Unless you’ve been living under a rock, you’ve probably heard of the cruise ship Titanic that sank after striking an iceberg in the early 1900s. There’s even an iconic romance movie based on the shipwreck. Earlier this week, it was reported that a tourist submarine that’d taken guests on an expedition to see the underwater wreckage of the Titanic had gone missing. The vessel had five people on board, including a British billionaire. What Exactly Happened? In the morning of June 18, a tourist submarine, named the Titan, submerged on a dive in the Northern Atlantic Ocean. Its five-person crew, including one pilot, was bound for the Titanic wreckage site. The submarine was owned by OceanGate Expeditions, a company specialising in deep-sea exploration. Just an hour and 45 minutes later, staff on the ship, the Polar Prince, lost contact with the submarine. At that time, the submarine was lost in an area around 1,448 km from Cape Cod, near the United States. It was at a depth of around 13,000 feet underwater—for reference, the tallest building in the world stands at a height of 2,717 feet. What Kind Of Submarine Is This? The missing vessel is called the Titan, a 6.5 m long submersible capable of carrying a crew of five. According to OceanGate’s website, the sub is able to submerge to a depth of 4,000 metres, or 13,123 feet. It’s also equipped with a real-time health monitoring system to track the conditions of the dive and account for factors like shifting pressure, structural integrity and strain. This allows the pilot to assess the conditions of the dive and detect anomalies in real time. Passengers inside the submarine are unable to exit the sub unless assisted by a crew member outside—even if it were possible to escape the sub at that depth, though, they’d be crushed by the pressure. To get to the Titanic wreckage site, the sub would have to travel for around 2 hours, to a depth of 3,800 metres. Who Is Missing? These expeditions are expensive, so the passengers are usually wealthy people—their dive on the Titan cost US$250,000 per person (around SGD 335,971). The passengers on board the craft comprised one pilot and four other pretty high-profile individuals, including British billionaire Hamish Harding. The 58-year-old, who founded an aviation company, is a known thrill seeker—just a year ago, he went to space as a space tourist (yes, that exists now). He’s no stranger to deep-sea dives as well, and he even holds a Guinness world record for longest duration and distance traversed at full ocean depth by a crewed vessel. The other missing people include a 48-year-old Pakistani businessman, Shahzada Dawood, and his 19-year-old son Suleman. The pilot, Mr Stockton Rush, was originally a jet transport pilot turned deep-sea vessel pilot. He currently serves as the chief executive of the company behind the dive, OceanGate Expeditions. He was accompanied on the dive by a 77-year-old French submarine operator nicknamed Mr Titanic, Paul-Henri Nargeolet, who conducted extensive research into the Titanic’s crash and concluded a different main cause. Mr Nargeolet had visited the Titanic’s wreckage more than 30 times before this. Rescue Operations Underway Today (Wednesday) marks the fourth day of the search, after the submarine went missing Sunday morning. The rescuers include teams deployed by Canadian and American authorities. The US Coast Guard is currently cooperating with the US Navy and Canadian Coast guard in the search. Aircrafts and other underwater vessels equipped with deep-sea searching technology have also been deployed to aid in locating the missing sub. Other vessels, including privately-owned crafts, have also been deployed and are en-route to provide assistance. However, the search remains difficult—the area the sub was lost in is remote, and it’s deep underwater. Authorities are also pressed for time. As of today, the submarine only has around 24 hours of oxygen left, making rescue operations extremely urgent. Recovering the sub, if it’s found, is no easy feat as well. Only a few assets are equipped to travel that deep—the US military has deployed remote-operated vessels to find it. These vessels, however, are unable to lift the sub to the surface. Although efforts are focused on the search, authorities are also working on a rescue plan if the sub is found. How Did It Go Missing? According to CBS correspondent David Pouge, who had previously accompanied the Titan’s crew to the Titanic’s wreckage site, the Titan does not have a GPS. Because there aren’t any GPSes underwater, the Titan’s expedition is guided by the crew on the surface ship, who send the pilot text messages providing directions to the shipwreck. However, communications with the surface ship were lost during this dive—it’s possible an antenna used for communications might’ve become dislodged or broken. The pressure is also incredibly high at that depth—doors and windows of the craft cannot physically be opened, and the human body cannot withstand the pressure outside the vessel. Banging Noises Heard Days into the gruelling search, a Canadian aircraft picked up “banging noises” in the area of the vessel’s last known location. According to the search crew, their sonar devices picked up banging noises in thirty-minute intervals this Tuesday (20 June). The aircraft, a P8 Poseidon, is equipped with technology facilitating underwater detection from the air. The sonobuoys it deployed picked up these “banging noises” every thirty minutes. Four hours later, when additional sonobuoys were deployed, the noises could still be heard. The vessel is equipped with a 96-hour supply of emergency oxygen—since it went missing Sunday morning, the passengers only have around 24 hours of oxygen left. Since it’s designed for short-term travel, the sub does not have seats, and passengers sit on the floor. It only has one toilet. How Dangerous Was It? According to G. Micheal Harris, founder of a company specialising in Titanic retrieval expeditions, dives to the wreckage usually happen in a three-month window when conditions are calmer. This period is usually between the end of June to September—the Titan’s dive happened early in the season. Mr Harris said that the Titan probably was not equipped with a transponder system, which would allow for constant communication with the surface ship. On Mr Pogue’s voyage with the Titan, the vessel had wound up lost for a few hours. The company has also faced a lawsuit regarding the safety of their vessels. As of Wednesday evening, the search continues.