- By Kathryn Armstrong & Gareth Evans
- BBC News
The search for a missing submarine near the wreck of the Titanic has been diverted after noises were heard in the area.
A Canadian P-3 aircraft – using sonar buoys – picked up sounds underwater, which US Navy experts are now investigating.
Crews were investigating the source of Wednesday’s noise in a remote area of the North Atlantic.
A day’s worth of oxygen is limited if the vessel remains intact.
The US Coast Guard did not provide further details on what the noise was. According to an internal US government memo seen by multiple media outlets, the thunder was heard at 30-minute intervals on Tuesday.
Additional sonar was deployed four hours after the sounds were first detected, and the noise is still being heard, officials said.
Remotely operated vehicles (ROVs) have been sent to the area, but nothing more has been found.
Deep-sea experts told the BBC it was difficult to determine what the noises could be without looking at the data – and the commander leading the search confirmed the source was unknown.
Chris Brown, an investigator and friend of one of the group, said he believed the reported thunder sounds could be them.
“If you keep making noise, it won’t pick up, but doing it every 30 minutes is instructive to humans,” he told the BBC. “I’m sure they’re all conserving oxygen and energy because it’s cold and dark out there.”
More on Titanic Sub
There were five people on board when the communication was lost for an hour and 45 minutes on Sunday. At that time it was probably more than halfway towards the Titanic’s wreckage, or about 1,900 m (6,233 ft) below the surface.
Search officials estimate that the supply will run out by about 10:00 GMT (06:00 EDT) on Thursday, meaning the ship could have less than a day’s worth of oxygen if it remains intact.
The five people on board were British businessman Hamish Harding, 58, British-Pakistani businessman Shahjata Dawood, 48, and his son Suleman, 18, French explorer Paul-Henri Narcolet, 77, and Stockton Rush, 61.
Mr Rush is chief executive of Oceangate, which owns the Titanic and runs tours of the Titanic wreck.
The team was sealed inside the sub using external bolts, meaning they couldn’t escape it even if it reappeared.
The search operation has yet to locate, but is expanding to include additional resources and rescue expertise from private agencies.
The mission is complicated – there is no communication from OceanGate’s Titan companion, and light cannot penetrate that far, so visibility is quickly lost below the water’s surface.
Bad weather remained in the area, although the US Coast Guard said these had improved on Tuesday.
With an area of 7,600 square miles (19,683 sq km), it is larger than the US state of Connecticut.
“Our crews are working around the clock to make sure we’re doing everything we can to locate Titan and the five crew members,” Coast Guard Capt. Jamie Frederick said earlier.
US and Canadian agencies, navies and commercial deep-sea companies all assist in the operation, which is operated out of Boston, Massachusetts. This includes the use of military aircraft and submarines, as well as sonar buoys dropped from aircraft or ships on the ocean surface for underwater acoustic research.
During her maiden voyage from Southampton to New York in 1912, the Titanic hit an iceberg. More than 1,500 of the 2,200 passengers and crew on board died.
Its ruins have been extensively explored since their discovery in 1985.
OceanGate Expeditions charges guests $250,000 (£195,270) to see the famous wreck on its eight-day cruise.