submarine vessel designed to operate at great depths. The first such vessel, invented in 1947 by the Swiss physicist Auguste Piccard, explored the ocean bottom at a depth, in 1954, as great as 4000 m (13,125 ft) and operated under water pressure of 0.42 metric ton/sq cm. The bathyscaphe Trieste, built in 1953, set a world record on Jan. 23, 1960, when it descended 10,916 m (about 35,814 ft) to the bottom of the Mariana Trench, deepest known point in the oceans, 402 km (250 mi) southwest of Guam. It withstood pressure of 1.17 metric tons/sq cm at that depth. The craft, which carried gasoline for buoyancy and iron pellets for ballast, descended when water was pumped into air tanks at either end and ascended when water was pumped out and the pellets released. The dive, manned by the Swiss scientist Jacques Piccard (1922–    ), the son of Auguste Piccard, and Lt. Donald Walsh of the U.S. Navy, yielded important geophysical information. The Trieste was also used in the unsuccessful search for the hull of the nuclear submarine USS Thresher, which had plunged 2560 m (8400 ft) to the ocean floor 354 km (220 mi) off the coast of New England in April 1963. Although the hull of the Thresher was not found, some pieces of its equipment were later recovered by the Trieste. See DEEP-SEA EXPLORATION,; GEOPHYSICS,.