Challenger Expedition,
a circumnavigating scientific exploration of the open sea sent out by the British government in 1872-1876. In 1872 the "Challenger," a corvette of 2,306 tons, was completely fitted out and furnished with every scientific appliance for examining the sea from surface to bottom. The ship was given in charge to a naval surveying staff, under Captain Nares, and to a scientific staff, with Professor Wyville Thomson at their head, for the purpose of sounding the depths, mapping the basins, and determining the physical and biological conditions of the Atlantic, the Southern and the Pacific Oceans. Between the Admiralty Isles and Japan the "Challenger" made her deepest sounding, on March 23, 1875, 4,575 fathoms, then the deepest sounding on record except two. It is interesting to note here that the United States surveying ship "Nero," in an expedition extending from April 22, 1899, to Feb. 11, 1900, made the two deepest soundings on record, 5,160 and 5,269 fathoms, both in the Pacific Ocean.
Entry from Everybody's Cyclopedia, 1912.