(Web Desk) - The 'banging' sound that kept the hopes of families and rescuers alive in the search for the doomed Titan submersible has been revealed for the first time in chilling new audio.
A desperate search for the sub was launched after it lost contact with its mothership and vanished during an expedition to the Titanic wreck on Sunday June 18, 2023.
After an agonising wait for news, late into the second day of searching, reports emerged that banging noises were detected in 30-minute intervals, deep under the ocean.
Played for the first time in a new documentary, the hollow sound has a regular, steady beat which caught the attention of experts - and sparked hopes that the noise could be SOS signals being made by the five men on board.
'It could be somebody knocking, the symmetry between those knockings is very unusual,' former Navy Submarine Captain Ryan Ramsey tells the documentary.
'It's rhythmic, it's like somebody is making that sound, and the fact that it is repeated is really unusual.'
After the sound was first recorded at around 11.30pm on June 20, the US Navy confirmed that it had detected the noises the next morning.
Coast Guard Captain Jamie Frederick admitted at the time: 'With respect to the noises, specifically, we don't know what they are, to be frank with you.'
The world was gripped as rescuers urgently doubled their efforts to track down the missing sub before oxygen was expected to run out.
There were five passengers on board; Tourists Hamish Harding, 58, Shahzada Dawood, 48, and his son Sulaiman Dawood, 19, French Navy pilot Paul-Henry Nargeolet and OceanGate CEO Stockton Rush.
Tragically, hopes raised by the mysterious knocking sound were later dashed.
The Pelagic search team's submersible, Odysseus 6K, reached the seafloor after days of searching and on June 22 found debris of the sub, around 1,600 feet from the bow of the Titanic.
Titan had imploded as a result of enormous water pressure bearing down on the vessel - killing everyone on board in what was likely a matter of milliseconds.
Now new documentary, which will be released to mark a year since the tragedy in June, will go behind the scenes of the multi-million dollar search operation.
Minute by Minute: The Titan Sub Disaster details the events leading up to Titan's ill-fated expedition to the Titanic wreck.
The documentary, by ITN productions for Channel 5, also asks what lessons can be learned from the disaster.
It features the never-before-heard audio of the banging as well as expert opinion on what happened during the search mission that gripped the world.
At the time, some experts warned against taking the sound as evidence of life.
Many claimed that the noise was likely to be 'debris' and 'junk' from the iconic wreck.
Jeff Karson, Professor Emeritus of Earth and Environmental Sciences at Syracuse University, said at the time that the sounds heard were likely to be 'wishful thinking' by the US Coast Guard.