Trieste was the first manned vessel to reach the bottom of the Challenger Deep. On 23 January 1960, the bathyscaphe carried Swiss explorer Jacques Piccard and U.S. Navy lieutenant Don Walsh to the deepest known part of the Mariana Trench.
The dive was part of Project Nekton, a U.S. Navy program of deep-ocean exploration. Trieste was designed by Swiss scientist Auguste Piccard and built in Italy. Its crew sphere was suspended beneath a buoyant hull filled with gasoline, while iron ballast allowed the craft to descend and later rise.
The descent took about 4 hours and 47 minutes. Piccard and Walsh spent roughly 20 minutes on the seafloor before beginning the ascent. A window pane cracked under the immense pressure, but the pressure sphere remained intact and the men returned safely.
Later vehicles made important repeat dives. Deepsea Challenger carried James Cameron to the bottom in 2012, while Nereus was an unmanned vehicle. Neither changed Trieste’s status as the first crewed vessel to reach Challenger Deep.