On 6 December 1917, Stella Maris, with Captain Horatio Harris Brannen and 23 others aboard, was towing two scows near mid-channel in the Narrows of Halifax Harbour leading into Bedford Basin. Shortly before the explosion, the tug had to hastily change course to avoid the outbound which was departing Bedford Basin. Imo then collided with Mont Blanc, a French munitions ship. The collision started a fire on Mont Blanc, forcing the crew to evacuate. The burning ship then began drifting towards Halifax's Pier 6 on the western shore. Stella Maris anchored its barges to respond to the fire and approached the burning munitions ship, spraying the flames with its fire hose. As the fire was too intense to stop with a single fire hose, the Stella Maris's crew began to prepare a towline to pull the French vessel away from Pier 6 and prevent the fire from spreading ashore. The crew were in the process of retrieving a ten-inch hawser from the hold to assist a party of volunteers from 's steam pinnace in securing a line to Mont Blanc. Before this could be done, the explosion occurred.