“At Bottom. Repeat. At Bottom.”

Multimillionaire Victor Vescovo committed himself to one of the world’s craziest remaining adventure quests: to reach the deepest points in every ocean, in a dangerous mission called the Five Deeps. What does it take to get there? A radically high-tech, $30 million Triton submersible, a team of crack engineers and scientists, and one very gonzo explorer.

- Susan Casey

IT WAS A SUNDAY IN TONGA, so the kingdom’s business had come to a halt. Stores were shuttered, traffic was quiet, even the airport was closed. King Tupou VI strolled out of his oceanfront palace and down the main street of Nukualofa, capital city of the island of Tongatapu, to attend church along with the rest of his South Pacific nation. Men wore their best sarongs; women wore taovalas—coconut-fiber aprons—over long dresses. The scene was all very ordinary except for one thing, and it was visible from the palace’s front lawn: a 224-foot ship moored at the pier, bristling with heavy cranes, stacked with high-tech equipment, and carrying a mysterious $30 million cargo.

“Welcome to the good ship Pressure Drop,” said Rob McCallum, who stood on deck in khaki shorts, river shoes, and a polo shirt emblazoned with the emblem of the Five Deeps Expedition, a black shield bearing the Latin phrase IN PROFUNDO: COGNITIO (“In the Deep: Knowledge”). A former New Zealand national park ranger who grew up in Papua New Guinea, 54-year-old McCallum is a legendary expedition leader. He specializes in bespoke trips to far-flung places, some of which happen to be underwater, like the wreck of the Titanic. Five Deeps, however, was something even more extreme: a global mission to dive a manned submersible to the deepest point in the Atlantic, Pacific, Indian, Arctic, and Southern Oceans. This had never been done before— which is exactly why McCallum’s client, Texas businessman Victor Vescovo, had set out to do it.