Recovery of a Lost Subsea Asset at Full Ocean Depth in the Mariana Trench (10,925 m ± 4) Using a Crewed Submersible

Abstract In 2019, the Deep Submergence Support Vessel Pressure Drop embarked on the third leg of the Five Deeps Expedition. Over the course of 10 days, the full ocean depth submersible Deep Submergence Vehicle Limiting Factor made a record five dives to the bottom of the Mariana Trench: four to the Challenger Deep, one to the Sirena Deep. The submersible was supported by three scientific landers, one of which became stuck on the seafloor at 10,925 m depth. Here we describe how, during the third dive of the campaign, the expedition utilized the submersible to rescue this lost asset from full ocean depth. The expedition was not only significant for its operational jump from single full ocean depth dives to multiple dives in a short space of time, but demonstrated that assets lost in the deepest 45% of the oceans are no longer irretrievable.