On June 18, it was reported that the underwater vessel - known as 'Titan' - disappeared after submerging into the depths of the North Atlantic Ocean during a tour of the well-known Titanic wreckage.
The expedition, operated by OceanGate, began in the early hours of Sunday morning, with the aim of diving to 12,500 feet to where the wreckage lays. However, after being unable to provide a signal to a Canadian research vessel just an hour and 45 minutes into the journey, operators grew concerned.
Three days later and there has been no sign of the submersible, which was carrying five people at the time of its disappearance. A major search operation is currently underway, headed by the US Coast Guard as well as OceanGate Expeditions.
As reported by Sky News, regular banging sounds were picked up by a Canadian P-3 aircraft using sonobuoys - a special type of buoy with underwater sonar capabilities - after it was deployed in the search for the missing vessel.
This discovery was shared by Department of Homeland Security leadership via an internet email - obtained by Rolling Stone - which stated that the crews heard the sounds in 30-minute intervals while scouring where the sub's five passengers disappeared.
"RCC Halifax launched a P8, Poseidon, which has underwater detection capabilities from the air," the DHS email read, per the outlet. "The P8 deployed sonobuoys, which reported a contact in a position close to the distress position. The P8 heard banging sounds in the area every 30 minutes. Four hours later additional sonar was deployed, and banging was still heard."
The email does not disclose what might have caused the banging sounds, but, another email obtained by CNN revealed the discovery of additional "acoustic feedback".
"Additional acoustic feedback was heard and will assist in vectoring surface assets and also indicating continued hope of survivors," the email said, according to the publication.
However, the US Coast Guard took to their social media on Wednesday (June 20) to inform people that the investigation of the noises by specialist underwater equipment had "yielded negative results".
News of the banging noises comes after a press conference by U.S. Coast Guard Captain Jamie Frederick on June 20, where he announced that the submersible could have an estimated "40 hours of breathable air left". This is based on an earlier estimate that the submersible embarked on its mission with an initial 96 hours of available oxygen, per CBS News.
As of this writing, that means the oxygen supply is around the 30-hour mark.
As the terrifying search continues, authorities are making every effort to locate the missing submarine. "We will do everything in our power to affect a rescue," pledged Frederick, adding: "There is a full-court press effort to get equipment on scene as quickly as we can."
The five confirmed names on the missing submersible are CEO and founder of OceanGate Expeditions Stockton Rush, British billionaire explorer Hamish Harding, French submersible pilot Paul-Henri Nargeolet, Pakistani businessman Shahzada Dawood and his 19-year-old son Suleman Dawood.
OceanGate Expeditions - the company that hosts a Titanic Expedition to the historic site - issued a statement to PEOPLE, which read: "Our entire focus is on the crewmembers in the submersible and their families."
"We are deeply grateful for the urgent and extensive assistance we are receiving from multiple government agencies and deep-sea companies as we seek to reestablish contact with the submersible. We pray for the safe return of the crew and passengers," they added.
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