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On 21 December 1872, the British naval corvette HMS Challenger sailed from Portsmouth, England on an historic endeavor. Although the sophisticated steam-assisted sailing vessel had been originally constructed as a combat ship, her instruments of war had been recently removed to make room for laboratories, dredging equipment, and measuring apparatuses. She and her crew of 243 sailors and scientists set out on a long, meandering circumnavigation of the globe with orders to catalog the ocean’s depth, temperature, salinity, currents, and biology at hundreds of sites⁠—an oceanographic effort far more ambitious than any undertaken before it.

For three and a half long, dreary years the crew spent day after day dredging, measuring, and probing the oceans. Although the data they collected was scientifically indispensable, men were driven to madness by the tedium, and some sixty souls ultimately opted to jump ship rather than take yet another depth measurement or temperature reading. One day in 1875, however, as the crew were “sounding” an area near the Mariana Islands in the western Pacific, the sea swallowed an astonishing 4,575 fathoms (about five miles) of measuring line before the sounding weight reached the floor of the ocean. The bedraggled researchers had discovered an undersea valley which would come to be known as the Challenger Deep. Reaching 6.78 miles at its lowest point, it is now known to be the deepest location on the whole of the Earth. The region is of such immense depth that if Mount Everest were to be set on the sea floor at that location, the mighty mountain’s peak would still be under more than a mile of water.

Nothing was known of what organisms and formations might lurk at such depths. Many scientists of the day were convinced that such crevasses must be lifeless places considering the immense pressure, relative cold, total lack of sunlight, and presumed absence of oxygen. It would be almost a century before a handful of inventors and explorers finally resolved to go down there and take a look for themselves.

In the years that followed the Challenger expedition, subsequent surveys of the region ascertained that the Challenger Deep is part of a much larger formation, the massive Mariana Trench. This 1,580 mile-long trench is the result of the Pacific tectonic plate subducting beneath the Mariana Plate, and the water pressure at its floor is so difficult to comprehend that it is oft described with incomprehensible analogies as “the weight of fifty jumbo jets,” “the weight of 1,600 elephants on every centimeter of your body,” or “all life as you know it stopping instantaneously and every molecule in your body exploding at the speed of light.”

The first scientist with the know-how and wherewithal to seriously consider a dive to the bottom of the Mariana was Auguste Piccard, a Swiss professor, physicist, and inventor of some repute. In the early 1930s, he had gained considerable scientific fame by constructing and piloting the world’s first manned stratospheric balloon, using a pressurized sphere and helium gasbag of his own design to reach altitudes than no human had previously attained. From over 70,000 feet, he conducted experiments to measure cosmic rays, and made measurements to help prove the theories of his friend Albert Einstein. Piccard’s wife⁠—mortified that a middle-aged man would repeatedly subject himself to such risks⁠—insisted that he retire his ballooning career. Much to her surprise, he agreed.

It turned out that he had grander plans afoot. Piccard had realized that a variation of his stratospheric balloon concept could be used as a deep-sea diving apparatus, and he soon set to work constructing his first bathyscaphe vehicle. The contraption consisted of a high-pressure passenger sphere suspended beneath a different kind of gasbag⁠—a steel float chamber filled with gasoline. Gasoline is much lighter than water, causing it to be buoyant; yet it does not compress as air would, which allowed the tank to resist crushing even at extreme depths. The bathyscaphe operated a bit like an underwater zeppelin: operators descended by using pumps to replace small portions of gasoline with seawater, thereby reducing buoyancy. To ascend, operators used controls to let loose some of the onboard iron pellets used as ballast, thereby increasing buoyancy. Small electric propellers provided horizontal navigation.

Piccard finished his prototype in 1948, and conducted a number of unmanned test dives as far as 10,000 feet. In 1950 he sold the vehicle to the French Navy in order to begin construction on an improved design, the bathyscaphe Trieste. The new vehicle’s thirteen-metric-ton pressure sphere could accommodate two passengers⁠—albeit quite cramped⁠—and included oxygen tanks, rebreathers, and carbon dioxide scrubbers. Its hull was five inches thick, and it had a single, five-centimeter-wide window made from a thick cone of lucite⁠—the only transparent material capable of withstanding the depths this vehicle was intended to reach. After the craft had undertaken a number of successful test dives, the US Navy purchased the Trieste and shipped it to the Marianas to use it in Project Nekton⁠—a series of dives into the ocean’s deepest, darkest recesses to gather information regarding sunlight penetration, underwater visibility, transmission of man-made sounds, and marine geological studies of the trench.

On 23 January 1960, two men clambered aboard the Trieste for its attempt to dive into the Challenger Deep of the Mariana Trench: marine specialist Lieutenant Don Walsh of the US Navy; and oceanographer Jacques Piccard, son of the vehicle’s inventor. At 76 years of age, Auguste himself was unable to take part personally. The two hydronauts were expected to be confined in their battery-powered pressure sphere for over eight hours, including almost four hours each for the seven-mile descent and re-ascent. Since no manned or unmanned vessel had ever braved the journey to the Challenger Deep, no one was sure how much life, if any, would be found there. Most scientists were reasonably sure that microorganisms would be found, but some thought it unlikely that vertebrates could withstand such an inhospitable environment.

The men engaged the pumps to fill the ballast tanks with water, and the Trieste slipped beneath the waves to begin its long descent. It only took about sixteen minutes for the explorers to enter the aphotic zone⁠—the depth at which no light from the surface is present⁠—and the world outside the tiny window was left in utter darkness aside from the occasional faint flicker of phosphorescent organisms. From time to time the Trieste would slow and stop as she encountered a deeper, colder thermal layer, and more gasoline had to be pumped from the float chamber in order to continue the descent. The two men periodically reported their progress via a sonar-based phone handset, however there was little to report aside from the rapidly rising readings on the pressure gauges and the falling readings on the thermometers. The warmth inside the uninsulated sphere steadily dwindled.

Partway into their long descent, Walsh and Piccard grew alarmed when they discovered they were no longer able to raise the mother ship on the sonar/hydrophone communication system, even after repeated attempts. The two men were thus left truly isolated from the outside world. Curled up in the cramped, cold, and dimly-lit sphere, the adventurers continued their hours-long downward journey with only one another’s voices and the occasional pop or groan from the Trieste’s strained hull to punctuate the anxious silence.

At approximately four hours into their descent⁠—several thousand feet above the sea floor⁠—a sharp clang sounded through the pressure sphere and the vehicle shuddered violently. Once their wincing subsided, the men did what they could to inspect the craft and its condition. It seemed that the water pressure at this never-before-encountered depth⁠—six tons per square inch⁠—had cracked the outer pane of the lucite window. For the moment the vehicle itself remained watertight, but the damage was worrisome. The Trieste was outfitted with a few safety systems; for instance, the ballast doors were held closed by electromagnets, so in the event of electrical failure the doors would fall open and drop the ballast, causing the vehicle to rise to the surface. But such systems would be of no help to the men inside if the 1,000 atmospheres of pressure crushed their delicate passenger compartment. Moreover, no other vehicle in existence was capable of reaching such depths, which meant that if her float tank became compromised there was no chance of rescue. Nevertheless, the stalwart scientists opted to press on.

About three quarters of an hour later, the bathyscaphe Trieste made history as its hull came to a gentle rest on the silty floor of the Challenger Deep abyss. The Trieste and her crew had spent four hours and forty-eight minutes in transit. The bathyscaphe instrumentation indicated a depth of 37,798 feet and external pressure of 1,099 atmospheres⁠—approximately eight tons per square inch. The scientists flicked on the exterior lights to cast light on a patch of earth that had not been illuminated in millions of years, and peered out through the peephole. Through the swirling clouds of agitated silt and sediment the pair could make out a flatfish which had been disturbed by the vehicle’s unexpected touchdown. They also spotted some shrimp and jellyfish swimming nearby. These observations proved that the water even at such depths was not stagnant and stationary⁠—there was sufficient ocean current to bring in oxygen for complex life. The mission was not equipped with cameras, however, so the historic exploratory moment was sadly left unphotographed.

Walsh and Piccard attempted to use the sonar/hydrophone handset again, and found that it had inexplicably regained function. They reported their arrival and observations to the mother ship, and although their voices took approximately seven seconds to cross the seven miles of water, they came through quiet yet clear. The hydronauts observed the “diatomaceous ooze” through their tiny, cracked window, shivering in the 45F degree cold and munching chocolate bars to regain lost calories. For the most part, the few organisms they observed were little different from those found in the miles of water above them. Thirty or so minutes later, concerned that the damaged lucite porthole would not withstand the pressure indefinitely, the men dumped two tons of iron ballast and the vehicle slowly began to rise. Three and a quarter uneventful hours later, the bathyscaphe Trieste bobbed to the Pacific surface, having entered the history books with a record that could never be bested. Walsh and Piccard had been to the abyss and back.

Later the same day, the US Department of Navy issued a press release boasting that “the United States now possesses the capability for manned exploration of the sea down to the deepest part of its floor.” Project Nekton was a success. Jacques Piccard and Lt. Don Walsh were flown to Washington DC to receive decorations from President Eisenhower, and to retell the story of their descent of alternating boredom and terror.

Grand plans were hatched to do further research with the intrepid bathyscaphe, including bringing back samples of water, soil, and organisms from the abyssal trench. The US Navy, however, was less enthusiastic. The millions of dollars they had invested in the mission had not borne any particularly compelling scientific fruit aside from proving that such a dive was possible. Perhaps most importantly, they had demonstrated America’s deep-sea dominance to the pesky Soviets. Moreover, the public’s fickle attention was fixed rather firmly on the developing Space Race, leaving little interest in oceanic exploration.

For a few years the Trieste continued her career as a diving vehicle, though never again to such depths as the Challenger Deep. Most of her later missions were pedestrian by comparison, although when the nuclear submarine USS Thresher was lost at sea in 1963 she did participate substantially in the search efforts. Soon thereafter she was retired, and many of her systems were incorporated into other dive vehicles. Much of her outer hull was left intact, however, and it is currently on exhibit at the Navy Museum in Washington, DC. In the 45 years since the Trieste was taken out of service, there has not been another manned dive vehicle capable of reaching the floor of the Mariana.

Even today, less than 5% of the Earth’s oceans have been explored by humans according to the US National Oceanic and Atmosphere Administration. Of course humanity has not entirely abandoned the exploration of the deep. In 1995 a robotic probe did finally revisit the faraway floor of the Mariana trench, as did another such probe in 2009. Though we must not diminish the achievements of those plucky remote-controlled explorers, it seems a shame that no humans have ever attempted to return. There are some people who say that there is little value in sending humans to harsh places where hardier robotic proxies can go in their stead; but for the indefatigable adventurer, that sort of stick-in-the-mud, stay-at-home complacency is unfathomable.

Update 25 March 2012: Famed Hollywood director James Cameron has since become the third human to visit Earth’s deepest chasm. He’s like the Pete Conrad of the Mariana.

Update 13 May 2019: A third expedition has reached the floor of the Mariana. Victor Vescovo found human garbage in the ocean’s deepest trench.

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