A Canadian military surveillance aircraft detected underwater noises amid the search early Wednesday in a remote part of the North Atlantic for a submersible that vanished while taking five people down to the wreck of the R.M.S. Titanic.

A statement from the U.S. Coast Guard did not elaborate on what rescuers believed the noises could be, though it offered a glimmer of hope for those lost aboard the submersible Titan as estimates suggest as little as a day’s worth of oxygen could be left if the vessel is still functioning.

Meanwhile, questions remain about how teams could reach the lost submersible, which could be as deep as about 12,500 feet below the surface near the watery tomb of the historic ocean liner. 

Newly uncovered allegations also suggest there had been significant warnings made about vessel safety during its development.

Lost aboard the vessel are its pilot, Stockton Rush, the chief executive of the company leading the expedition. His passengers are a British adventurer, two members of a Pakistani business family, and a Titanic expert.

The Coast Guard wrote on Twitter that a Canadian P-3 Orion had “detected underwater noises in the search area.” Searchers then moved an underwater robot to that area to search. However, those searches “have yielded negative results but continue.”

“The data from the P-3 aircraft has been shared with our U.S. Navy experts for further analysis which will be considered in future search plans,” the Coast Guard said.

The Coast Guard statement came after Rolling Stone, citing what it described as internal U.S. Department of Homeland Security emails on the search, said that teams heard “banging sounds in the area every 30 minutes.”

In underwater disasters, a crew unable to communicate with the surface relies on banging on their submersible’s hull to be detected by sonar. 

However, no official has publicly suggested that’s the case and noises underwater can come from a variety of sources.

Yet the reports have sparked hope in some, including the president of the Explorers Club, Richard Garriott de Cayeux. 

He wrote an open letter to his club’s adventurers, who include the missing British man and the Titanic expert aboard the Titan, that they had “much greater confidence” now after they spoke to officials in Congress, the American military and the White House about the search.

Three C-17 transport planes from the U.S. military have been used to move commercial submersible and support equipment to St. John’s, Newfoundland, from Buffalo, New York, to aid in the search, the U.S. Air Mobility Command said.

The Canadian military said it provided a patrol aircraft and two surface ships, including one that specializes in dive medicine. It also dropped sonar buoys to listen for any sounds from the Titan.

Rescuers have been racing against the clock because even under the best of circumstances the vessel could run out of oxygen by Thursday morning.

In addition to an international array of ships and planes, an underwater robot had started searching in the vicinity of the Titanic and there was a push to get salvage equipment to the scene in case the sub is found.

Meanwhile, documents show that the company that oversaw the Titan‘s mission, OceanGate Expeditions, had been warned there might be catastrophic safety problems posed by the way the experimental vessel was developed.

OceanGate’s director of marine operations, David Lochridge, said in a 2018 lawsuit that the company’s testing and certification was insufficient and would “subject passengers to potential extreme danger in an experimental submersible.”

The company insisted that Mr. Lochridge was “not an engineer and was not hired or asked to perform engineering services on the Titan.” 

The firm also says the vessel under development was a prototype, not the now-missing Titan.