https://newatlas.com/us-navy-mk29-rebreather-test/54863/

The US Navy has begun pool testing of its new MK29 Mixed Gas Rebreather designed to conserve helium during deep sea dives below 170 ft (52 m). The test dives took place at the Naval Surface Warfare Center Panama City (NSWC), Florida, where it was developed under a project sponsored by the Office of Naval Research Global (ONR Global) TechSolutions program.