Underwater vehicles capable of self-propulsion are described. An underwater vehicle includes a cross-flow turbine including two or more foils spaced apart from a main shaft. The foils have a pitch that is adjustable under control of a pitch control mechanism. The underwater vehicle also includes a frame supporting the main shaft. The frame enables rotation of the cross-flow turbine. The underwater vehicle additionally includes a generator-motor set including rotor and stator elements. The rotor element is in rotary communication with the main shaft.