Crews remain hopeful as they continue to search for theTitan, a submersible carrying five passengers that disappeared in the Atlantic on Sunday.During a press conference in Boston on Wednesday, United States Coast Guard Captain Jamie Frederick confirmedprevious reportsthat suggested a Canadian P-3 “detected underwater noises” while searching the area.Frederick said “several P-3 flights heard noises” in the area, but that an initial ROV search of the area “yielded negative results.”But crews are not giving up in their search for the missing submersible, which likely hasless than 24 hoursof breathable oxygen left.“This is a search and rescue mission 100 percent,” Frederick told reporters.“We need to have hope, but I can’t tell you what the noises are,” the captain said Wednesday. “But I can tell you — and this is the most important point — we are searching where the noises are. And that’s all we can do at this point.”Alamy Stock PhotoTheTitanhas been missing since Sunday, when it lost contact with Canadian expedition vessel Polar Prince about 1 hour and 45 minutes into the dive, according to authorities.PEOPLE has confirmed the passengers on the vessel are Pakistani businessman Shahzada Dawood, his son Suleman Dawood, OceanGate CEO Stockton Rush,Titanicexpert Paul-Henri Nargeolet and British billionaire Hamish Harding.The “banging noises” werefirst citedin an internal email sent to the Department of Homeland Security leadership, whichRolling Stoneobtained on Tuesday. The DHS shared that crews heard the sounds in 30-minute intervals while searching where the sub’s five passengers disappeared.Alamy Stock PhotoAt Wednesday’s press conference, Frederick said a P-3 “heard some noises today, as well.”“We don’t know what they are, to be frank with you,” Frederick told reporters shortly before Hartsfield’s remarks. He also denied hearing that the sounds were heard in regular 30-minute intervals.Never miss a story — sign up forPEOPLE’s free daily newsletterto stay up-to-date on the best of what PEOPLE has to offer, from celebrity news to compelling human interest stories.Carl Hartsfield, Director and Senior Program Manager at the Woods Hole Oceanographic Institution, confirmed to reporters that the sounds were described as “banging noises.”However, it can be “very difficult to discern what those noises are at times,” Hartsfield said, noting that some sounds “can sound man-made to the untrained ear.”“I can assure you that the people who are listening to these tapes are trained,” he told reporters, later adding, “The team is searching in the right area.”OceanGate submersible Titan.Alamy Stock PhotoFrederick said crews are “grateful for the spectrum of international assistance that has been provided” for the search.Search crews have also been “in close contact” with both British and French consulates general and are working to assure “that their concerns are being addressed,” the captain added.Frederick reiterated that it is “exceptionally difficult” for crews to mobilize quickly in response to theTitan’s disappearance. Weather, currents and other factors are leading officials to expand the search area, complicating efforts to find the vessel, he added.Crews have now searched a surface area twice the size of Connecticut, according to the captain. He promised to continue to put forward “every available asset that we have” to find theTitanand its passengers.“When you’re in the middle of a search and rescue case, you always have hope,” Frederick told reporters. “That’s why we’re doing what we do.”

Crews remain hopeful as they continue to search for theTitan, a submersible carrying five passengers that disappeared in the Atlantic on Sunday.

During a press conference in Boston on Wednesday, United States Coast Guard Captain Jamie Frederick confirmedprevious reportsthat suggested a Canadian P-3 “detected underwater noises” while searching the area.

Frederick said “several P-3 flights heard noises” in the area, but that an initial ROV search of the area “yielded negative results.”

But crews are not giving up in their search for the missing submersible, which likely hasless than 24 hoursof breathable oxygen left.“This is a search and rescue mission 100 percent,” Frederick told reporters.

“We need to have hope, but I can’t tell you what the noises are,” the captain said Wednesday. “But I can tell you — and this is the most important point — we are searching where the noises are. And that’s all we can do at this point.”

Alamy Stock Photo

The Oceangate submersible Titan

TheTitanhas been missing since Sunday, when it lost contact with Canadian expedition vessel Polar Prince about 1 hour and 45 minutes into the dive, according to authorities.

PEOPLE has confirmed the passengers on the vessel are Pakistani businessman Shahzada Dawood, his son Suleman Dawood, OceanGate CEO Stockton Rush,Titanicexpert Paul-Henri Nargeolet and British billionaire Hamish Harding.

The “banging noises” werefirst citedin an internal email sent to the Department of Homeland Security leadership, whichRolling Stoneobtained on Tuesday. The DHS shared that crews heard the sounds in 30-minute intervals while searching where the sub’s five passengers disappeared.

The Oceangate submersible Titan

At Wednesday’s press conference, Frederick said a P-3 “heard some noises today, as well.”

“We don’t know what they are, to be frank with you,” Frederick told reporters shortly before Hartsfield’s remarks. He also denied hearing that the sounds were heard in regular 30-minute intervals.

Never miss a story — sign up forPEOPLE’s free daily newsletterto stay up-to-date on the best of what PEOPLE has to offer, from celebrity news to compelling human interest stories.

Carl Hartsfield, Director and Senior Program Manager at the Woods Hole Oceanographic Institution, confirmed to reporters that the sounds were described as “banging noises.”

However, it can be “very difficult to discern what those noises are at times,” Hartsfield said, noting that some sounds “can sound man-made to the untrained ear.”

“I can assure you that the people who are listening to these tapes are trained,” he told reporters, later adding, “The team is searching in the right area.”

OceanGate submersible Titan.Alamy Stock Photo

The Oceangate submersible Titan

Frederick said crews are “grateful for the spectrum of international assistance that has been provided” for the search.

Search crews have also been “in close contact” with both British and French consulates general and are working to assure “that their concerns are being addressed,” the captain added.

Frederick reiterated that it is “exceptionally difficult” for crews to mobilize quickly in response to theTitan’s disappearance. Weather, currents and other factors are leading officials to expand the search area, complicating efforts to find the vessel, he added.

Crews have now searched a surface area twice the size of Connecticut, according to the captain. He promised to continue to put forward “every available asset that we have” to find theTitanand its passengers.

“When you’re in the middle of a search and rescue case, you always have hope,” Frederick told reporters. “That’s why we’re doing what we do.”

source: people.com