A U.S. Navy acoustic system “detected an anomaly consistent with an implosion or explosion” near the last-known location of the doomed Titanic submersible just hours after the vessel began its voyage, defense officials told The Wall Street Journal. The Navy’s system began listening in as soon as the submersible lost contact with its mother ship, about an hour and 45 minutes into its two-hour descent. It picked up what was believed to be an implosion not long after its disappearance, the officials said. “While not definitive, this information was immediately shared with the Incident Commander to assist with the ongoing search and rescue mission,” a senior Navy official told the Journal in a statement. When asked about what information it received and how it was used in the rescue mission, the Coast Guard didn’t respond to requests for comment. The Navy’s statement said officials held out hope “to continue our mission as a search and rescue and make every effort to save the lives on board.” The acoustic system, which helps detect enemy submarines, is top secret, and the Navy asked the Journal not to reveal its name. The U.S. Coast Guard confirmed on Thursday that a “catastrophic implosion” killed all five passengers aboard the Titan instantly.