The Department of Defense is refusing to say whether it notified families of the passengers on the Titan submersible after detecting a possible implosion noise immediately after the vessel lost contact with its mother ship.

In a statement to Fox News Digital, the U.S. Coast Guard, which led the Pentagon’s unified command for the incident, said it had contacted families when it became aware of the situation and notified them once debris was found days later. However, officials said Thursday, after the debris was found, the U.S. Navy had detected an implosion noise almost immediately after the Titan lost contact on June 18.

“The Unified Command contacted the families as soon as we were aware of the incident, and we have maintained contact throughout our response,” Coast Guard spokesperson Anne McGoldrick told Fox News Digital.

“As has been our focus through this search, and is policy within the Search and Rescue community, officials will always notify Next of Kin and make every effort to involve the family before information is released to the public,” McGoldrick said. “The families were immediately notified as soon as the debris was identified.”

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Portraits of the five crew members of the missing OceanGate Titan sub

Inset, from left: Suleman Dawood, Shahzada Dawood, Stockton Rush, Paul-Henry Nargeolet and Hamish Harding were aboard the OceanGate Titan submersible. (Engro Corp. | Reuters/Shannon Stapleton | @OceanGateExped/Twitter | Felix Kunze/Blue Origin via AP | Ocean Gate/Handout/Anadolu Agency via Getty Images)

It remains unclear whether U.S. officials leading the incident response ever notified families on June 18, or in the four subsequent days, that an implosion likely occurred. The Coast Guard, Navy and Department of Defense didn’t respond to follow-up questions from Fox News Digital.

On June 18, the five passengers of the Titan, a submersible managed by exploration company OceanGate, boarded the vessel to dive for a viewing of the Titanic about 900 miles east of Massachusetts. The passengers were OceanGate CEO Stockton Rush; British businessman Hamish Harding; Pakistani father-and-son Shahzada and Suleman Dawood; and Paul-Henry Nargeolet, a former French Navy officer and Titanic expert.

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Approximately an hour and 45 minutes into the dive, the Titan lost contact with the mother ship it had launched from. In the days following, the Coast Guard spearheaded a comprehensive search-and-rescue effort involving private sector and Canadian entities, and regularly updated the public on the estimated amount of oxygen left on board the Titan.

On Wednesday, the Coast Guard said it had heard “underwater noises” in the search area, which some believed to indicate the Titan was stuck below the surface with its passengers trapped.