LONDON -- Everybody knows why the Titanic went down. She hit an iceberg and despite being supposedly designed as unsinkable, she sank and took 1,500 lives with her.

But that, as the film makers of a new documentary say, is not the whole story.

The whole story involves a fire that had been smoldering for days in one of the vessel’s coal storage bunkers, a fire whose heat may have severely weakened the ship and hastened its sinking.

Senan Molony CBS News

The new theory comes from recently discovered old photos of the Titanic’s launching.

Irish journalist Senan Molony has been working the fire theory for years.

He says a dark patch on the Titanic’s hull shows the coal was burning even as the ship was being launched.

“The intensity of the fire not only weakened a forward bulkhead, but also may have caused a serious deformity to the hull,” Malony said.

“The ship was put to sea with an out of control fire that required 12 men to try to tackle it for most of her maiden voyage.”

The dark patch on the hull was weakened by coal fires, according to a new report CBS News

The coal fire was known about at the time and was dismissed as a cause of the disaster by the official inquiry that followed it. The smoldering fuel was dug out and burned in the ships boilers.

But Molony says the need to get rid of that burning coal quickly may have been one of the reasons Titanic kept going at top speed, despite knowing there were icebergs around.

Almost 105 years later there’s still enough doubt, and interest, to keep the story of the world’s most famous maritime disaster alive.

“Titanic: The New Evidence” airs Saturday, Jan. 21 at 8 p.m. ET/PT, on the Smithsonian Channel, a division of CBS.