Underwater gliders work by being buoyantly nearly neutral while near the water’s surface, so that they sink slowly down. Very slowly – full steam ahead is under one knot. As they sink, an internal weight is shifted toward the lateral direction the vehicle should go – if you want to go straight, just shift the weight forward to tilt the nose down a bit. Then to rise, pump an oil contained inside the hull into external sacks – this simple maneuver increases the craft’s volume, and thus lowers its density just enough that now the surrounding water wants to push it upward.
Original: craschworks - comments

Awesome
Date: 2008-11-25 02:29 pm (UTC)Instead of sinking like a rock or floating up like a balloon, these clever little creatures glided forwards in both the up and the down cycle.
Pretty neat huh? The same concept can be done with lighter than air ships as well.
Now I'm starting to think -did I read about this in your journal originally a year or so ago?