A day before the disappearance of the doomed Titan submersible, a British businessman and explorer wrote of his pride to be "going down to the Titanic" as a mission specialist.
Hamish Harding said via social media Saturday that "a weather window has just opened up" after "the worst winter in Newfoundland in 40 years." A veteran of extreme expeditions, Harding said he would be accompanied by "a couple of legendary explorers" on the dive starting early Sunday morning.
His last social media post included a photo of the OceanGate submersible and another of Harding signing a Titanic Expedition banner.
The dive "is likely to be the first and only manned mission to the Titanic in 2023" because of the particularly harsh winter, Harding wrote last Saturday -- one day after the expedition departed from St. John's, Newfoundland, Canada, on the mother ship Polar Prince.
The next day, the submersible suffered a "catastrophic implosion," killing all five people on board, US Coast Guard Rear Adm. John Mauger announced Thursday, four days after the craft vanished in the vicinity of the 111-year-old wreckage of the Titanic in the depths of the North Atlantic. The announcement ended a desperate international search and rescue effort that captured global attention.
In addition to Harding, the other passengers on board were Stockton Rush, the OceanGate CEO and founder; Pakistani billionaire Shahzada Dawood and his son Suleman Dawood; and French diver Paul-Henri Nargeolet, a renowned Titanic expert with decades of exploring experience.
These were the unsettling days since the Titanic submersible's demise:
Sunday, June 18: 'Discover something truly extraordinary'
At the site of the Titanic wreck, roughly 900 miles off the coast of Cape Cod, Massachusetts, the submersible began its two-hour-long descent of 12,500 feet below sea level. The $250,000 per person expedition was billed as "a chance to step outside of everyday life and discover something truly extraordinary," according to an archived version of OceanGate's website.
It was 9 a.m. Atlantic Daylight Time (one-and-a-half hours ahead of Eastern Time), according to Miawpukek Maritime Horizon Services, which co-owns the Polar Prince.
At 11:47 a.m., the 21-foot submersible lost contact with its mother ship. With no GPS underwater, the craft was only guided by text messages from the surface ship.
Hours later, at 6:10 p.m., the submersible failed to resurface as scheduled. Authorities were notified at 6:35 p.m., according to Miawpukek Maritime Horizon Services, launching an international search and rescue effort.
Monday, June 19: A race against time
The Titan has four days of emergency capability, Mauger told reporters.
The sub's 96-hour emergency air supply set up Thursday morning as a crucial search target.
US and Canadian coast guard crews scoured the ocean's surface and used sonar to listen for sounds far below the water. Commercial ships also assisted in the search.
On Facebook, Rory Golden, an expedition participant on board the Polar Prince, urged people to "think positive. We are."
OceanGate Expeditions said in a statement Monday night it was taking "every step possible" to return the five crew members.
Tuesday, June 20: An 'Interminable wait' and dwindling oxygen supply
Sonar picked up banging sounds from underneath the water in the North Atlantic Ocean while searching for the submersible, according to an internal US government memo on the search.
Crews detected banging sounds every 30 minutes -- and hours later, after additional sonar devices were deployed, banging was still heard, according to the memo obtained by CNN. It was unclear when the banging was heard or for how long.
The underwater noises were detected by a Canadian P-3 aircraft, prompting the relocation of resources to explore their origin, the US Coast Guard said via Twitter, adding that the "searches have yielded negative results." US Naval experts were analyzing the data.
On Tuesday afternoon, US Coast Guard Capt. Jamie Frederick estimated the vessel was down to 40 hours of oxygen. Officials were unsure whether that was enough time to rescue those onboard.
With the arrival of new equipment, searchers had taken the operation below sea level after scouring an area of the ocean's surface about the size of Connecticut, according to Mauger.
"What we're going through right now is this interminable wait," Mathieu Johann, a friend of Nargeolet, told CNN.
Wednesday, June 21: A 'search-and-rescue mission, 100%'
Canadian P-3 aircraft detected underwater noises in the search area, according to the US Coast Guard.
Underwater remotely operated vehicles were relocated to explore the origin of the noises, and data was sent to US Navy experts for analysis.
It was unclear whether the noises heard Tuesday night and Wednesday morning were from the missing submersible, according to Frederick.
"I can't tell you what the noises are," Frederick said, but he stressed that the operation was still a "search-and-rescue mission, 100%."
If the craft is in the deep ocean, staying warm and lucid will be the biggest hurdles for the five passengers, experts warned.
"They're freezing cold," retired Navy Capt. David Marquet told CNN. "They're all huddled together trying to conserve their body heat. They're running low on oxygen and they're exhaling carbon dioxide."
The US moved in military and commercial assets as aircraft from the Canadian Armed Forces, the US Coast Guard and the New York Air National Guard looked above and below the water. A research ship with an underwater robot was dispatched by France to join the mission.
The banging noises provided faint hope in a dire situation made worse by emerging reports about OceanGate's operations and safety practices.
Thursday, June 22: 'A light switch was switched off'
Minutes before a US Coast Guard news conference Thursday afternoon, OceanGate Expeditions issued a statement grieving the five men on board.
"We now believe that our CEO Stockton Rush, Shahzada Dawood and his son Suleman Dawood, Hamish Harding, and Paul-Henri Nargeolet, have sadly been lost," OceanGate said in a statement.
"These men were true explorers who shared a distinct spirit of adventure, and a deep passion for exploring and protecting the world's oceans. Our hearts are with these five souls and every member of their families during this tragic time. We grieve the loss of life and joy they brought to everyone they knew."
Mauger told reporters the submersible suffered a "catastrophic implosion."
The tail cone and other debris from the missing submersible were found by a remotely operated vehicle about 1,600 feet from the bow of the Titanic.
"This is an incredibly unforgiving environment down there on the sea floor and the debris is consistent with a catastrophic implosion of the vessel," Mauger said.
The families were immediately notified.
Five different major pieces of debris from the submersible were found in the area Thursday morning, officials said. Each end of the pressure hull was found in a different place, according to Paul Hankins, US Navy director of Salvage Operations and Ocean Engineering.
The US Navy said it detected an acoustic signature consistent with an implosion on Sunday in the general area where the submersible was diving when it lost communication, a senior Navy official told CNN.
The Navy then immediately relayed the information to the commanders leading the search effort, and it was used to narrow down the area of the search, the official said.
Still, the sound of the implosion was determined to be "not definitive," the official said, and the multinational efforts to find the submersible continued as a search and rescue operation.
"Any chance of saving a life is worth continuing the mission," the official said.
The US Navy also helped analyze the audio signatures of banging and other acoustic data that were heard during the search efforts, the Navy official said. Those were likely some form of natural life or sounds given off by other ships and vessels, according to the official.
It's unclear where or how deep the Titan was when the implosion occurred.
A catastrophic implosion is "incredibly quick," taking place within just a fraction of a millisecond, said Aileen Maria Marty, a former Naval officer and professor at Florida International University.
"Ultimately, among the many ways in which we can pass, that's painless," she said.
Tom Dettweiler, an ocean explorer and friend of Nargeolet, on Thursday recalled an expert's description of a catastrophic implosion in an Israeli submarine in 1968.
"For the crew, it was just like a light switch was switched off," he remembered the expert saying. "They didn't even realize what was happening. They didn't suffer."