On the morning of December 6, 1917, the Canadian port city of Halifax became the site of a cataclysm caused as much by paperwork and protocol as by physical collision. The French cargo vessel SS Mont-Blanc was loaded to the brim with over 2,900 tons of high explosives, including picric acid, TNT, and volatile benzol fuel. Under normal maritime laws, a ship carrying dangerous cargo was required to fly a red hazard flag to warn surrounding traffic.
However, strict World War I censorship and security protocols created a fatal catch-22: military authorities ordered the Mont-Blanc to hide its deadly manifest to prevent enemy sabotage, leaving other captains completely unaware of the floating powder keg in their midst. Meanwhile, the Norwegian relief ship SS Imo was departing Halifax. Delayed by bureaucratic clearance inspections the previous evening, the Imo was operating behind schedule.
To make up for lost time, its captain navigated down the wrong side of the narrow harbor channel at excessive speed. When the Mont-Blanc and the Imo spotted each other on a collision course, both captains exchanged confusing whistle signals. Unaware of the Mont-Blanc's volatile cargo because of the missing manifest flags, the Imo refused to yield the right-of-way in time.
The resulting low-speed bump crumpled the Mont-Blanc's hull, igniting crushed benzol drums on the deck. Twenty minutes later, the ship detonated with the force of nearly three kilotons of TNT, flattening a square mile of the city and leaving nearly 2,000 dead.