The leader of a team that was sent down to attempt to rescue the OceanGate Titan submersible teared up as he described the moment that their rescue mission became a recovery operation.

The Titan is believed to have suffered a ‘catastrophic implosion’ on 18 June, as it was making a descent to the wreck site of the RMS Titanic, some 12,500 feet beneath the Atlantic Ocean.

That implosion would have almost instantly killed anyone on board the craft, which had five passengers at the time.

OceanGate CEO Stockton Rush, father and son Shahzada and Suleman Dawood, French diver Paul-Henry Nargeolet, and British billionaire Hamish Harding are now believed to be dead.

Becky Kagan Schott/OceanGate

Pelagic Research Services were among those who attempted to rescue the submersible, in the event that it had simply become stuck or lost power.

It was believed that there could have been as much as 96 hours of emergency oxygen on board the Titan, meaning that it was perceived as a race against time.

Pelagic CEO Ed Cassano said: "We were always conscious of the crew of the Titan.

"Plain and simple, we were focused on rescue.”

However, once they arrived at the site of the Titanic wreck using the Odysseus 6K remote operated vehicle, they quickly realised it was no longer a rescue mission.

"Shortly after arriving on the seafloor, we discovered the debris of the Titan submersible... by 12 o'clock, a rescue turned into a recovery," Cassano said.

Speaking while close to tears, he explained that his whole team were working through ‘a lot of emotions’ after the disaster.

Cassano called for everyone else to see the ‘seriousness of the event’ and ‘respect the range of emotions’ of those involved in the mission.

Debris was found around 1,600 feet from the Titanic wreck on the ocean floor, at a depth of 12,500 feet.

The US Coast Guard has also said that what they presume to be human remains have also been recovered from the debris that was found.

Sky News

The nature of those possible remains has not been shared or specified.

Serious safety concerns had been raised before the Titan imploded, and now questions are being asked not only about Rush’s company, but also the safety of private submersible travel.

A full investigation has been ordered, with representatives from the USA, Canada, France, and the UK involved.

They’ll attempt to ascertain what happened leading up to the Titan’s demise, as well as establishing whether criminal or civil proceedings will be allowed.

OceanGate has previously refused to comment on the matter, but did release a statement paying tribute and mourning the victims.