Five people were on board the OceanGate-owned submersible diving to the wreckage of the Titanic when contact was lost with the vessel on 18 June.
This prompted a frantic search effort that captured the the world's attention, during which a 'rhythmic' and 'unusual' banging noise was heard deep underwater.
The chilling bangs came in 30-minute intervals and came in pairs of two knocks with a regular hollow beat.
It was initially thought that the banging could be be a desperate SOS call from the vessel, giving officials hope that those on board may still be alive, and search teams doubled down on their efforts to track down the missing sub before oxygen ran out.
However, in time, it was concluded that the sub had imploded on the day it had gone missing — killing the five members on board instantly.
US Navy analysis later determined that the banging noises were most likely either ocean noise or noise from other search ships.
For the first time, audio from the Canadian Air Force of the banging has been released as part of The Titan Sub Disaster: Minute by Minute.
Former Navy Submarine Captain Ryan Ramsey tells the documentary: "It could be somebody knocking, the symmetry between those knockings is very unusual.
"It's rhythmic, it's like somebody is making that sound, and the fact that it is repeated is really unusual."
Rarely-seen footage from previous Titan expeditions has also be shared as Arthur Loibl — one of the first men to travel to the Titanic wreck in the submersible — describes what it feels like to be over two-miles underwater.
In the days that followed the implosion, the US coastguard found fragments of the vessel as well as some human remains in the area.
However, experts warned not to expect the bodies of the victims to be fully recovered due to the 'unforgiving environment' of the ocean.
Since the tragedy, OceanGate's website has said they have 'suspended all exploration and commercial operations' after being urged to reconsider taking the expeditions.
The two-part documentary creates a detailed picture of events surrounding the submersible's expedition, re-tracing its journey and asking what lessons have been learned from the disaster.
Brits can watch the documentary on 6 and 7 March at 9pm on Channel 5.
Topics: News, Channel 5, Documentaries
