The PASS vehicle uses the temperature delta to provide displacement changes to the vehicle which allows the vehicle to glide up and down thru the water column. In PASS the working fluid is heavy water. This concept was of interest to DARPA's SBIR program but unfortunately the requirerment for the primary researcher to be a US citizen was not met and the project was not developed.
A couple of links to related developments.
Copyright © 1988, 2006 Tony Bigras.