Robert Ballard, who discovered Titanic wreck, said authorities 'immediately knew' where to look when they heard the Titan's implosion, but it took days for an ROV to get there

• Robert Ballard said the Coast Guard knew where to look for the missing Titanic sub.
• But the ROVs needed to explore the area took days to arrive, delaying confirmation of the tragedy.

Robert Ballard, a retired Navy officer who discovered the Titanic shipwreck in 1985, said the US Coast Guard knew exactly where to look for the missing Titanic sub but that it took the remotely operated vehicles needed to explore the area days to arrive, causing a delay in confirmation that the vessel imploded just hours after it began its mission Sunday.

During a Friday appearance on Good Morning America, George Stephanopoulos revealed that Ballard said once he heard the sub went missing, he knew this would be the outcome.

How was he so sure? Ballard said, "We are very familiar with exploring wrecks like this," adding that he explored the Scorpion submarine that imploded in 1968 just east of the Titanic wreck.

"We detected its implosion with our underwater listening system, and that's what the Navy told the Coast Guard the moment it happened. They picked up the implosion, passed it on to the Coast Guard, so we immediately knew where to go and where to look, but it just took time to get the ROVs down there, and they finally got there yesterday," Ballard said.

The sub went missing on Sunday after an hour and 45 minutes into its dive to the Titanic wreck, which sits on the ocean floor in multiple pieces at nearly 13,000 feet deep, when it lost all communications with its mother ship.

The US Coast Guard began a comprehensive search for the missing vessel on Monday afternoon, and it announced Thursday that an ROV had found debris near the wreck consistent with pieces of the missing sub, meaning it likely imploded just hours into its mission.

Later Thursday, the Wall Street Journal reported that the US Navy, using a top-secret listening system, actually heard the sound of an implosion hours after the sub went missing and that officials had thought it could have been the Titan.

The five people on board the sub are all presumed to be dead.