Nereus (underwater vehicle)

Nereus was a hybrid remotely operated vehicle (HROV) designed and built by the Woods Hole Oceanographic Institution (WHOI). It was capable of operating both as an autonomous underwater vehicle (AUV) for broad area surveys and as a remotely operated vehicle (ROV) tethered to a surface ship for detailed exploration and sampling. Its hybrid capability allowed scientists to survey large areas of the deep ocean and then focus on specific sites of interest with the greater precision and data transfer capacity of a tethered ROV.

Nereus was notable for reaching the Challenger Deep in the Mariana Trench, the deepest known point in the ocean, in 2009. This made it only the second vehicle to ever reach this depth, following the bathyscaphe Trieste in 1960. The vehicle transmitted live video from the bottom of the trench and collected samples.

The key technologies that enabled Nereus to operate at such extreme depths included its use of ceramic spheres to house its electronics, lightweight lithium-ion batteries for power, and a thin, hair-like fiber optic tether for communication and control when in ROV mode.

Nereus was lost at sea on May 10, 2014, while exploring the Kermadec Trench northeast of New Zealand. The cause of the loss was attributed to a catastrophic implosion at depth.