Runic was built for the White Star Line as a livestock carrier, serving the Liverpool - New York route. She was sold in 1895 to the West India & Pacific Steamship Co. and renamed Tampican. In 1899 she was transferred to the Leyland Line. In 1912, she was sold to Moss & Co. and immediately sold again to the South Pacific Whaling Co. Renamed Imo, her new owners employed her as a whale oil tanker. In 1917, whilst servings as a 'Belgian Relief Ship', she collided with the French vessel Mont Blanc in Halifax Harbour (Nova Scotia).

Imo had left its mooring in Bedford Basin and was headed for the open sea. At about the same time, the French ship Mont Blanc was moving up the harbour to moor. Mont Blanc, a much smaller vessel (said to be barely seaworthy), was waiting for an eastbound convoy so that she could cross the Atlantic in greater safety - the threat from German submarines at that time made the convoy system a necessity. She was carrying 35 tons of benzol, 300 rounds of ammunition, 10 tons of gun cotton, 2,300 tons of picric acid (used in explosives), and 400,000 pounds of TNT.  These munitions filled her holds and cargo spaces and even her decks were stacked with potentially lethal cargo.

Despite being, in effect, a gigantic floating bomb Mont Blanc was not flying any signal flag(s) to indicate her dangerous burden. Confusion arose when Imo and Mont Blanc had to pass each other; the former White Star ship was travelling fast and too close to Dartmouth when the Mont Blanc's captain became aware of the approaching problem; he signalled that his vessel was in her correct channel. But Imo signalled that she was intending to bear further to port - even closer to Dartmouth and further into the Mont Blanc's channel. Mont Blanc signalled again that she was still intending to pass to starboard; she was by this time very close to the Dartmouth shore and travelling dead slow.

Mont Blanc's captain was faced with a choice between steering uncomfortably close to the shore or going across Imo's bow to pass on her opposite side, he opted for the latter course. Perhaps both ships simultaneously decided that there was a real danger of collision - as Mont Blanc sailed in front of Imo, each of them rang up Full Astern. In the process, Imo's bow swung towards Mont Blanc and clipped her - missing the TNT, but striking the picric acid stored directly beneath the drums of benzol on deck. The impact cut a wedge in Mont Blanc's side and produced sparks.

The crew of Mont Blanc, seeing flames licking around their volatile cargo, immediately boarded the lifeboats, shouting warnings that no one heeded or understood. They rowed for Dartmouth, leaving the now furiously burning ship to drift towards Halifax, propelled in that direction by the push from Imo.

Mont Blanc drifted by a Halifax pier, brushing it and setting it ablaze. Members of the Halifax Fire Department responded quickly; they were connecting their engine to the nearest hydrant when Mont Blanc disintegrated in a blinding white flash, creating the biggest man-made explosion before the nuclear age. Because it took the blazing vessel 20 minutes to erupt, there was time for sight-seers to gather and for people living nearby to open their windows and satisfy their curiosity.  The majority of them were killed outright; like many of the men claimed by shellfire during that 'War To End All Wars', those firefighters and citizens were sometimes smashed into atoms by the merciless, killing ferocity of the explosion.      

The blast flattened Richmond (north end of Halifax). The shock wave was felt up to 270 miles (430 km) away (it was noticed in Sydney, Cape Breton). The casualty figures were appalling. At least 2,000 people were killed; another 2000 were listed as missing and never found; 9,000 were injured (including 1,000 people who sustained eye damage) and 25,000 were made at least temporarily homeless. Over 1,600 buildings in a 16 mile (26 km) radius were destroyed and 12,000 more damaged. The total property loss was estimated at $35,000,000. Some of the damage was the result of a 13 foot (3.96 m) tidal wave generated by the explosion - this  wall of water not only struck buildings and people, it also assailed shipping in the port - even armoured warships were battered.

The Mont Blanc was completely destroyed - she was ripped apart and scattered like metal rain. Some of her heavier parts flew through the air for great distances and added to the death and destruction. Despite being  grounded,  the Imo survived the disaster with only superficial damage.

In 1918 the Imo was renamed Guvernoren. On 30th November 1921, en route from Norway to Antarctica, still under the ownership of the South Pacific Whaling Co., she ran aground on rocks off Port Stanley (the Falkland Islands) in a heavy fog and was declared a total loss.