Operation underway: Timeline of OceanGate's missing Titanic tour submarine and the mission to save its crew

OceanGate's Titan sub has less than 30 hours of oxygen remaining

News of OceanGate Expedition's missing submarine exploded on Monday as the U.S. and Canadian coast guards sprang into action with search and rescue missions.

Here is the timeline of how OceanGate's Titan submersible went missing during its descent to the wreckage of the Titanic.

JUNE 17

U.K. billionaire Hamish Harding, one of the tourists aboard the missing sub, posts to Facebook one day before the sub is set to begin its descent.

"Due to the worst winter in Newfoundland in 40 years, this mission is likely to be the first and only manned mission to the Titanic in 2023," Harding wrote "A weather window has just opened up and we are going to attempt a dive tomorrow. We started steaming from St. Johns, Newfoundland, Canada yesterday and are planning to start dive operations around 4 a.m. tomorrow morning. Until then we have a lot of preparations and briefings to do."

LIVE UPDATES: SEARCH FOR OCEANGATE’S TITAN SUBMARINE 

JUNE 18

Harding boards the submersible alongside Pakistani businessman Shahzada Dawood, 48, and his son Sulaiman Dawood, 19. OceanGate CEO Stockton Rush also boards the submersible, as well as an OceanGate pilot whose identity has not been confirmed.

Critically, the crew are sealed into the vehicle with 17 bolts, and it cannot be opened from the inside. The craft has enough stored oxygen to keep the crew alive for 96 hours.

The Titan then departs the Polar Prince mothership Sunday morning and begins its descent over the wreckage of the Titanic. The ship loses contact with the submersible 1 hour and 45 minutes into the dive.

This file image provided by OceanGate shows the Titan submersible being towed in Everett, Washington. (OceanGate Expeditions)

JUNE 19

At an unknown time, OceanGate sounds the alarm from the Polar Prince that the submersible has gone missing.

Immediately, the U.S. Coast Guard Northeast diverts a C-130 aircraft already in the area to begin searching the ocean surface. The Titan is designed to automatically surface in the event of a technical failure. If it is on the surface, rescuers must reach it within the 96-hour window to unseal the vehicle and release the crew.

Some failure may have caused the vehicle to remain stuck underwater. Rescue Coordination Center Halifax in Canada also delivers a P8-Poseidon aircraft, which is capable of dropping sonar buoys that can search underwater.

The U.S. and Canadian coast guards also dispatch more aircraft to the search area, located 900 miles off the U.S. northeast coast.

During this time, Harding's stepson, Brian Szasz, confirms that Harding is on board the submersible in a statement on social media.

This file image provided by OceanGate shows the Titan submersible descending into the ocean. (OceanGate Expeditions)

JUNE 20

Rescuers have been searching for roughly 48 hours and have covered 10,000 square miles of ocean, with no sign of the missing submersible.

Engro Corp. confirms that Dawood and his son are aboard the submersible in addition to Harding. OceanGate also confirms that CEO Rush is on board.

IMAGES SHOW OCEANGATE TITAN SUBMARINE'S FINAL MOMENT BEFORE IT BEGAN DIVE TO TITANIC 

"All that we know so far is that contact was lost with their submersible craft," Engro wrote at the time. "There is limited information available beyond this that we know, and we humbly request that speculation and theorization is avoided."

Meanwhile, rescue efforts are ongoing as the U.S. Coast Guard reaches out to both the U.S. Navy and the private sector for assistance. A commercial pipe-laying ship arrives to the area. Rescuers hope it will allow them to search depths of up to 3,800 meters after an unsuccessful night.

The U.S. Coast Guard delivers an update on their rescue efforts and say the Titan craft has 40-41 hours of oxygen remaining as of 1 p.m. ET.

Capt. Jamie Frederick, the response coordinator for the USCG's first district, explains that the Coast Guard does not have the equipment or expertise to conduct deep-sea search and rescue. The U.S., Canada and the private sector are working in concert to provide the necessary equipment and skill for such a search, such as remote-operated vehicles (ROVs) that can dive to the necessary depths.

Officials stressed that they are continuing to search for the submersible on the surface, however.

Assets now searching for the lost submersible include:

• Canadian CGS John Cabot
• Canadian CGS Ann Harvey
• Canadian CGS Terry Fox
• Canadian CGS Atlantic Merlin (ROV)
• Motor Vessel Horizon Arctic
• Commercial Vessel Skandi Vinland (ROV)
• French Research Vessel L’Atalante (ROV)
• His Majesty's Canadian Ship Glace Bay (mobile decompression chamber and medical personnel)

An undated photo shows tourist submersible belongs to OceanGate descents at a sea. Search and rescue operations continue by US Coast Guard in Boston after a tourist submarine bound for the Titanic's wreckage site went missing off the southeastern coast of Canada. (Ocean Gate / Handout/Anadolu Agency via Getty Images)

JUNE 21

The USCG announces that a Canadian P-3 aircraft had detected "underwater noises" in the search area.

As a result, available ROVs were diverted to the area to begin searching. They had found nothing as of 12:18 a.m., but still continued their search.

The Coast Guard says the noise data from the P-3 aircraft, which dropped sonar buoys in the area, has been delivered to the U.S. Navy for further analysis.

MISSING TITANIC SUBMARINE: CANADIAN UNDERWATER ROBOT SEARCHES OCEAN FLOOR AS OXYGEN LEVELS DWINDLE

JUNE 22

The USCG tweeted Thursday that the Canadian vessel Horizon Arctic has deployed a remotely operated vehicle (ROV) "that has reached the sea floor and began its search for the missing sub." 

It's the first time during the search that a vessel is combing the floor of the Atlantic Ocean for the Titan submarine. 

The Coast Guard also announced the French vessel L'Atalante has deployed their ROV. 

Weather conditions at the scene are 14 mph winds with gusts up to 19 mph. There are 4-5 ft. ocean swells and the air temp is 50 degrees Farenheit. 

The oxygen inside the submersible is estimated to run out sometime Thursday morning.