The 1917 Halifax Explosion: The World’s Largest Accidental Man-made Explosion

By Donna K. Keesling

December 6, 1917 dawned bright and cold in Halifax Harbor in the Canadian province of Nova Scotia. A few hours later, more than a square mile of the waterfront had been levelled as a result of the collision of two ships and subsequent explosion of one of them.

Halifax Harbor, an inlet of the Atlantic Ocean, is one of the deepest ice-free ports in North America. A constricted passage, known as the Narrows, connects Halifax Harbor with Bedford Basin, a protected anchorage at its northwest end.

In December 1917, Halifax was fully engaged in the Great War in Europe – at least as much as any North American city could be. Along the Narrows, rail lines from the deep-water shipping terminals ran westward to the cities of central Canada and wheat farms in the prairies.[1] The rail lines and shipping facilities were integrated into the Canadian war effort. Because Halifax Harbor is the closest large port to Europe, it was where ship convoys carrying service personnel and supplies left to cross the Atlantic ocean.[2] It was also where ships brought injured soldiers to convalesce.

Early in the morning of December 6, the Mont-Blanc and Imo began their voyages – each heading in the opposite direction. The SS Mont-Blanc, a 320-foot French freighter, was carrying TNT, picric acid – also an explosive, barrels of the highly flammable fuel benzole, and guncotton, a propellant. In an article in The Washington Post, writer Steve Hendrix described the Mont-Blanc as a “floating, 3,000-ton bomb.”[3] It had been loaded in New York, but because of its lack of speed was not able to join a convoy in New York for safe passage across the Atlantic. It was sent to Halifax to join a convoy there. When the Mont-Blanc arrived on December 5, the anti-submarine underwater net was down at the port entrance, so it waited until the morning of December 6 to enter the harbor and head to Bedford Basin to rendezvous with other ships.

The SS Imo, a 430-foot Norwegian steamship under charter for the Belgian Relief Commission, had anchored in Bedford Basin while enroute to New York where it would load food and clothing for the people of Belgium.

According to Roger Marsters, Curator of Marine History at the Nova Scotia Museum, “a series of ill-fated moves ended with Imo striking Mont-Blanc’s bow” as they maneuvered for positions in the Narrows.[4] The out-bound Imo was reportedly traveling faster than what was considered safe. To avoid another ship and a tugboat, it entered the Narrows far to the left, heading into the path of the in-bound Mont-Blanc.[5] The ships then collided, bow to bow.

After the collision, a fire broke out on the deck of the Mont-Blanc. The crew, knowing how dangerous the cargo onboard was, quickly launched lifeboats and abandoned the ship. All of the Mont-Blanc crew survived except for one who was later hit by shrapnel.

The Mont-Blanc drifted towards the Halifax side of the harbor, coming to rest against Pier 6 in the Richmond District. After burning for about twenty minutes, the barrels on deck burst and triggered the blast. The iron hull was blown into shrapnel that rained down on the surrounding communities. The 1140-pound anchor shaft was projected for more than 2 ½ miles and landed on the Edmonds Grounds estate. The shaft was incorporated into a monument and still sits on the site.[6]

The Imo was beached on the Dartmouth shore following the explosion. The bridge crew, including the captain and the pilot, were killed.

Prior to the war, ships carrying munitions or explosives were required to anchor outside of the harbor and unload their cargo onto smaller ships which brought the cargo to shore. In addition, all ships carrying munitions were required to fly a red flag, and all surrounding ships were required to stop while it was moving. These rules were relaxed during the war so as to prevent German U-boats from identifying the ships with munitions and explosives.[7]

As the Mont-Blanc burned in the harbor, people ran to the docks and windows of nearby buildings. Without the red warning flags, they had no idea that it was a “floating bomb” about to explode. As a result of the explosion, nearly 1,800 people lost their lives and 9,000 people were injured. Many thousands of people were left homeless.

When the Mont-Blanc exploded, the Richmond district in the north end of Halifax and the Dartmouth region across the harbor were all but destroyed. The long-time settlement of the Mi’kmaq people, known as Turtle Grove, was leveled. Windows were shattered as far as 50 miles away. The sound of the explosion carried for hundreds of miles. A tsunami occurred in the inner harbor, resulting in “a surge of water sixty feet above the high-water mark, inundating buildings and facilities and scattering people and debris across several miles.”[8]

The first relief came from people in the surrounding districts. First responders also included soldiers and sailors from Canadian, British, and United States ships that were in port. A trainload of doctors, nurses, and medical supplies was dispatched from Massachusetts.[9]

The Halifax Relief Committee, a volunteer group, was organized within hours of the explosion. In addition to rescue and relief, the organization performed identification of the dead and injured, provided shelter for homeless, appraised damaged and demolished structures, and constructed temporary housing.[10]

On January 22, 1918, the Halifax Relief Commission was appointed by federal Order-in-Council to coordinate the reconstruction work and oversee the expenditure of close to $21,000,000 that had been donated by the public and the governments of Canada, Great Britain, and other countries.[11]

In 1918, Nova Scotia sent a Christmas tree to Boston, Massachusetts as a way of thanking Bostonians for their help following the explosion. The tradition was restarted in 1971 and continues unbroken to this day. Citizens of Nova Scotia nominate trees, with the winner selected by a committee. The tree is typically a 40 to 50 foot tall red or white spruce, or balsam fir. It is loaded onto a flatbed truck and travels to Boston to be set up on the Boston Common. On November 30, the mayor of Boston is joined by the Nova Scotia premier for a tree-lighting ceremony. The tree even has its own Facebook page – Tree for Boston!

You can learn more about the explosion by visiting the Maritime Museum of the Atlantic in Nova Scotia. In 1994, a permanent exhibit about the explosion entitled “Halifax Wrecked” was opened. The exhibit was updated and reopened as “Explosion in the Narrows” in 2019. Detailed information, including photographs, is also available on the Nova Scotia Archives page titled 1917 Halifax Explosion.

The explosion is still considered “the world’s largest accidental man-made explosion.”[12] The hands of the town hall clock tower, broken during the explosion, remain fixed at 9:05 – a lasting testament to the explosion and devastation that took place that day.


“A scene following the Halifax Explosion. The Hillis & Sons Foundry is the building on the left” Source: BiblioArchives / LibraryArchives from Canada via Wikimedia under a Creative Commons license


[1] Roger Marsters, “Collision in the Narrows: the 1917 Halifax Harbor Explosion,” National Maritime Historical Society, accessed November 29, 2023, https://seahistory.org/wp-content/uploads/SH160-14-18-Halifax.pdf.

[2] “Explosion in The Narrows: The 1917 Halifax Harbour Explosion,” Maritime Museum of the Atlantic, accessed November 23, 2023, https://maritimemuseum.novascotia.ca/what-see-do/halifax-explosion.

[3] Steve Hendrix, “Two ships collided in Halifax Harbor. One of them was a floating, 3,000-ton bomb,” The Washington Post, December 6, 2017, https://www.washingtonpost.com/news/retropolis/wp/2017/12/06/two-ships-collided-in-halifax-harbor-one-of-them-was-a-3000-ton-floating-bomb/.

[4] Marsters, “Collision in the Narrows: the 1917 Halifax Harbor Explosion.”

[5] Julia Blakely, “The Great Halifax Explosion,” Smithsonian Libraries and Archives, November 30, 2017, https://blog.library.si.edu/blog/2017/11/30/great-halifax-explosion/.

[6] “Mont Blanc Anchor Site,” Canada’s Historic Places, accessed December 2, 2023. https://www.historicplaces.ca/en/rep-reg/place-lieu.aspx?id=2582.

[7] John U. Bacon, The Great Halifax Explosion: A World War I Story of Treachery, Tragedy, and Extraordinary Heroism (New York: HarperCollins Publishers, 2017), 72.

[8] Marsters, “Collision in the Narrows: the 1917 Halifax Harbor Explosion.”

[9] Hendrix, “Two ships collided in Halifax Harbor. One of them was a floating, 3,000-ton bomb.”

[10] “A Vision of Regeneration,” Nova Scotia Archives, accessed November 29, 2023, https://archives.novascotia.ca/explosion/.

[11] “A Vision of Regeneration.”

[12] Blakely, “The Great Halifax Explosion.”