Urashima, the world's first autonomous underwater vehicle powered by fuel cells, recorded a continuous cruising distance of 220 km off the shore of Suruga basin in June 2004. A closed cycle fuel cell system developed by Mitsubishi Heavy Industries, Ltd. (MHI) is installed in the unmanned underwater vehicle, which incorporates various new ideas and technologies. This latest underwater vehicle features a number of novel functions, including acoustic remote control, weight and trim control system, and investigating and observing functions. At the sea trials, these functions have been confirmed together with a power supplying function by fuel cells, autonomous navigation control, and many other outstanding functions.