An ROV developed for survey of the sea bottom over a wide area can be operated both as a towed and a self-propulsive vehicle. Called DELTA, the shape is similar to a delta wing airplane. The vehicle has two-propellers and weight shift apparatus as actuators. The control scheme for the towing mode is different from that for the self-propulsive mode. The direction of DELTA in the towing mode should coincide with that of the mother ship and only the depth is controlled by the trim weight. In the selfpropulsive mode the direction is controlled by the difference between the right and left thruster, and the depth is controlled by the pitch moment generated by the change of the thrust, the motion control is mainly done by the thrusters and the trim weight works to maintain static balance. The dynamic motions of DELTA were investigated theoretically and experimentally. The excellent performances of the vehicle were verified in this study.