Gliders can "fly" underwater along slightly inclined paths. No propeller is required. A change in volume (generated by filling an external oil bladder) creates positive and negative buoyancy. Because of the fixed wings, the buoyancy force results in forward velocity as well as vertical motion. So gliders move on a sawtooth pattern, gliding downward when denser than surrounding water and upward when buoyant. Pitch and roll are controlled (by modifying the internal mass distribution) to achieve desired angle of ascent/descent and heading. The high efficiency of the propulsion system enables gliders to be operated for several months during which they max cover thousands of kilometers.
Presently Gliders are operated by research laboratories and no JCOMM or GOOS program have yet been officially set up to share expertise and data at global scales.