An international search and rescue operation is under way in a remote patch of the Atlantic Ocean after Titan, a submersible vessel the size of a van, went missing on Sunday as it descended toward the wreckage of the Titanic.

Here are some facts about the unusual vessel, which lost contact with the surface with four passengers and a pilot aboard:

* OceanGate Expeditions says it designed Titan to carry up to five people to a depth of 4,000 meters (13,120 feet). The wreckage of the cruise ship Titanic sits on the ocean floor about 3,800 meters (12,500 feet) below the surface.

* Titan weighs 9,525 kg (21,000 lbs), and can travel at a speed of 3 knots (3-1/2 miles per hour) using electric thrusters. OceanGate says it is equipped with powerful LED lights, a sonar navigation system and high-end camera equipment. It has a single porthole.

* OceanGate says Titan has a life-support system that can keep five people alive for up to 96 hours.

* Titan's carbon-fiber walls are 5 inches (13 cm) thick, and the vessel is capped at each end with titanium domes, according to David Pogue, a CBS News journalist who traveled on Titan last year. He had to sign a liability waiver describing the vessel as "experimental" and acknowledging a risk of injury or death.

* Once passengers are inside, the hatch is bolted shut. Passengers generally sit on the floor, leaning their backs against a curved wall. There is a rudimentary toilet aboard.

* It is launched from a small platform that can be carried out to sea aboard a commercial ship and submerged a few dozen meters below the surface.

* The vehicle is operated using a video-game controller, media have reported. OceanGate workers on the surface ship track the location of Titan and send text messages to the pilot with navigation instructions.

(Compiled by Jonathan Allen; editing by Jonathan Oatis)