There are concerns about the impact that global warming will have on our environment, and which will inevitably result in expanding deserts and rising water levels. AUVs (Autonomous Underwater Vehicle) were considered and chosen, as the most suitable tool for conducting surveys concerning these global environmental problems. JAMSTEC has started to build a long range cruising AUV. An AUV, named "URASHIMA" was built in1999, and sea trials have been held since 2000. At the end of February 2005, the vehicle was able to cruise autonomously and continuously for 317km. Recently the vehicle has begun to undertake cruises for scientific applications. These applications require precise maneuvering of the vehicle for detailed investigations. For high performance maneuvering of the vehicle, it is necessary to design a control system based on a mathematical model for the vehicle. Since the vehicle was built, PI control has been adopted. In order to improve control performance, the motion controller can be design by means of a model-based approach (e.g. LQI control). This paper describes the mathematical model of the vehicle, experimental results of maneuverability obtained with the AUV "URASHIMA" during the sea trials, the design method of the motion controller, and shows calculated results.