OceanGate's Titan submersible imploded on its way to the Titanic wreck one year ago. The Coast Guard initially had 12 months to complete its investigation, but says it needs more time.

The Navy, which was part of the unified command hunting for the Titan submersible, said it had acoustic data "consistent with an implosion" on Sunday at the start of a five-day search.

The five people who died while trying to catch a glimpse of the wrecked ocean liner included a Guinness World Record holder, a deep sea entrepreneur, wealthy businessmen and "Mr. Titanic."

After days of search and rescue efforts, U.S. Coast Guard officials have determined there was a "catastrophic implosion of the vessel," and that all on board died.

Experts from within and outside OceanGate worried about the safety and development of the Titan as far back as 2018, years before its inaugural dive. One tells NPR its disappearance isn't a surprise.

The U.S. Coast Guard said that a surveillance plane detected "underwater noises" close to where the Titan lost contact with its control room. Experts say the sub's oxygen may run out on Thursday.

The Titan, a minivan-size submersible, was carrying five people to the Titanic's watery grave when it lost contact. The vessel has enough oxygen to keep its passengers alive for about 40 more hours.

The Titanic wreck is hard to reach and harder to capture, with most images showing just a section at a time. The first full-sized digital scan offers what experts call a game-changing view.