Reuters reports that the five-person crew of the missing vessel, known as Titan, includes Hamish Harding, a British billionaire and adventure enthusiast, and OceanGate's founder and CEO, Stockton Rush.

It disappeared on Sunday while on an expedition to explore the Titanic shipwreck site after losing contact with the Polar Prince research ship, roughly 1 hour and 45 minutes after their dive began.

The submarine was last reported in the North Atlantic, approximately 900 miles east of Cape Cod, in a water body known to have a depth of about 13,000 feet. Search and rescue operations began shortly afterwards and are still underway. According to the BBC, the entire sub is bolted shut from the outside, so even if the vessel surfaces, the occupants cannot escape without outside assistance and could suffocate within the capsule.