives and their city.

Halifax learned to take its safety procedures seriously. City leaders replaced patronage in civil service jobs with a meritocracy, which helped prevent any similar disasters during World War Two.

MHN: How is the explosion remembered in Canada? 

Halifax native Robert MacNeil, creator of PBS’ MacNeil-Lehrer Report fame, has said Canada suffers from a national amnesia about the Halifax disaster, with few under 50 years-old knowing anything about it.

And yet, every winter the people of Nova Scotia spend $180,000 to send the province’s best Christmas tree to Boston Common, as a thank you for that city’s tremendous help a century ago, a testament to a time when the worst the world could inflict brought out the best in two countries. The hard-earned friendship those days forged has stood as an example to the world for a century.

“Why,” one Nova Scotian asked, “do we have to stop saying ‘Thank you!’?”

MHN: What can Halifax teach us?

Danger in various forms has always been with us, and always will be. For the vast majority of us, who stare out our windows as we sip our coffee in the morning, the bigger lesson of Halifax is how to respond if the worst occurs.

The explosion should have shredded the social fabric that kept a civil society like Halifax’s intact. If you wanted to walk into someone’s house or business and take things, there wasn’t much stopping you. But with society’s infrastructure decimated, something more noble rose up to replace it: the primal instinct to take care of one another, especially the old and the young, and give them shelter, food, help, and kindness—from sending ships and trains from Boston to insisting that needier patients go first to cleaning the scalps of two kids during a haircut for free—all with no thought of being paid back.

When the laws no longer applied, basic human decency proved even stronger. After the Halifax explosion, the survivors demonstrated the incredible human capacity for courage and compassion, reservoirs that we might be able to call upon to save a stranger’s life at a moment’s notice. If that day ever comes, we can only hope to respond as well as the good people of Halifax and Boston did.

John U. Bacon is the author of five New York Times bestsellers, including Three and Out; Fourth and Long; and Endzone. His latest book is The Great Halifax Explosion. Bacon appears often on NPR and national television, and teaches at Northwestern University’s Medill School of Journalism and the University of Michigan. He lives in Ann Arbor with his wife and son.