CHALLENGER DEEP, MARIANA TRENCH, SOUTHEAST OF GUAM (WHTM) — The first dive to the deepest part of Earth’s oceans had its start with a record-breaking ascent into Earth’s atmosphere.

On May 27, 1931, Swiss physicist and inventor Auguste Antoine Piccard (1884-1962) climbed into a pressurized gondola he designed, and with fellow scientist Paul Kipfer took off from Augsburg, Germany, suspended from a hydrogen balloon (which Piccard also designed.) They became the first human beings to enter the stratosphere, reaching a height of 15,781 meters or, if you will, 9.8 miles or, if you will, 51,775 feet. That’s 22,743 feet higher than the summit of Mount Everest.

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The trip wasn’t just about setting an altitude record, though. Piccard and Kipfer gathered information about conditions in the upper atmosphere, as well as cosmic rays. Piccard’s pressurized gondola proved it was possible (with proper engineering) for human beings to survive at great heights. (Think about him the next time you’re breathing comfortably in an airliner at 35,000 feet.)

Piccard’s balloon design was just as important. He knew the hydrogen gas would expand as atmospheric pressure decreased. So, he made the balloon’s gas envelope flight larger than the amount of gas needed to get his gondola off the ground. The hydrogen could then expand without straining the bag. The same principle is used for balloons to this day-and Piccard’s understanding of the effects of pressure would prove essential when he turned his attention to exploring the sea.

Human beings had been exploring and working underwater for centuries, using various kinds of diving bells. But diving bells tend to sit (or dangle) in one place. Piccard wanted something that could move, and dive deep. In 1937 he designed the bathyscaphe, a sort of underwater blimp or dirigible.

Title: U.S. Navy Bathyscaphe Trieste General arrangement drawing, showing the bathyscaphe’s main features. Drawing was released in connection with Trieste’s record dive to 35,800 feet in the Challenger Deep, off Guam, on 23 January 1960. (U.S. Naval History and Heritage Command Photograph.)

Like an airship, the passenger gondola hangs under a floatation envelope. Unlike the gondola of Piccard’s balloon, however, the sphere on a bathyscaphe must resist pressure from the outside and has to be stronger. Much stronger. (I’ll toss out some numbers later on.)

Those pressures also meant Piccard couldn’t use any sort of gas for buoyancy. Ocean pressures are measured in “atmospheres.” Every 10 meters (or 33 feet) the pressure increases by one atmosphere-and gas compresses, becoming less buoyant. Instead of an envelope that would expand and contract with the lifting material, he needed a lifting material that wouldn’t expand and contract, to go in an envelope that wouldn’t need to expand and contract. (And it would help if the lifting material was cheap and readily available.)

Piccard’s solution-use liquid instead of gas for buoyancy. Liquids don’t compress as readily under pressure as gases, and some liquids are lighter than water. So Piccard filled the buoyancy chambers of his bathyscaphe with gasoline, a full 30% lighter than water. The bathyscaphe would float until water filled two ballast tanks, then start sinking slowly. To return to the surface, the operators would release iron ballast.

Piccard had to wait until after World War 2 to build his first Bathyscaphe, the FNRS-2. After a series of successful test dives, it was purchased by the French navy, extensively modified, and renamed FNRS-3. Auguste Piccard, now aided by his son Jacques, took what he had learned to design and build a third bathyscaphe, the Trieste, named after the city where it was constructed. It was launched in August of 1953, and over the next few years conducted a series of dives in the Mediterranean Sea.

The U.S. Navy purchased the Trieste in 1958. They planned to use it for Project Nekton, a series of research dives near Guam, and especially the Marianas Trench. The Navy modified Trieste for the project, equipping it with a new, stronger pressure sphere, manufactured by the Krupp company in Germany.

On October 5, 1959, Trieste left San Diego for Guam aboard a freighter. Guam had a major naval facility and was located only about two hundred miles from the Challenger Deep.

Over the next several months, Trieste performed eight dives, going progressively deeper. The first two dives were in Apra Harbor to test the bathyscaphe and its equipment. Dive three took her to a depth of 4,900 feet.

Dive four was the first really deep dive, to a part of the Marianas Trench known as the Nero Deep. Trieste reached a depth of 18,150 feet. As the ship returned to the surface, though, there was a loud bang at about 30 feet deep. Some epoxy seals had broken on the sphere, and some water leaked in. Trieste had to be hauled out of the water for resealing and adding reinforcing bands.

Dive five was another harbor test of the seals and some newly installed equipment. This was followed by a checkout dive to 5700 feet.

The seventh dive took Trieste to the Nero Deep of the Marianas Trench, a new record depth of 24,000 feet, and a couple of noisy, disconcerting explosions at around 20,000 feet. Somebody had forgotten to remove a portable navigation light, and a new pipe stanchion collapsed because no one had drilled holes in it to allow pressure to equalize. But there was no damage to Trieste herself, and it was time for the deepest dive of the series.

On January 23, 1960, Trieste slipped under the waves, beginning the five-hour-long trip to the Challenger Deep, located on the southern end of the Marianas Trench. On board were Jacques Piccard and Lt. Don Walsh. They took readings of temperature pressure, and descent speed, checked the ship’s systems, and peered out the tiny plexiglass window looking for signs of life, of which they saw very little besides phosphorescent plankton. They were able to communicate with surface vessels using a sonar telephone.

Then at 32,500 feet, something broke.

The pressure sphere shook and the men heard a cracking noise. But there was no obvious damage or leakage and the descent was continuing normally, so they pressed on.

And when they reached a depth of 35,797 feet, the Trieste quietly settled on the bottom of the Challenger Deep. One of the very first things they saw in their floodlight-a foot-long fish, swimming slowly away from the mysterious bright-eyed intruder. The question of whether life could survive at such crushing depths was answered. (“Crushing” is the right term; at 35,797 feet, water was pushing on the sphere at 15,519 pounds-over seven tons-per square inch.)

Walsh and Piccard spent twenty minutes on the bottom, taking measurements and peering out their viewport. At one point they swung their searchlight around and found out what had caused the shaking and noise. One of the plexiglass panels on their entrance tunnel had cracked. This wasn’t really a danger to the Trieste, but if it shattered on the way up, it would have to be replaced before they could clear the passageway and climb out of the sphere.

Fortunately, nothing else went wrong with the panel during the three-hour trip back to the surface-but they pumped out the passageway very slowly and carefully when they got to the surface.

The Challenger Deep would not be visited by a manned submersible for another 52 years. Finally, in March 2012, filmmaker and inventor James Cameron piloted a one-man submersible, the Deepsea Challenger, to the bottom, reaching 35,787 feet, and was able to spend several hours collecting samples and shooting video. (Don Walsh was an advisor on the project. )

Then on April 28, 2019, the DSV Limiting Factor reached a depth of 35,853 feet, beating Trieste’s record by 56 feet. It also became the first sub to make more than one dive-four in all between April 28 and May 5.

In 2020 the Chinese submarine Fendouzhe (“Striver”) completed 13 dives in the Marianas trench.

As for Trieste herself, you can see her at the Naval Museum in Washington, D.C. In 2020, Don Walsh was interviewed at the museum. You can see the interview here.

For footage of initial tests of the Trieste, click here.

For footage of one of Auguste Piccard’s balloon launches, click here.

So, Trieste’s record has been broken, after fifty-nine years, and more expeditions to the deepest point in the ocean may be expected. But Jacques Piccard, Don Walsh, and Trieste will forever be the first.