Underwater Glider
From HackerSpace SD
These underwater vehicles use changes in boyancy to control their depth and use any change in depth as a means of propulsion much like a traditional glider in the air.
We could build an underwater glider that uses GPS and a digital compass to autonomously do just about anything we can think of. If we combine this with Solar power (only useful when it surfaces) we could have it circumnavigate the globe using minimal energy.
