The submersible that first reached the Challenger Deep was Trieste. On 23 January 1960, Trieste carried Swiss oceanographer Jacques Piccard and U.S. Navy lieutenant Don Walsh to the bottom of the Mariana Trench’s Challenger Deep, the deepest known point on the ocean floor.
The bathyscaphe descended to approximately 10,916 metres, although later surveys have produced slightly different measurements. Trieste’s design used a pressure-resistant crew sphere, gasoline-filled buoyancy tanks, and iron-shot ballast. The gasoline provided lift because it is less dense than seawater, while ballast allowed the vessel to sink and be released for the return ascent.
Trieste was designed by Swiss scientist Auguste Piccard, Jacques Piccard’s father, and built in Italy. The United States Navy purchased it in 1958 and used it for Project Nekton, a series of deep-ocean dives near Guam. The answer is sometimes confused with Deepsea Challenger, which carried filmmaker James Cameron on a solo Challenger Deep dive in 2012. Alvin is another famous research submersible, but it never made the first descent to the trench’s deepest point.