The Voyage of the “Trieste”

In January 1960, two ocean explorers named Don Walsh and Jacques Piccard took the manned submersible Trieste to the bottom of the Challenger Deep in the Marianas Trench, the deepest spot in the ocean. It was a feat that would not be duplicated for another half-century.

Bathyscaphe_Trieste_hoisted

The Trieste is lowered into the water.                            Photo by US Navy

In 1872, the Royal Society of London set out to make the first systematic scientific study of the ocean floor, planning a series of soundings to measure the water depths and using bottom dredges to examine ocean sediments and sea floor life. The British government provided the Royal Navy vessel HMS Challenger, who had her guns removed and replaced with scientific equipment. In December 1872, Challenger left on an around-the-world voyage. Over the next three years, she sailed over 70,000 miles. At 360 pre-selected points, the ship stopped to take scientific readings: weighted ropes were used to measure the ocean depth, collection jars were used to scoop up bottom sediments and water samples, trawling nets were used to capture fish and dredges were used to collect sea floor life for study, and instruments were used to measure salinity and temperature at various depths. It was the most comprehensive study of the oceans ever undertaken.

On March 23, 1875, at Station Number 225, near the Pacific island of Guam, the Challengermeasured the greatest depth it encountered, an incredible 4,475 fathoms (26,850 feet, or about five miles). This spot became known as the “Challenger Deep”, and it remains the deepest part of the ocean ever found. Subsequent investigation by British, American and Soviet research vessels using sonar determined that the Challenger Deep was actually part of a long underwater canyon, known as the Marianas Trench, that drops to depths of 36,000 feet, or almost 7 miles–deeper than Mt Everest is tall. (Today, we know that the Marianas Trench is a subduction zone, where one of the Earth’s tectonic plates are being pushed underneath another.)

In the 1930’s, it finally became technically possible for humans to descend to great depths in the ocean. The fish biologist William Beebe used a bathysphere, a steel sphere with quartz windows that was lowered by cable from a ship, to descend up to 3,000 feet off the coast of Bermuda in a series of dives sponsored by the New York Zoological Society and the National Geographic Society. In the 1940’s, Swiss explorer Auguste Piccard, who had already set several altitude records in his self-designed pressurized hot-air balloon gondola, modified the basic bathysphere to produce a free-moving version called a bathyscaphe. Rather than being lowered and raised on a steel cable, the bathyscaphe’s steel sphere used a large separate flotation tank filled with gasoline and ballast made from iron pellets. The heavy ballast pulled the manned sphere down into the ocean, and when the iron pellets were dumped, the lighter-than-water gasoline pulled the bathyscaphe back to the surface. Small propellers and rudders allowed the craft to be maneuvered underwater. Piccard’s son, Jacques, piloted the craft. The first bathyscaphe, called FNRS-2, was operated by the French Navy, and reached depths up to 13,701 feet.

Piccard’s next bathyscaphe design was built in Italy and named Trieste. She measured 59 feet 6 inches long, 11 feet 6 inches wide, and 18 feet 6 inches tall. As flotation, Trieste carried 22,000 gallons of gasoline, and 9 tons of iron pellets for ballast. The crew compartment was a 7-foot sphere with walls five inches thick, with a single Plexiglas window. Two electric propellers allowed the submersible to maneuver, electric batteries provided the power, and air tanks provided oxygen to the crew (the carbon dioxide was removed with chemical scrubbers). Triestecould carry two people. She made her first dive in the Mediterranean, for the French Navy, in 1953.

In 1958, a marine biologist named Robert Deitz proposed to the US Navy that they construct a bathyscaphe to provide access for studying deep-sea marine life, and the Navy, interested in the possible military applications of the technology, agreed to fund “Project Nekton”. Rather than design and build their own bathyscaphe, however, the Navy instead purchased the Trieste from France, for $250,000. Jacques Piccard came with the submersible to train an American pilot, and US Navy Lieutenant Don Walsh was assigned that task. During 1959, a series of seven progressively-deeper dives, eventually reaching 24,000 feet, were made off the coast of Guam into the Marianas Trench.

On January 23, 1960, Piccard and Walsh entered Trieste for another dive–and this time the target was the bottom of the Challenger Deep, the deepest spot in the ocean. At daybreak, as the submersible was lowered into the water, rough seas pounded them, and the waves damaged the telephone line still connected to the mother ship (the USS Wandank), and also knocked out some of the instruments, but it was decided to go ahead with the dive anyway. At 8:23 am, theTrieste dropped below the surface and began her voyage to the sea floor. The heavy iron ballast pulled the entire submersible down at a rate of one meter per second.

At a depth of 300 feet, just ten minutes into the dive, the Trieste encountered a problem. There was an unusually cold layer of water here, and it was too dense to allow the submersible to sink through it until the gasoline in the float tank cooled to the same temperature. Rather than waste the valuable dive time, Piccard and Walsh decided to release some of their gasoline, loweringTrieste’s buoyancy and allowing the descent to continue. This was repeated three more times, until finally at 530 feet the gasoline cooled enough for an uninterrupted descent. As they went deeper, the air temperature inside the sphere began to drop, reaching 42 degrees, and forcing the crew to put on dry suits. During this time, they were also able to communicate with theWandank on the surface using an underwater radio hydrophone.

At 11:30 am, at a depth of about 30,000 feet, Piccard and Walsh turned on the sonar system that would detect the seafloor below them. Shortly after that, at a depth of 32,000 feet, they were startled to hear a loud popping sound that shook the entire sphere. Although they stopped their descent and examined all their instruments, they could not see anything wrong.

The Trieste continued its descent and, at 2:06 pm, it settled on the bottom of the Challenger Deep. The onboard depth gauges read 37,799 feet, though this was later corrected to 35,814 feet. The descent had taken 4 hours and 48 minutes.

They had enough air supply to spend about 30 minutes on the bottom. Looking out the window, they almost immediately saw a fish–a sole about one foot long–swimming away from them, and noticed that the ocean floor here was a smooth milky-white sediment layer of diatomaceous ooze. A few shrimp also paddled past the window. To their mild surprise, they found that the underwater hydrophone was still able to make contact with the surface ship, though the radio signal took seven seconds to travel each way. In the time remaining, Walsh and Piccard took external water temperature readings (38 degrees), checked for any water currents at this depth (there were none), and measured the radiation levels of the sea floor (there was no measurable radiation).

When they turned on the rear searchlight, which shined light directly onto the window, Piccard and Walsh learned what had caused that popping sound they had heard on the way down–the outer panel of the multi-layered Plexiglas window had cracked under the enormous water pressure. Fortunately, the inner layers held. If the window had given way, the surrounding sea water would have crushed them both instantly. But now they decided to cut the mission short and leave the bottom after just 20 minutes. The iron pellet ballast was dumped onto the sea floor, and the big gasoline-filled flotation bag now acted like a balloon to pull the Triesteupwards. The ascent took 3 hours and 15 minutes.

It was another 35 years before the Challenger Deep was again explored and filmed. In 1995, 1996 and 1998, the unmanned Japanese tethered probe Kaiko reached depths up to 35,755 feet. Then in 2009 the US Navy’s free-swimming remotely-piloted vehicle Nereus reached depths up to 35,768 feet and spent ten hours at the bottom. But after the Trieste there were no other manned descents into the Challenger Deep until March 2012, when film director James Cameron piloted the Deepsea Challenger and spent two and a half hours on the bottom at a depth of 35,756 feet.

After her dive in 1960, the Trieste underwent some modifications, then was used in 1963 to help locate the wreckage of the sunken nuclear submarine USS Thresher in the Atlantic. A year later, the Trieste was dismantled, and her pressure sphere was incorporated into her successor, the bathyscaphe Trieste II. The Trieste II served with the Navy until 1980. She is now on display at the Naval Undersea Museum in Keyport, Washington.

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