Survivor of the deepest sub rescue in history calls the missing Titanic sub ordeal 'horrendous' and says he has 'a horrible feeling' about it

• A survivor of the deepest underwater rescue said he has a "horrible feeling" about the missing sub.
• "That is horrendous," Robert Mallinson told Sky News of the Titan submersible that vanished Sunday.

One of two men who survived the world's deepest underwater rescue on record said he fears the worst for the five people on board the submersible that vanished as it was headed to the shipwreck site of the RMS Titanic in the depths of the North Atlantic.

Former British Royal Navy pilot Roger Mallinson, who was saved in a dramatic rescue in 1973 along with his late co-pilot Roger Chapman after their submersible sank more than 1,500 feet below sea level off the coast of Ireland, told Sky News that he has a "horrible feeling" about the missing sub called Titan.

"That is horrendous," Mallinson, 85, told the news outlet when asked about the OceanGate Expeditions sub that lost communication with its mothership on Sunday, less than two hours into its journey to the wreck site of the iconic passenger liner that sank in 1912.

"I can't understand why they haven't transmitted some signal of some sort," said Mallinson. "I have a horrible feeling that something might be seriously wrong that they aren't able to transmit a signal."

Mallinson added, "I would have thought a hammer on a bit of the hull somewhere would be a good transmitter, and it would carry."

An extensive search-and-rescue effort has been underway to try to locate the 21-foot vessel. It is not clear how close the submersible was to the Titanic wreck — which lies 12,500 feet deep at the bottom of the ocean floor off the coast of Newfoundland, Canada.

That's roughly eight times deeper than the Pisces III vessel went when it sank nearly 50 years ago while Mallinson and Chapman were on board.

"I don't think anybody's ever attempted a rescue at this sort of depth," Stefan Williams, a professor of marine robotics at the University of Sydney whose lab works with uncrewed submersibles, told Insider on Wednesday.

Williams said rescue teams will be "trying to figure out as they go how they might do this if they do find" the missing Titan submersible.

Mallinson and Chapman were on a dive to lay transatlantic telephone cables on the seabed about 150 miles southeast of Cork, Ireland, when disaster hit and a hatch broke off the rear compartment, plunging the Pisces III to 1,575 feet below sea level.

The two men were trapped in the small submersible for more than three days before they were ultimately rescued with just 12 minutes of oxygen left, according to the BBC.

"It took 84 hours to rescue us," Mallinson told Sky News. "We didn't have enough food. We didn't have enough oxygen."

"We just had to really be rationing everything and look after each other," he added. "And I think we looked after each other, and that was a major, major lifesaver."

Mallinson also told Sky News that "luckily" before the dive, he stole a bottle of oxygen, and he credited that with saving their lives.

"Because we stole it, I'm still here, otherwise we certainly wouldn't have been," he said.

The Pisces III was finally hauled to the surface on September 1, 1973, by the cable ship John Cabot, and it remains the deepest successful underwater rescue in history, according to Guinness World Records.