A defense budget expert estimates once the U.S. military participation concludes, the cost for the search and rescue mission of the five passengers on board the Titan submersible will cost the U.S. around $1.5 million.

Mark Cancian, a senior advisor with the Center for Strategic and International Studies, came up with the estimate based on aircraft sorties, cross referencing the U.S. Department of Defense cost numbers, Coast Guard Cutter costs and flying hour costs. He said some costs have already been set aside in various budgets, with resources simply diverted to the site.

He emphasized that these are strictly well-informed guesses.

A spokesperson for the Coast Guard's District 1 in Boston would not give an estimate of costs so far, saying, "We cannot attribute a monetary value to Search and Rescue cases, as the Coast Guard does not associate cost with saving a life."

-ABC News' Jaclyn C. Lee

The U.S. Coast Guard will be the organization leading the investigation into the OceanGate sub incident.

The NTSB announced the news on Friday via Twitter, noting it will "contribute to their efforts."

A Las Vegas father and son told ABC News OceanGate CEO Stockton Rush pressured them for months into taking two seats on the now failed mission to the Titanic, making bold claims about the vessel's safety.

Financier Jay Bloom shared text messages between himself and Rush where Rush dismissed concerns from Bloom and his son Sean about taking the trip on the Titan submersible.

"While there's obviously a risk it's way safer than flying in a helicopter or even scuba diving," Rush texted.

"He sort of had this predisposition that it was safe," Bloom told ABC News. "And anybody who disagreed with him, he felt it was just a differing opinion."

Bloom added that Rush flew out to Las Vegas in a homebuilt plane to convince him to attend the voyage aboard the submersible.

"He flew it all the way to Vegas. And I was like, 'This guy is definitely down to take risk,'" Bloom said.

-ABC News' Sam Sweeney

The U.S. National Transportation Safety Board will be participating in the multiagency investigation into the Titan sub incident, an NTSB spokesperson told ABC News.

The U.S. agency joins the U.S. Coast Guard and the Transportation Safety Board of Canada (TSB), which deployed its members to St. John’s, Newfoundland and Labrador.

The TSB says it will conduct a "safety investigation regarding the circumstances of this operation conducted by the Canadian-flagged vessel Polar Prince."

-ABC News' Amanda Maile

Engro, the company sub passenger Shahzada Dawood worked as the vice chairman, offered its condolences for both Dawood and his son, Suleman Dawood, on Thursday.

"With heavy hearts and great sadness, we grieve the loss of our vice chairman, Shahzada Dawood, and his beloved son, Suleman Dawood," the company said in the message. "Our thoughts and prayers are with the Dawood family at this tragic time."

"We extend our heartfelt condolences to the family, colleagues, friends and all those around the world who grieve this unthinkable loss," it added.

-ABC News' Habibullah Khan