Deep water, high pressure: Why the Titanic sub search is so complex

The U.S. and Canadian coast guards have deployed aircraft, boats and sonar equipment in their race to locate Titan, the 21-foot tourist submersible that went missing Sunday morning with five people aboard on a dive to the wreck of the Titanic.

The daunting search mission covers the ocean’s surface — in case the submersible has come up but is unable to communicate — and the vast depths beneath. The mission poses unique challenges that are further complicated by the depths involved. Depending on Titan’s distance below the surface, the effort could be the deepest search and rescue mission ever attempted. A rescue effort would contend with limited visibility, extremely high pressure and an ocean floor crowded with pieces of Titanic’s wreckage that make sonar identification of Titan difficult. And the submersible’s limited oxygen supply makes the search all the more urgent.

The first task for responders — before embarking on any rescue mission — is to find the submersible. Its location and depth will have a significant impact on the ability of responders to deploy a vehicle to rescue those inside or attach a hoist to bring it to the surface. The craft last made contact with the Canadian research vessel Polar Prince about an hour and 45 minutes into its dive to the ocean floor on Sunday morning, and authorities still do not know whether it is on surface or submerged. The site where the submersible began its dive to the Titanic is some 370 miles off the Canadian coast. Titanic lies 12,500 feet down.

If the submersible is equipped with a drop weight, the crew could jettison that load — potentially allowing the vessel to float to the surface. But on Tuesday, Rear Adm. John Mauger, the U.S. Coast Guard commander leading the search, told ABC News that multiple aircraft had flown over an area of the Atlantic “roughly about the size of Connecticut” looking for the vessel. He advised caution, citing the complexity of the search operation, particularly if the focus moves underwater. “The Coast Guard doesn’t have all the resources to be able to effect this kind of rescue, although this is an area that’s within our search zone,” he said.

“We’re really just focused on trying to locate the vessel,” Mauger said in a separate interview with Fox News on Monday. The large-scale search involved numerous “assets” using visual, radar and sonar technologies, he said.

The aerial aspect of the search involves two Coast Guard C-130 aircraft as well as a Canadian P-8 aircraft, the Coast Guard said. According to Mauger, the P-8 aircraft also can drop sonar buoys to detect underwater sounds.

“Right now, we have the ability to detect sonar noise returns with the equipment we’ve returned out there,” he said. Active sonar transducers work by emitting signals into the water and receiving echoes from objects in the path of the signals, according to NOAA. On Tuesday morning, the Coast Guard announced that the total search area had been extended to 10,000 square miles and that a Canadian P-3 aircraft capable of conducting sonar searches had arrived on the scene.

According to the Coast Guard, the surface search being conducted simultaneously involves nearby boats as well as the Polar Prince, the Canadian research vessel that deployed the submersible.

Underscoring the challenges, on Tuesday, the British Ministry of Defense, which is not involved in the search, said reports suggested that the depths involved greatly exceed the capabilities of NATO’s submarine rescue system.

The Coast Guard said Monday it was hoping to undertake a more comprehensive search of the bottom of the ocean, but this requires specialized equipment that officials have yet to be able to deploy.

On Tuesday morning, Mauger said a commercial vessel with remotely operated vehicles capable of searching at depth had arrived at the scene.

“We don’t have equipment on-site yet that can do a comprehensive sonar survey of the bottom. But we’re working very closely with our partners within the federal government and within the Canadian armed forces, and with private resources to provide that capability,” Mauger said, without specifying what the technology would be.

One of the few submersibles capable of undertaking a search to such a depth is the U.S. Navy’s Curv-21, a 6,400-pound remotely operated vehicle that can work at a maximum depth of 20,000 feet, according to the Navy. That submersible is equipped with high-resolution cameras and sonar technology and uses an “umbilical cord” to connect to a surface vessel. The Navy describes it as “self-contained and flyaway transportable,” meaning it can be deployed worldwide.

In 2022, the Navy deployed the Curv-21 in a 37-day mission to recover the wreckage of an F-35 fighter jet from a depth of approximately 12,400 feet in the South China Sea. According to the U.S. 7th Fleet, the Curv-21 was able to attach a line to the jet to allow a ship to hoist it to the surface.

One of the deepest-ever rescue missions took place in 1973, when two British sailors were stranded in a 6-foot steel ball at the bottom of a 1,600 ft abyss in the Atlantic. The pair were rescued after three days by a U.S. Navy submersible, CURV III, which fixed a line to their submersible, allowing it to be lifted to the surface.

Titanic’s wreckage poses an additional challenge to sonar detection. “There’s a lot of debris on the bottom,” Mauger said Monday. “Locating an object on the bottom will be difficult.”

No light is able to reach the depth of the Titanic, meaning any visual search is limited, as electric lights can illuminate little more than 20 feet, retired Royal Navy Rear Adm. Chris Parry told Sky News on Tuesday. He said that ocean currents are so strong at that depth that they could push the submersible along the seabed and away from Titanic, further complicating the search.

“It’s utterly dark down there, and you have also got a lot of mud and other stuff getting swept up by the (vehicle’s) propulsors,” Parry said.

The depth also places enormous pressure on any equipment deployed to the ocean floor.

“It’s rather like being in space, the same degree of danger and the same degree of issues.”