00:00New evidence has been obtained by the U.S. Coast Guard investigating the Titan submersible disaster in June 2023.
00:07It captures the sound at the very moment the vessel imploded, 1,000 metres below the surface.
00:12It was on its way to view the wreck of the Titanic.
00:15Well, now a BBC documentary team has been given unprecedented access to the investigation.
00:21Our science editor, Rebecca Murrell, has more on that.
00:25It was a trip that turned to tragedy.
00:28A submersible heading to the Titanic, 3,800 metres down.
00:35But OceanGate's Titan sub suffered a catastrophic failure, killing all five people on board.
00:42They were British explorer Hamish Harding, Suleiman Dawood and his father, British-Pakistani businessman Jhazada Dawood, French diver P.H. Narjalee and Stockton Rush, OceanGate's CEO.
00:52The U.S. Coast Guard's Marine Board of Investigation is looking into the disaster.
00:59Footage they recently discovered from Titan's support ship has been submitted as evidence for their investigation.
01:05You will hear a noise that is external to the ship, or external to the room, I should say, and you will see their reaction to the noise.
01:12Stockton Rush's wife, Wendy, is waiting for messages from the sub as it nears the seafloor.
01:17What was that like?
01:25So at that point you said, what was that bang?
01:27What was that bang?
01:28I'm going to back it up and play it one more time.
01:30It sounds like a door slamming.
01:32It should be about five o'clock in your city.
01:36Yeah.
01:37What was that bang?
01:39The noise is a sound of Titan imploding, but moments later, Wendy Rush gets a message from the sub.
01:45Drop two weights.
01:50Tighten, drop two weights.
01:52She mistakenly seems to think everything's okay, but in fact it's taken longer for the message to arrive than the sound of the implosion.
02:00Everyone on board is dead.
02:04The US Coast Guard says it has also now identified the moment the sub started to fail.
02:09This is a full-scale model of the Titan submersible.
02:13At the front there's a titanium dome with a viewport.
02:17And at the rear is another dome covered by a tail cone.
02:20The passengers were in this middle section, the hull.
02:24It's made from carbon fibre, a material that's highly unpredictable at depth.
02:28The hull is five inches, 13 centimetres thick, and it's made up of multiple layers.
02:34But these layers can come apart.
02:37A known problem called delamination.
02:40The sub was fitted with multiple sensors.
02:43And in 2022, during Titan's 80th dive, they picked up a loud bang.
02:48Stockton Rush said the noise was probably the sub shifting in its frame.
02:52But analysis of the data now shows this was the layers of carbon fibre breaking apart.
02:59Every dive after this one was a disaster waiting to happen.
03:03Their system said there has been a fundamental change in the material of your carbon fibre, and it was no longer structurally sound.
03:10Delamination at DiVedi was the beginning of the end.
03:13And everyone that stepped on board the Titan after DiVedi was risking their life.
03:19Oceangate have told the BBC,
03:20The disaster happened in a split second, but the ramifications continue.
03:44The US Coast Guard will publish their full report in the coming months.
03:47Rebecca Morrell, BBC News.
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