Nereus was sent to complete the first systematic study of the Kermadec Trench.
Thirty days into the 40-day mission, about seven hours into a nine-hour dive, communications with Nereus was lost. When standard emergency recovery protocols were unsuccessful, the team initiated a search near the dive site. They then spotted several pieces of debris on the surface nearby later identified to be parts of Nereus, indicating a catastrophic implosion.
Nereus was a flagship ocean explorer for the US science community.