The unmanned submarine that imploded in the Kermadec Trench in 2014 was Nereus.
Nereus was a hybrid remotely operated vehicle built and operated by the Woods Hole Oceanographic Institution. Its unusual design allowed it to work either as a tethered vehicle controlled from a research ship or as an autonomous, free-swimming robot. It was engineered for full-ocean-depth missions and had previously reached 10,902 m in the Mariana Trench in 2009.
On 10 May 2014, Nereus was exploring the Kermadec Trench northeast of New Zealand at roughly 9,990 m when communications stopped. Debris later recovered at the surface indicated that part of the vehicle had suffered a catastrophic implosion under the immense pressure. At that depth, pressure can exceed 1,000 times the pressure at sea level.
Nereus was not the same vehicle as Kaiko, Japan’s remotely operated vehicle used in earlier deep-ocean missions, or ABISMO, another Japanese system. Despite its loss, the expedition produced valuable observations of hadal ecosystems, including deep-sea animals and biological activity in one of Earth’s most extreme environments.