This glider works by using a bladder to change its density to water (same weight, but different volume). When it sinks or surfaces, the long wings cause it to glide forward. With a small change of the bladder, the glider can travel huge distances. They are rather slow and have limited mobility, but work really great for high efficiency long distance traveling.
"Another invention from Osaka university is the underwater glider manuevered via radio control it moves easily underwater."