The bathyscaphe Trieste—a deep-diving vessel designed around a pressure-resistant crew sphere and a buoyant float—was launched in Italy. It was part of Auguste Piccard’s effort to build submersibles that could reach far deeper than earlier bathyspheres. This launch set the technical foundation for later attempts to reach the deepest ocean trenches.
The U.S. Navy acquired Trieste to support a growing deep-submergence program that combined science goals with practical interests like deep-ocean operations and submarine rescue research. Under U.S. management, the craft was prepared for more demanding missions than its earlier Mediterranean work. This purchase made a large, well-funded trench-diving effort possible.
Project Nekton began as a planned sequence of test and deep-water dives near Guam to push Trieste toward trench depths. The program used repeated dives to check endurance, equipment reliability, and navigation methods in an era before GPS. These steps were necessary before attempting the most difficult target: Challenger Deep.
Jacques Piccard and U.S. Navy Lt. Don Walsh piloted Trieste to the seafloor of Challenger Deep in the Mariana Trench, the deepest known point in the ocean. The dive proved that a crewed vehicle could survive hadal pressures (the extreme pressures in the deepest ocean zone) and return safely. For decades, it remained the only crewed visit to the bottom of Challenger Deep.
After its landmark trench dives, Trieste was eventually taken out of service by the U.S. Navy. Its retirement reflected both the limits of the bathyscaphe approach and the shift toward newer, more maneuverable deep-submergence designs. Even so, Trieste’s 1960 dive remained a benchmark that later programs aimed to match or surpass.
The U.S. Navy brought Trieste II into official service and assigned it a hull number (X-1), continuing the Trieste lineage in a new vehicle. Trieste II supported testing and operations for the Navy’s deep-submergence capabilities, emphasizing practical deep-ocean tasks rather than record-breaking depth alone. This helped keep crewed deep operations active even as Challenger Deep remained out of reach.
Trieste II was redesignated DSV-1 (Deep Submergence Vehicle), reflecting its formal role within the Navy’s deep-submergence fleet. The change marked the Navy’s move toward standardized deep-submergence platforms and support systems. This period helped refine crew training, procedures, and equipment used in later deep-ocean vehicles.
Trieste II conducted a major recovery operation from more than 16,000 feet, demonstrating that crewed submersibles could do demanding work at great depth, not just scientific observation. The mission was later declassified, and the unit received recognition for the achievement. This reinforced the idea that deep-diving vehicles could support national objectives as well as research.
Japan’s deep-submergence program advanced with sea trials of the crewed submersible Shinkai 6500, including dives beyond 6,400 meters and a reported 6,527-meter trial dive. This did not reach Challenger Deep, but it expanded routine crewed access to much of the deep ocean for research. It also showed that multiple nations were investing in reliable, repeatable human dives to extreme depths.
The Japanese robotic vehicle Kaikō reached the bottom of Challenger Deep, becoming the first craft to do so since Trieste—though without a human crew. This showed how remotely operated vehicles could survive full-ocean-depth pressures and collect data where crewed systems had not returned. The event also highlighted a growing gap between uncrewed and crewed hadal exploration.
The hybrid remotely operated/autonomous vehicle Nereus reached Challenger Deep and transmitted video and scientific observations from the seafloor. Like Kaikō, it reinforced that uncrewed systems could repeatedly access the deepest ocean. At the same time, it kept attention on the long-standing challenge of returning humans safely to Challenger Deep.
James Cameron piloted Deepsea Challenger to the bottom of Challenger Deep, completing the first crewed visit since 1960 and the first solo crewed descent. The mission gathered imagery and samples and demonstrated a new generation of engineering approaches for full-ocean-depth human dives. It marked a clear turning point: Challenger Deep manned exploration restarted after a 52-year gap.
Bathyscaphe Trieste and subsequent Challenger Deep manned exploration (1957–2012)