This survey recorded the deepest part of the trench using echo sounding, a more precise and easier way to measure depth than the sounding equipment and drag lines used in the original expedition. In 1951, about 75 years after its original discovery, the entire Mariana Trench was surveyed by a second Royal Navy vessel, captained by George Stephen Ritchie (later Rear Admiral Ritchie) this vessel was also named HMS Challenger, after the original expedition ship.Murray was one of the expedition scientists. A 1912 book, The Depths of the Ocean by Sir John Murray, records the depth of the Challenger Deep as 31,614 ft (9,636 m), reporting the sounding taken by the converted navy collier USS Nero in 1899.The reported depth was 4,475 fathoms (26,850 ft 8,184 m) at Template:Coord, based on two separate soundings. This first sounding was made on 23 March 1875 at station 225. The HMS Challenger expedition (December 1872 – May 1876) first sounded the depths now known as the Challenger Deep.Over many years, the search for the point of maximum depth has involved many different vessels. History of depth mapping from the surface These expeditions measured very similar depths of 10,898 to 10,916 metres (35,755 to 35,814 ft). In March 2012 a manned solo descent was made by the deep-submergence vehicle Deepsea Challenger. This was followed by the unmanned ROVs Kaikō in 1995 and Nereus in 2009. The first descent by any vehicle was by the manned bathyscaphe Trieste in 1960. Only four descents have ever been achieved. A 2014 study concludes that with the best of 2010 multibeam echosounder technologies a depth uncertainty of ☒5 m (82 ft) (95% confidence level) on 9 degrees of freedom and a positional uncertainty of ☒0 to 25 m (66 to 82 ft) (2drms) remain and the location of the deepest depth recorded in the 2010 mapping is 10,984 m (36,037 ft) at Template:Coord ( Template:Coord). Further soundings made by the US Center for Coastal & Ocean Mapping in October 2010 are in agreement with this figure, preliminarily placing the deepest part of the Challenger Deep at 10,994 m (36,070 ft), with an estimated vertical uncertainty of ±40 m (131 ft). The sonar system uses phase and amplitude bottom detection, with a precision of 0.2% to 0.5% of water depth this is an error of about 22 to 55 m (72 to 180 ft) at this depth. June 2009 sonar mapping of the Challenger Deep by the Simrad EM120 (sonar multibeam bathymetry system for 300–11,000 m deep water mapping) aboard the RV Kilo Moana indicated a depth of 10,971 metres (35,994 ft). According to the August 2011 version of the GEBCO Gazetteer of Undersea Feature Names, the location and depth of the Challenger Deep are Template:Coord and 10,920 m (35,827 ft) ☑0 m (33 ft). The depression is named after the British Royal Navy survey ship HMS Challenger, whose expedition of 1872–1876 made the first recordings of its depth. It is located in the ocean territory of the Federated States of Micronesia, 1.6 km (1 mi) from its border with ocean territory associated with Guam. The closest land to the Challenger Deep is Fais Island (one of the outer islands of Yap), 287 km (178 mi) southwest, and Guam, 304 km (189 mi) to the northeast.

Its bottom is about 11 km (7 mi) long and 1.6 km (1 mi) wide, with gently sloping sides. The Challenger Deep is a relatively small slot-shaped depression in the bottom of a considerably larger crescent-shaped oceanic trench, which itself is an unusually deep feature in the ocean floor. It is in the Pacific Ocean, at the southern end of the Mariana Trench near the Mariana Islands group. The Challenger Deep is the deepest known point in the Earth's seabed hydrosphere, with a depth of 10,898 to 10,916 m (35,755 to 35,814 ft) by direct measurement from submersibles, and slightly more by sonar bathymetry. Thumb|300px|Location of Challenger Deep within the Mariana Trench and Western Pacific Ocean

Challenger deep book