The Ocean Trenches No One Has Ever Reached

In the summer of 2024, China's crewed submersible Fendouzhe dropped into the Aleutian Trench in U.S. waters and mapped a whole ecosystem. It stopped about half a mile (a kilometer) short of the floor. Sonar has charted the deepest points of five other major trenches too. No crewed submersible has ever reached the floor of any of them. The reason is mostly supply. Just two crewed submersibles on Earth are rated to survive full ocean depth, each one costing around $37 million and built to shrug off 16,000 pounds per square inch. With that little capacity to go around, expeditions burn their dives on famous targets like Challenger Deep first. These six trenches are still waiting.

Manila Trench

At 17,717 feet (5,400 meters), the Manila Trench is the shallowest on this list, and the most feared. A 2006 U.S. Geological Survey workshop named it the single most dangerous earthquake source in the South China Sea, one capable of a Tohoku-scale rupture. West of Luzon and Mindoro, the South China Sea's oceanic lithosphere, part of the Eurasian Plate, grinds beneath the Philippine Mobile Belt, and it has not let go with a major quake since the 1560s.

That is the problem. Manila's 11 million-plus residents sit above it, and southern China, Taiwan, and Vietnam all fall within tsunami range. So the research goes into fault maps and rupture models. No documented expedition has reached the floor.

Vityaz Trench

Northeast of Vanuatu, the Vityaz Trench bottoms out at 20,013 feet (6,100 meters). Soviet oceanographers found it in 1958 aboard the research vessel Vityaz and named it for the ship. Then it did something no other trench here does. It died. A 1996 study in Marine Geophysical Research classified the Vityaz Trench Lineament as seismically inactive, a fossil subduction zone where ancient Cretaceous Pacific crust to the north meets younger Cenozoic basin floor to the south.

A 2020 survey found the floor flat and wide, more trough than classic V, and steeper on its eastern wall. The deep spots cluster in two bands, roughly 11,500 to 12,100 feet (3,500 to 3,700 meters) and 15,700 to 16,400 feet (4,800 to 5,000 meters), both well short of that 20,013-foot maximum. The neighboring Vanuatu Trench, for contrast, cuts nearly 23,000 feet (7,000 meters) deep with the sharp V you would expect. Sonar has mapped every foot of the Vityaz. No crewed submersible has been sent down.

Middle America Trench

In January 2022, Victor Vescovo's Caladan Oceanic put the Middle America Trench on its list of planned dives. The team had just made the first crewed descent into the neighboring Atacama Trench off Chile, so the ambition was real. Three years on, the Middle America dive is still pending.

The trench runs 1,678 miles (2,700 kilometers) along the Pacific coast of Mexico and Central America and bottoms out at 21,881 feet (6,669 meters), the 18th-deepest point on Earth. It marks the seam where the Rivera, Cocos, and Nazca plates dive beneath the North American and Caribbean plates. That same machinery produced Mexico's 1985 Michoacan earthquake and the 1992 Nicaragua tsunami.

Cayman Trough

Woods Hole Oceanographic Institution's submersible Alvin works the Cayman Trough often. In August 2022, Sabrina Douglas rode it down to the Beebe Vent Field to become the first Caymanian in the deep, past vents that blast mineral-rich water at 750 degrees Fahrenheit (400 degrees Celsius). It is the deepest known hydrothermal system on Earth.

But Alvin is certified only to 21,326 feet (6,500 meters), and the trough's floor lies at 25,217 feet (7,686 meters), the deepest point in the Caribbean Sea. That leaves a gap of about 3,900 feet (1,200 meters). No crewed submersible has closed it.

Aleutian Trench

In the summer of 2024, Fendouzhe ran 23 dives across the Aleutian Trench and the neighboring Kuril-Kamchatka Trench, and found something nobody expected. Tube worms and clams, thousands of them, feeding on methane instead of sunlight across 1,553 miles (2,500 kilometers) of seafloor. In the Kuril-Kamchatka, the colonies ran as deep as 31,275 feet (9,533 meters), the deepest animal communities ever recorded. Nature published the results on July 30, 2025. The team's deepest Aleutian stop, a site it named "Aleutian Deepest," came in at 22,539 feet (6,870 meters).

The trench's true floor sits 90 miles (145 kilometers) southwest of Buldir Island, at 25,663 feet (7,822 meters). Fendouzhe stopped 3,100 feet (950 meters) short. This is the only trench on the list in U.S. waters, and it rides the same fault that produced the 1964 Great Alaska earthquake, the second-largest ever recorded by modern instruments.

New Britain Trench

Planet Deep, at the bottom of the New Britain Trench, is the deepest point on Earth with no documented descent, crewed or robotic. It lies at 29,987 feet (9,140 meters), south of New Britain and west of Bougainville Island in the Solomon Sea, some 4,265 feet (1,300 meters) below the Aleutian's floor. The pressure down there tops 13,000 pounds per square inch.

German surveyors aboard SMS Planet charted it in 1910, and the neighborhood has been shaking ever since. It sits in one of the most seismically active regions on Earth, where the Solomon Sea floor plunges beneath the Pacific and Australian plates at steep angles and sets off frequent shallow quakes. Full-ocean-depth subs like Bakunawa and Fendouzhe favor stable, well-charted beds. A floor that shakes this often makes for a harder, more hazardous target.

Submersibles That Could Reach Them

Only three crewed submersibles have ever been rated to survive full ocean depth. The bathyscaphe Trieste made the first descent to Challenger Deep in 1960, with Jacques Piccard and Don Walsh aboard, and was retired six years later. James Cameron flew the Australian-built Deepsea Challenger to the same spot in 2012, then donated it to Woods Hole in 2013 so its engineering could feed the next generation of subs. A 2015 truck fire on Interstate 95 damaged it in transit, and it has not dived to full depth since.

That leaves two. The Triton 36000/2, built for Victor Vescovo in 2018 for $37 million and first named Limiting Factor, went to Gabe Newell's Inkfish research group in 2022 and became Bakunawa. China's Fendouzhe entered service in 2020, for a price it has never disclosed. The titanium sphere on the Triton is rated for 16,000 pounds per square inch, the squeeze at Challenger Deep, about what 292 fully loaded Boeing 747s would weigh pressing on the hull. One dive to that floor runs four hours down, four on the bottom, and four back up.

Money and Scheduling

In the end it comes down to money and scheduling. Governments do fund seismic work at the Manila and Middle America trenches, but that money buys fault maps, not crewed descents. The closest anyone has come to the Aleutian floor was a foreign sub. Two active full-ocean-depth vehicles exist on the planet, worth a combined $70 million-plus, and they stay booked. Vescovo's expeditions have touched the deepest point of more than fifteen trenches since 2018. Fendouzhe has reached eight more on its own. A single seat on one of Vescovo's Challenger Deep dives has run about $750,000 since 2020. These six trenches are simply further back in a very short line.