The Challenger Deep was explored by who?

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The Challenger Deep is the deepest known point in the ocean at the southern end of the Marianas Trench. It is named after the ship that first discovered it, the HMS Challenger that first recorded its depths in an expedition in 1872-76. Recent sonar mapping has further defined it carried out by the US Center for Coastal & Ocean Mapping.
Three descents have been attempted. The only manned descent was in 1960 by the Trieste, acquired by the US Navy. Unmanned research vehicles were sent in 1995 and 2009. One was Japanese, the other US. The US vehicle is operated by the Woods Hole Oceanographic Institution.