An underwater robot, Aquarobot, is a robot for underwater inspections in place of divers in port construction works. The Aquarobot has sixlegs similar to those of an insect, which are arranged in an axially symmetric manner. It is able to perform various kinds of inspection tasks while walking on a sea bed up to a depth of 50 m. A TV camera equipped with an ultrasonic range finder is attached at the tip of a manipulator of the robot for measuring the dimensions of an object on the CRT.
　The robot is navigated with the aid of a long base line ultrasonic positioning system that is newly developed for the robot. The accuracy of the system is about 10 cm. The robot have function to make a accurate depth map of sea bed by using both the positioning system and a depth meter.
　Its usefulness was confirmed through several field tests. The test results were as follows: The walking speed on a rubble mound at a water depth of 50 m was 1.4m/min. and the positioning accuracy was 1 to 35 cm. The depth measurement by the robot was as accurate as one by human divers.