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Main Page > City of Ruins > Countdown to Catastrophe

Countdown to Catastrophe

The voyage that would wreck a city began earlier that week in New York.

Dockworkers loaded the French vessel Mont-Blanc with its doomsday cargo of picric acid, TNT, guncotton and benzol. It was all headed for the war in France, but Mont-Blanc couldn't cross the U-boat-ridden Atlantic alone.

The freight manifest for Mont-Blanc is a recipe for a giant bomb.

Value in 1917 US$
TNT[?] 226,797 kg $240,750
Wet picric acid[?] 1,602,519 kg $2,230,999
Dry picric acid 544,311 kg $960,000
Guncotton[?] 56,301 kg $65,165
Benzol[?] 223,188 kg $104,376
Totals 2653,115 kg $3,601,290
Source: Ground Zero: A Reassessment of the 1917 Explosion in Halifax Harbour

On the night of December 1, Mont-Blanc slipped out of New York harbour by night and headed to Halifax to join a convoy. It flew no flags warning of its cargo: ship laden with explosives would be a prime target for German attack.

A Halifax pilot boarded the ship outside the harbour around 4:00 pm on Wednesday, December 5. Francis Mackey was an experienced harbour pilot.

But it was too late to enter: the anti-submarine nets had been closed for the night. Mont-Blanc's captain Aimé Le Médec had to stay at sea for one more night.

Inside the nets, in Bedford Basin, the Belgian relief ship Imo waited to head out in the morning. Coal for its boilers had arrived too late for it to leave that day. Now, Captain Haakon From was behind schedule.

Imo had no cargo on board. It was heading to New York to collect emergency supplies for civilians in war-torn Belgium. It carried a large sign on its side: "BELGIAN RELIEF." The sign was supposed to discourage German submarines, or U-boats, from sinking it as a military target.


was a 97.54 meter (320-foot) French merchant ship, under charter to the French government. It wouldn't have been doing such important and dangerous work if so many newer, faster ships hadn't been sunk by German U-boats.

Mont-Blanc's captain had tried to join a convoy in New York, where it had loaded its cargo, but was turned down. Officials said Mont-Blanc wouldn't be able to keep up with the fast convoys out of New York. Capt. Le Médec was sent to Halifax to try his luck there.


Imo was a former cattle carrier on the White Star Line. It was first called Runic. White Star's ships’ names all ended in -ic, including Olympic, Atlantic…and Titanic.

The Commission for Relief in Belgium had chartered Imo to bring relief supplies from New York. Its registry in a neutral country, Norway, meant it would be less susceptible to attack. It had plenty of room for supplies--at 131 meters (430 feet) it was much larger than Mont-Blanc.

Imo had already completed eight return trips between Europe and New York when it arrived in Halifax.

Did You Know

Red Cross: In 1917, the entire membership of the Red Cross's Halifax branch were women.

Page Feature: The Explosion Timeline

Dec. 1   Mont-Blanc leaves New York
Dec. 5 4:00 pm Mont Blanc arrives at sub nets
Dec. 6    
  07:30 am sub nets open, Mont-Blanc enters harbour; Imo weighs anchor
  08:10 am Imo heads for Narrows
  08:15 am Stella Maris leaves dockyard
  08:45 am Imo collides with Mont-Blanc; fire starts
  09:04:35 am Explosion (couple minutes) tsunami

Page Feature: Anti-submarine nets

One of the most effective elements of the German war effort was its submarine fleet of U-boats (for the German unterseeboot, or "undersea boats"). U-boats had devastated both military and civilian British and French shipping.

Like other Allied ports, Halifax set up floating nets at the mouth of its harbour to help protect itself from a stealth attack by the dreaded U-boats. Each morning a "gate" opened in each net to let friendly vessels through. As night fell--subs would have the best chance to slip in undetected in darkness--the gates closed.

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