Editing Challenger Deep (section)

===1951 – SV HMS ''Challenger II''===
[[File:Gaskell HMS Challenger II.jpg|thumb|Chief Scientist [[Tom Gaskell]], left, aboard [[HMS Challenger (1931)|HMS ''Challenger II'']], 1951]]

Seventy-five years later, the 1,140-ton British survey vessel [[HMS Challenger (1931)|HMS ''Challenger II'']], on her three-year westward [[circumnavigation]] of Earth, investigated the extreme depths southwest of Guam reported in 1875 by her predecessor, HMS ''Challenger''. On her southbound track from [[Occupation of Japan|Japan]] to [[New Zealand]] (May–July 1951), ''Challenger II'' conducted a survey of the [[Mariana Trench|Marianas Trench]] between Guam and [[Ulithi]] atoll, using seismic-sized bomb-soundings and recorded a maximum depth of {{convert|5663|fathom|0}}.{{citation needed|date=March 2021}} The depth was beyond ''Challenger II''{{'s}} [[echo sounder]] capability to verify, so they resorted to using a taut wire with "140&nbsp;lbs of scrap iron", and documented a depth of {{convert|5899|fathom|0}}.<ref name="Ritchie, G.S. 1958 p.225">Ritchie, G. S., ''Challenger, the Life of a Survey Ship'', Abelard-Shuman (1958), p. 225</ref> The Senior Scientist aboard ''Challenger II'', [[Thomas Gaskell]],<ref>{{Cite web |title=Marine Gazetteer Placedetails - Gaskell Ridge |url=https://www.marineregions.org/gazetteer.php?p=details&id=7319 |url-status=live |website=Marineregions.org |access-date=23 January 2023 |archive-date=23 January 2023 |archive-url=https://web.archive.org/web/20230123230233/https://www.marineregions.org/gazetteer.php?p=details&id=7319 }}</ref> recalled: <blockquote>[I]t took from ten past five in the evening until twenty to seven, that is an hour and a half, for the iron weight to fall to the sea-bottom. It was almost dark by the time the weight struck, but great excitement greeted the reading...<ref>{{Cite book |last=Gaskell |first=Thomas F. |title=Under The Deep Oceans: Twentieth Century Voyages of Discovery |publisher=Eyre & Spottiswood |year=1960 |edition=1st |pages=121}}</ref></blockquote>In New Zealand, the ''Challenger II'' team gained the assistance of the Royal New Zealand Dockyard, "who managed to boost the echo sounder to record at the greatest depths".<ref name="Ritchie, G.S. 1958 p.225"/> They returned to the "Marianas Deep" (sic)<ref>Gaskell, T. F., "HMS Challenger's World Voyage 1950–52", Part I. Atlantic & Pacific Oceans, International Hydrographic Review, Vol. XXX, no. 2 (2018), p. 119</ref> in October 1951. Using their newly improved echo sounder, they ran survey lines at right angles to the axis of the trench and discovered "a considerable area of a depth greater than {{convert|5900|fathom|0}}" – later identified as the Challenger Deep's ''western'' basin. The greatest depth recorded was {{convert|5940|fathom|0}},<ref>Ritchie, G. S., ''Challenger, the Life of a Survey Ship'', Abelard-Shuman (1958), p. 229</ref> at {{Coord|11|19|N|142|15|E}}.<ref>{{cite journal |last=Fujioka |first=K |display-authors=et al |title=Morphology and origin of the Challenger Deep in the Southern Mariana Trench |journal=Geophysical Research Letters |volume=29 |issue=10 |date=18 May 2002 |pages=10–1–4|doi=10.1029/2001GL013595|bibcode=2002GeoRL..29.1372F |s2cid=129148518 }}</ref> Navigational accuracy of several hundred meters was attained by celestial navigation and [[LORAN|LORAN-A]]. As Gaskell explained, the measurement <blockquote>was not more than 50 miles from the spot where the nineteenth-century ''Challenger'' found her deepest depth [...] and it may be thought fitting that a ship with the name ''Challenger'' should put the seal on the work of that great pioneering expedition of oceanography.<ref name=":1" /></blockquote>The term "Challenger Deep" came into use after this 1951–52 ''Challenger'' circumnavigation, and commemorates both British ships of that name involved with the discovery of the deepest basin of the world's oceans.[[File:Kaliningrad 05-2017 img62 Ocean Museum.jpg|thumb|Research vessel ''Vityaz'' in [[Kaliningrad]] "Museum of world ocean"]]