To supply the power needed, closed-cycle fuel cell
systems have for some time been under development; but favorable results had not been obtained owing to issues such as the inability to achieve compact system size because of the need for gas circulation equipment and humidifiers to add dampness to the gas, compounded by the inability to prevent minuscule leaks of hydrogen gas.
According to Kyodo, the Urashima, which employs a hydrogen-powered, closed-cycle fuel cell
, maintained a depth of 800 meters, traveling in 25-kilometer laps at a speed of five kilometers per hour for a period of 56 hours.
The underwater vehicle Urashima uses a closed-cycle fuel cell
, using hydrogen as fuel, and is the first unmanned underwater vehicle to use fuel cells, Aoki said.