File photo. The missing submersible, together with owner, Stockton Rush, seated crosslegged within the tiny underwater vessel.

By Jonathan Mason-June 22nd, 2023.

The search for the missing submersible Titan in the area where the ship Titanic lies on the seabed has reached a critical stage, since the device was lowered at 4:00 a.m. on Sunday, and now may have exhausted its 4-day (96 hour) supply of oxygen, so if  the sub is indeed still intact and afloat, it may only have little or no life-sustaining oxygen left.

It went missing over the wreck of the Titanic in a remote area of the North Atlantic on Sunday with a four-day oxygen supply for its crew of five.

And on Thursday many questions remained over how it could be recovered.

The minivan-sized submersible, which was owned and operated by the private company OceanGate Expeditions has not yet been found. If it is pinpointed, it will need to be reached by complex rescue equipment and then brought to the surface in a complex and difficult operation that would likely take several hours.

That would need to happen before the oxygen supply runs out and without damaging its structure or endangering those on board. The passengers cannot be released until the vessel is brought to the surface, because they are bolted in.

The condition of the vessel and its crew of five is unknown, but the US Coast Guard said the operation remains purposed as a rescue mission. “This is a search-and-rescue mission, 100%,” Captain Jamie Frederick told reporters on Wednesday.

There appeared to be a glimmer of hope after officials said undersea noises had been detected by Canadian search planes on Tuesday and Wednesday.

But it is still unclear what these were, and officials said they may not have come from the submersible. Remote-controlled underwater search vehicles (ROVs) were deployed to the area where the sounds were detected but are yet to find anything.

One of the ROVs, deployed from the Canadian vessel Horizon Arctic, reached the ocean floor early Thursday morning. Several more were expected to arrive at the site later in the day, along with more multi-national support.

A French research ship, the Atalante, also arrived in the area on Thursday morning and deployed its own ROV, the US Coast Guard said. That robot is capable of researching depths below the Titanic wreck, which lies about 12,500 ft (3,810m) below the surface, and has experience of surveying the Titanic.

The overall area of sea being scoured is about 26,000 sq km (10,000 sq miles), twice the size of the US state of Connecticut.  The reason for this is that the missing vehicle could have been carried away on oceanic currents and if it has resurfaced, it could be far from the original site of the Titanic.

Sources: BBC, news agencies.