The U.S. Coast Guard announced via Twitter early Thursday that a remotely operated vehicle (ROV) deployed by the Canadian vessel Horizon Arctic has reached the sea floor, beginning its search for the missing submersible.

Meanwhile, the French vessel L'Atalante is preparing its ROV to enter the water in the search area, the U.S. Coast Guard said.

Time is running out as rescuers race to locate and save five people trapped in a submersible that vanished during a tour of the Titanic wreckage on Sunday morning.

The deep-sea vessel submerged at 8 a.m. ET on Sunday with a 96-hour oxygen supply, according to the U.S. Coast Guard. That amount of breathable air is forecast to run out on Thursday morning.

The search and rescue mission remains ongoing.

The New York Times traced the lineage of Wendy Rush, wife of missing OceanGate CEO Stockton Rush, and found that she's the great-great-granddaughter of a couple who died on the Titanic, Isidor and Ida Straus.

The executive director of the Straus Historical Society told ABC News that The Times article, which cites archival records, is largely correct with regard to Wendy Weil Rush's heritage.

-ABC News' Nic Uff

A U.S. Navy portable crane system capable of bringing up items from as deep as 20,000 feet has arrived in St. John's, Newfoundland, but is waiting to be welded onto a chartered ship to take it to the search area for the missing submersible, according to a U.S. Navy official.

The Navy has not yet contracted a ship for the salvage system, known as Fly Away Deep Ocean Salvage System or FADOSS, the official told reporters Wednesday. Once the ship is contracted, Navy teams will spend approximately 24 hours working around the clock to weld the system aboard the ship before it can leave port, the official said.

FADOSS is the salvage system the U.S. Navy uses for all of its deep-water recoveries. Last year, it was able to bring up an F/A-18 aircraft that had fallen into the waters of the Mediterranean Sea.

-ABC News' Luis Martinez

The United States Coast Guard commander leading the search for a missing submersible off the coast of Newfoundland, Canada, said Tuesday morning that crews in multiple aircraft have flown over an area of the Atlantic Ocean "roughly about the size of Connecticut" while "looking for any signs of surfacing."

"As we continue on with the search, we're expanding our capabilities to be able to search under the water as well," Rear Adm. John Mauger, commander of the First Coast Guard District, told ABC News' Robin Roberts during an interview on "Good Morning America."

A commercial vessel with remotely operated vehicles is now on scene that will allow rescuers to search underwater, according to Mauger.

"This is a complex case," he added. "The Coast Guard doesn't have all the resources to be able to affect this kind of rescue, although this is an area that's within our search zone."

In many cases, Mauger said, the Coast Guard's role is to coordinate all of the assets and technical expertise that can be used in a search, in addition to operating aircraft or ships when necessary.

"In this particular case, we've established a unified command with the United States Navy, with the Canadian Armed Forces, with the Canadian Coast Guard and with the private operator OceanGate Expeditions to make sure that we understand what's needed and deploy all available equipment to the scene that could be used to locate this submersible, whether it's on the surface or down beneath the surface," he said.

Crews have been working "around the clock" to locate the deep-sea vessel since it lost contact with its operator on Sunday morning, according to Mauger.

In the last 24 hours, a Canadian aircraft has been dropping sonar buoys into the water that can pick up sound the submersible may be emitting. Vessels that have the capability to listen with their own sonar equipment are also on scene, according to Mauger.

"If they are making sound, that's certainly one of the ways that we're going to use to locate them," he said.