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(Image: Advanced Imaging and Visualization Lab, Woods Hole Oceanographic Institution)

Here we remember the pioneering in its heyday as the world’s deepest-diving vehicle. Sadly, Nereus (rhymes with serious) is now in pieces, crushed by the immense pressure in the fathomless depths of the , north-east of New Zealand.

Researchers lost contact with Nereus on 10 May at a depth of 9990 metres. It had just collected a sea cucumber. If contact is lost, the craft was designed to ascend to the surface automatically. Instead, only debris bobbed up, indicating a catastrophic implosion. The sub’s controllers hope that the fragments will provide clues as to exactly what went wrong.

Nereus was built in 2008 at the . For surveys of large areas, it operated as an autonomous, free-swimming robot. For close-up investigation and sampling of rocks and organisms on the sea floor, it was controlled via a tether to a support ship.