Another interesting alternative to a traditional motor is the "Slocum Glider", which dives and propels itself through the water by pumping oil between its body

Another interesting alternative to a traditional motor is the "Slocum Glider", which dives and propels itself through the water by pumping oil between its body and an external bladder. http://www.whoi.edu/main/slocum-glider http://www.whoi.edu/main/slocum-glider http://en.wikipedia.org/wiki/Underwater_glider http://en.wikipedia.org/wiki/Underwater_glider