The largest non-nuclear man-made explosion occured in the maritime city of Halifax, Nova Scotia on December 6, 1917 when a troop ship collided with an ammunition ship bound for the battlefields of Europe in the city harbour.
Halifax is one of the world’s largest and deepest ice-free harbours, and during the war it became a major military installation. A large army garrison was stationed there, and a vast bureaucratic machine was set up in the city. All neutral ships bound for North America had to report to and be inspected in Halifax. As a result of these factors, the city experienced a massive growth of population and size, from 50,000 in 1914 to over 150,000 by 1917.
For 3 1/2 years the Dominion of Canada had been heavily involved in the First World War. In 1914, when Great Britain went to war, all her colonies and dominions had to do the same. During the First World War Canada rose as an industrial power in the world and supplied the British war effort with over half of her supplies, material and grain. The Canadian army, under the skilled leadership of General Arthur Currie, had gained a reputation as shock troops on the Western Front and after the stunning victory at Vimy Ridge on Easter 1917 Canadian indepedence after the war was guaranteed.
Between 1914 and 1917 Canada had also become a middle-power with her navy. As more and more supplied poured into Britain and France from their far-flung empires, Germany began to employ the feared U-boats in the mid-Atlantic. To counter the U-boat threat, ships sailed in convoys escorted by warships. By 1917 over 52% of these convoys were assembled and sailed out of Halifax until the American war machine geared up by the spring of 1918. As a result, hundreds of merchant marine ships and their escorts would be jammed into Halifax harbour when a convoy was preparing to sail or returning from Europe.
With so many vessels crammed into the harbour it was inevitable that accidents would occur. Indeed, there had been several over the years and at least two ships had sunk, one a light destroyer when it ran aground during fog, and another a coal ship which collided with a freighter in the harbour.
In 1916 an American naval observer had written a report to the Naval Department in Washington, noting that “..with the current conditions in the city and the strains on the local administration, it is only a matter of time before we are witness to a significant maritime disaster.” The demands of the war, which by late 1917 had consumed millions of men in endless trench warfare in the bloodiest attrition the world had ever seen, meant that British and Canadian authorities were helpless to change the situation in Halifax harbour.
On December 6th, 1917, the fears of many experts came true. A convoy was assembling in the harbour and ships were lazily drifting about in the water as they waited. To reach the stormy Atlantic from Halifax Harbour ships must first pass through two natural channels called the Bedford Basin. Under normal conditions traffic is heavily controlled through these channels but on this day in 1917 the chaos in the harbour only guaranteed the disaster would happen.
The steamer Imo was heading through Bedford Basin when two tugboats pulling a coal freighter nearly collide with her. Imo took evasive action and veered hard to starboard. The steamer and the freighter just barely missed colliding. Unfortunately for Imo, she had veered directly into the path of the French ammunition ship Mont-Blanc. The Mont-Blanc blasted her whistles, to which the Imo replied, both ships signalling their intent to stay on course. Unfortunately it was a head-on collision course.
At the last minute both captain’s ordered full emergency full reverse, but the sudden change in pitch in the propellers caused both ships to slide quickly into the center of the channel, momentarily out of control. The Imo hit Mont-Blanc broadside at 15 knots and embedded into her starboard side. The Imo’s captain ordered rapid changes in propeller speed to try to dislodge the two ships, and this caused the intertwined metal to spark. Unfortunately for everyone, the Mont-Blanc’s hull had been breached during the collision and these sparks found the 6,000 tonnes of ammunition she was carrying.
A large fire immediately erupted all along Mont-Blanc’s hull, and her captain ordered everyone to abandon ship. Four minutes after the collision the Imo managed to tear herself free, her bow badly damaged but her hull intact. The Mont-Blanc was a sea of flame and sailors were throwing themselves into the cold water of the channel. A large store of benzol on the Mont-Blanc’s decks exploded in a huge fireball, but this was only a preview for what was to happen next.
The Mont-Blanc burned in Bedford Basin for nearly twelve minutes. The heat from the burning ship was so intense that it could be felt on the shore, and people came down to the docks to watch the drama unfold. At that time a train loaded with families bound for Halifax to wave goodbye to their sons as they set out for France was only thirty kilometers away. At the Halifax train station a young telegraphist, seeing the inferno on the water and perhaps sensing the imminent danger, fired off an emergency message to the fast approaching train. “Immediate Stop! Do Not Enter Halifax!” His last-minute message saved the lives hundreds of civilians.
At 9:04 am the Mont-Blanc suddenly exploded with a force of 3 kilotons, equivalent to 3 Hiroshima bombs. A massive fireball rose 2 km into the air, forming a giant mushroom cloud. The shock wave flattened buildings for 5 kilometers around the harbour and triggered a massive tsunami that rose 60 metres above the harbour and swallowed hundreds of houses and people. Shards of molten metal rained down on the city and 20 kilometres away.
The effects of the shock wave and tsunami were compounded by the narrow channels of Bedford Basin, which created a funnel-like effect. Unfortunately not a single person who was watching along the shores survived, so there were no eye-witnesses to the actual explosion to interview after the fact.
In Halifax’s north-end, the blast caused oil lamps and wood-burning stoves to tip over, and a conflagration consumed the city. Nearly 1200 houses were burned down in this secondary effect of the blast.
Researchers have since discovered that the effects of the blast were felt as far away as Cape Breton Island (360 km) and even in Vermont, where windows rattled and shelves collapsed in people’s homes (this was, at the time, attributed to a minor earthquake although scientists were stumped for many years about how, when none of the usual signs of an earthquake were present. It was in the 1960s that researchers discovered the tremors in Vermont were felt at 9:07 am, three minutes after the explosion, and the blast could be traced through Maine, New Brunswick, and Nova Scotia all the way to its epicenter in Halifax Harbour).
2,000 people lost their lives in the Halifax explosion, and 15,000 were injured. Over 12,000 homes, stores and buildings were destroyed by the shock wave and tsunami and countless others damaged. Fourteen ships of the assembling convoy were sunk in the harbour, more loss of material and ships than any German U-boat had managed to inflict on a convoy. The cost of the explosion, adjusted for today’s prices, is estimated at over half a billion dollars.
The Halifax explosion has become embedded in Canadian, and particular Nova Scotia, folklore and has since spawned numerous films, documentaries, songs, books and even poems. The Mont-Blanc’s 1.5 ton anchor, which was hurled 2 kilometers away, is now a memorial in Halifax, kept exactly where it fell from the sky and embedded in the earth.