On 31 May 2009, the deepest place in the world ocean was visited by the new hybrid unmanned submersible, Nereus. It landed on the seafloor of the Challenger Deep-at an amazing 35,768 feet down-in the Mariana Trench, spending ten hours there. The vehicle was designed, built, and operated by the Woods Hole Oceanographic Institution (WHOI) and can be operated either as a tethered remotely operated vehicle (ROV) or as an autonomous untethered vehicle (AUV).
The Nereus was not the first. In January 1960 the Navy's bathyscaph Trieste, a manned submersible, made a dive there to a depth of 35,800 feet. Although she remained on the bottom for 20 minutes, no photographs were taken because of a persistent sediment cloud stirred up by her landing.