This paper describes the objectives, organizations and research results of an international joint research project on an underwater walking robot conducted at the Port and Harbour Research Institute in Japan and the Naval Postgraduate School in the US . The main purpose of this project has been to investigate several scientific research questions in the US side and to enhance the capability of the existing six-legged underwater walking robot, AQUAROBOT. The period of this pro- ject was three years from February 1992. Almost two dozen researchers have been involved in the pro-ject. The research results briefed in this paper include smooth motion planning for rigid body ro- bots, versatile extended gait planning, dynamic foot motion planning, experiments with the real A-QUAROBOT, and virtual reality simulation model. By using newly developed real-time software, the AQUAROBOT for overground test can walk at the speed of 15m/min. on the flat terrain. It is twice of that by the conventional software.