HALIFAX -- A boy presses his small face up to a cold window pane. It's an early winter morning, and two ships in Halifax harbour are exchanging a cacophony of horn blasts.

Vessels use these loud whistles as they pass, the boy's mom explains.

But today, Dec. 6, 1917, they do not pass.

The Norwegian relief vessel, the SS Imo, collides with a French munitions ship laden with explosives, the SS Mont Blanc. For 19-1/2 minutes, a dazzling display of fireworks captivates onlookers as the Mont Blanc drifts and burns.

The toddler, playing with a toy train on the kitchen window sill, watches the flames engulf the ship -- the last images he will ever see.

At 9:04 a.m., the Mont Blanc blows up with devastating force, its 2,600 tons of explosives levelling swaths of Halifax and Dartmouth, raining down shards of white-hot iron, blowing off roofs and shattering glass -- including the windows of a small wooden house in the city's north-end Richmond neighbourhood.

There, at age two years and seven months, Eric Davidson is blinded in the Halifax Explosion.

"My father was still looking out and all the glass came in on his face and his upper body," his daughter, Marilyn Elliott, said in an interview.

"Doctors looked at him and determined that his eyes couldn't be saved. Both of his eyes were removed that day. In an instant, a little baby, a happy-go-lucky baby, is without sight."

As a little girl, Elliott grew up knowing her father was blinded in the horrific blast that claimed nearly 2,000 lives, injured 9,000 and left 25,000 homeless. But it wasn't a topic that was openly discussed in her family.

The wartime disaster was mentioned in passing, in hushed tones, with a heavy heart.

"My grandmother was a changed woman after the explosion. She grieved the loss of her baby boy's eyesight," Elliott said. "It was a permanent trauma that she carried with her the rest of her life."

A hundred years after the greatest human-made blast before the atomic bomb, the country is commemorating the explosion's centennial with a large memorial service at Fort Needham Memorial Park. Dozens of organizations have received grants for museum and art exhibitions, theatre productions, documentary films and concerts. Canada Post has issued a striking commemorative stamp, a new plaque has been erected, a time capsule created and books published.

But the Halifax Explosion anniversary wasn't always so publicly remembered.

For many years, Dec. 6 passed quietly in this East Coast town, with a small service or private prayers, but no official public ceremony marking one of Canada's worst humanitarian disasters.

In the wake of a deafening blow and billowing white smoke that rose thousands of metres above the harbour, a silence settled over the city: It would take decades before the blackout was lifted, and the heartwrenching stories of the Halifax Explosion told.

"People tried to forget it. You don't carry that stuff around."

Jim Cuvelier, a 101-year-old survivor of the Halifax Explosion, said the disaster wasn't spoken of when he was growing up.

"People tried to forget it. You don't carry that stuff around," said Cuvelier, a baby who was at home on Lady Hammond Road on the outskirts of the blast zone at the time of the disaster. "I never heard them talk about it."

Mothers couldn't bear the deaths of innocent babies. Children disappeared without a trace. Others turned up days later in makeshift morgues. Girls and boys struggled to comprehend being suddenly orphaned. Wives mourned their husbands, killed instantly in harbourfront factories. Soldiers grappled with the insurmountable trauma of watching homes burn to the ground, families still inside, the scent of burning flesh in the air.

"The city was devastated. It was such a cataclysmic event, so traumatic, that I think people probably didn't want to revisit those horrors," said Craig Walkington, chairman of the Halifax Explosion 100th Anniversary Advisory Committee. "It really did do incredible damage. There was virtually no family that wasn't touched by it, whether injuries, fatalities, or a loss in some way."

The horrors witnessed by survivors on that day 100 years ago were, for many decades, unspeakable. The blast wiped out much of Halifax's densely populated north end and parts of Dartmouth, including a Mi'kmaq settlement known as Turtle Grove, and badly damaged the African-Nova Scotian community of Africville.

The shock wave of the explosion was felt as far away as Cape Breton, and windows nearly 100 kilometres away cracked. It was followed by a towering 15-metre tsunami, drowning survivors near the shore and sweeping many bodies out to sea. Upturned cook stoves ignited fires that consumed wooden homes, scorched entire blocks and made the rescue of some injured survivors trapped inside homes impossible.

That night, a blizzard blanketed the city with more than 40 centimetres of snow. "It got cold and the snow buried bodies. The next three days were a horror story," local author and historian Dan Soucoup said. "They found children two or three days later huddled and frozen in the snow."

Relief efforts were badly hampered by the cold and snow. Still, miraculous stories emerged from the rubble.

A soldier walking through the flattened Richmond neighbourhood a day after the explosion heard a faint whimper coming from a burned-out house. He walked through the charred debris and there, protected under an ashpan, he found a baby girl. The 23-month-old orphan, nicknamed 'Ashpan' Annie, was burned but alive.

In some cases, entire families were killed. In others, one survivor lived on. One woman, Mary Jean Hinch, lost 10 children and her husband in the explosion. Pregnant and alone, she was rescued after being pinned under lumber for 24 hours. She and her unborn son were the only survivors in her family.

Other harrowing tales from the front lines speak of near mythical courage. A train dispatcher, Vince Coleman, spent his final minutes warning an incoming train of the impending blast, prompting it to halt in its tracks and saving passengers and crew. In another case, most of the crew aboard the Stella Maris died attempting to attach a line to the Mont Blanc to tow it away from bustling Pier 6.

"He worked for 40 hours removing eyes."

The disaster, towards the end of the First World War, made headlines around the world.

"I have newspapers from all over the world. The Halifax Explosion shared the headlines with the major war-time events. It was not just some local thing," said Janet Kitz, author of several books on the Halifax Explosion.

As stories of the disaster got out, generosity flooded in. Children in Brantford, Ont., gave up their Christmas presents to raise money for the children of Halifax, donating $15,000 for relief efforts. People in Truro, N.S., lined the tracks at the rail station waiting to help the waves of refugees that arrived from Halifax in need of food and shelter.

The city's hospitals were inundated with wounded survivors and several emergency medical stations were set up in schools and clubs. Although aid arrived from across Canada and the United States -- particularly Boston, a city Nova Scotia still thanks every year with a Christmas tree -- many of the first medical responders on the scene hailed from nearby communities. Doctors, nurses and firefighters from across the Maritimes showed up to take on the harrowing task of aiding the injured.

George H. Cox, a doctor and eye specialist from New Glasgow, about 150 kilometres northeast of Halifax, arrived at the Rockingham train station outside Halifax the next day. With the tracks into the city destroyed, he trudged through deep snow to Camp Hill Hospital. Men, women and children lined the corridors, many with glass, pottery, brick, mortar and nails stuck in their eyes. He quickly realized that the large number of ocular injuries required his expertise.

"He worked for 40 hours removing eyes. He had a bucketful of eyes," Soucoup said. "He chased everybody out, slept for three hours, and did that again."

Halifax's mortuaries were also overwhelmed. Bodies, charred and frozen, were stacked like firewood outside funeral homes. Many unidentified corpses were stored in a school basement. Funerals went on for weeks, and services for the unidentified bodies drew thousands of mourners.

"Everything that could go wrong did go wrong."

As the body count climbed, bereaved locals, politicians and newspaper editors began questioning the cause of the blast and demanding to know who was responsible for the calamity. Details of the collision emerged during a judicial inquiry and legal proceedings, though few got the answers they were seeking.

When the Mont Blanc, laden with thousands of tons of explosives, came upon the Imo on the wrong side of the harbour, it asserted its right-of-way using loud whistles -- the very horn blasts that attracted little Eric Davidson.

"The Mont Blanc did have the right to the channel. But the Imo was stuck on a course it couldn't get out of," said Joel Zemel, an author and historian. "By the time they realized it, it was too late to avoid an accident. Everything that could go wrong did go wrong."

The initial investigation pinned the blame on three men: The Mont Blanc's captain, its pilot and the Royal Canadian Navy's chief examining officer in charge of the harbour. Given the Mont Blanc's explosive cargo, it was said that the burden rested with its crew to avoid a collision at all costs.

In the end, however, the Supreme Court of Canada and the Judicial Committee of the Privy Council in London found both the Mont Blanc and Imo were equally to blame for the navigational errors that led to the crash. No one was ever convicted in the disaster.

Yet questions persisted, like why the crew of the Mont Blanc didn't scuttle the ship, or steer it out to sea. "They were criticized heavily for being cowards," Zemel said. "But it would have taken six hours to sink the boat. And they thought they only had 10 seconds, not 19-and-a-half minutes."

The ship's cargo included wet and dry picric acid, TNT, gun cotton, benzol and other ammunition. "They were just a floating bomb. They could have tried to warn people but they didn't want to die. It was run for your life," he said.

"The city went to sleep until the Second World War."

Despite the enormity of the catastrophe, Halifax was forced to slowly pick up the pieces and move on. Swaths of the city had been levelled, and rebuilding was necessary to assuage the misery and anguish of survivors. Tents on the Commons had given way to rows of wood and tarpaper tenements near the current site of the Halifax Forum, but more permanent homes were desperately needed.

Prime Minister Sir Robert Borden promised the full resources of the federal government would be placed at the city's disposal, said Barry Cahill, author, researcher and member of the Halifax Explosion advisory committee.

Nearly $30 million was set aside for the Halifax Relief Commission to assist with medical care, rebuild infrastructure and establish pensions for injured survivors. One of the commission's lasting legacies is Canada's first public-housing project, the Hydrostone development not far from the blast site itself. "They had the good sense to retain a famous English town planner, Thomas Adams," Cahill said. The English-style garden suburb was completed in 1920.

As homes, churches, schools and factories were rebuilt, Halifax residents pushed the terror of the explosion from their minds, in part out of necessity. With hard times ahead, people struggled to get on with their lives.

"It wasn't an easy time in the 20s and 30s. There was a lot of depression here. Economically it was a difficult time in the Maritimes," Soucoup said. "The city went to sleep until the Second World War."

Halifax survivors were also fatigued by the news of endless First World War casualties in Europe.

"People were a wee bit hardened because of war," Kitz said. "The Nova Scotia Highland Regiment was at Passchendaele and several hundred men had been killed and wounded. Each day brought newspaper lists of those killed in action and hospital ships carrying wounded men arrived regularly."

"Somehow you were expected to just get on with it."

It took generations for the disaster to be commemorated. After the one-year anniversary, the city didn't hold another official public memorial until the 50th anniversary in 1967. Church services were observed and small ceremonies organized, but Halifax's collective psyche was not yet ready to publicly recall the calamitous blast that claimed so many lives.

"It could have been too painful in the early days," Elliott said, noting that even after the service in 1967 it once again fell by the wayside. "Why was it forgotten? No one has the answer to that. It could have been a sign of the times. Back then, people didn't like to dwell on misfortune. It wasn't really talked about."

Kitz wonders if the commemoration of the Halifax Explosion would have been different had it happened in another part of the city.

"It happened in the north end of the city, where it was mainly working-class people. If City Hall had been destroyed or the big businesses of the south end had been decimated, it would have been slightly different maybe. It's hard to say. Somehow you were expected to just get on with it. And that's what people did."

It was Kitz's tenacious research that helped change that.

In 1980, she penned an original undergraduate essay on the Halifax Explosion that led her to uncover boxes of mortuary artifacts gathering dust in the dark basement of Province House. She carefully catalogued objects that belonged to the dead, such as a child's Richmond School notebook with the words "Thou Eternity Away Forever" scrawled at the bottom of a page. "I quickly found it wasn't the objects in themselves that were intrinsically interesting. It was the people behind the objects," Kitz said.

She interviewed survivors who had been children in 1917, many of whom had never spoken of the enormous explosion out of respect for the impenetrable grief of their parents.

"Their mothers would never speak of it, because many of the fathers and children had been killed," Kitz said. "For a mother who lost perhaps a husband and two children ... it must have been just appallingly difficult. I don't think the mothers could ever have spoken openly of what they went through."

But older children who had survived the explosion opened up to Kitz about what transpired on that winter day so long ago. "They were eager to share their stories. Many of the younger survivors had very vivid, personal stories," Kitz said. "It wasn't so absolutely desperate for the children. There was almost a pride about being a survivor."

Kitz helped fundraise for a monument to victims of the disaster. In 1985, the Halifax Explosion Memorial Bell Tower was opened at Fort Needham Memorial Park overlooking the explosion site. Survivors and those wishing to pay their respects now had a place to assemble.

Kitz also helped mount an exhibit on the disaster at the Maritime Museum of the Atlantic in 1987, and two years later her best-selling book Shattered City further revived interest in the explosion.

Elliott, whose father passed away in 2009, offered another theory as to why the city nearly forgot about a seminal event that shaped its history: Survivors simply weren't ready to confront their memories.

"Those impacted the most by the explosion needed time."