A change in volume -generated by filling an external oil bladder or moving a piston- creates positive and negative buoyancy. Because of the wings, the buoyancy force results in forward velocity as well as vertical motion. Then, they move on “a sawtooth” pattern through the water column, gliding downward when denser than surrounding water and upward when buoyant. Pitch can be controlled by modifying the internal mass distribution. Wings are fixed and gliders automatically align the positions of the center of buoyancy and the center of gravity to achieve desired angle of ascent/descent. A rudder is used for the heading / roll control and navigation through a waypoints list. Depth rate is limited (for now) up to 1000 m.for commercial models.