Nereus, the United States’ only full-ocean-depth submersible, was lost at sea on May 10, 2014. The unmanned and remotely operated vehicle was capable of reaching the hadal zone, the ocean region 6 to 11 kilometers deep, and was designed, built and operated by Woods Hole Oceanographic Institution (WHOI) in Massachusetts. Nereus was at a depth of 9,990 meters in the Kermadec Trench off New Zealand, the fifth-deepest ocean trench in the world, when it lost contact with researchers aboard the R/V Thomas G. Thompson. Debris later surfaced, which was recovered and determined to be the remains of the vessel. The debris indicated a catastrophic implosion, likely of one or more of the vehicle’s ceramic buoyancy spheres.