Named Nereus, the mini-sub was one of the most advanced in the world and worth a cool $8 million.
Scientists are now confident it lies over six-miles-deep in a trench off the coast of New Zealand.
The BBC reports debris found at the surface indicates at least part of the ROV most likely imploded under the 16,000 pounds of pressure that accompanies that depth.
The Woods Hole Oceanographic Institution built Nereus.
In a release, chief scientists Timothy Shank praised the work done by the sub. "Nereus helped us explore places we've never seen before and ask questions we never thought to ask," he said.
Nereus was one of only four subermsibles to visit the deepens place on the planet, the Mariana Trench.
The Cape Cod Times reminds us this isn’t the first loss for Woods Hole. In 2010, Nereus predecessor ABE disappeared off the coast of Chile.