On 31 May, a robotic sub named the Nereus reached a depth of 10,902 metres at Challenger Deep in the Marianas Trench. This is the deepest known part of the ocean.
In 1960 The Trieste, a bathyscaphe, reached a depth of 10,916 metres. Inside were Jacques Piccard and Don Walsh. Their 9 hour voyage only spent 20 minutes on the seabed. 35 years later a Japanese remotely controlled vehicle, the Kaiko, diving in the same area reached 10,911 metres. Sadly the Kaiko was later lost on an unrelated dive when her cable snapped. So Nereus is currently the only vehicle capable of working at such depths. In addition to operating via a fibre optic tether, it can also be switched into a free swimming, autonomous mode.
The Challenger Deep is in the western Pacific, near Guam and is 2 km deeper than Everest is high. Apart from the Nereus, the other deep-rated submersibles can only get down to about 6500 metres,w hich covers 95% of the ocean floor.
You can read the story from which the pictures came from the BBC website.
