Hi Brian. There has been a lot of work done in developing AUV's
and although I'm not sure how useful it would be to use one as a "homing
pigeon", there are many uses for one.
With a small computer and a GPS unit on-board they can be programmed to
follow a pre-set path, at any depth desired. As for returning to the sub, if
it came to the surface at a pre-determined location, the sub could retrieve it
there easily.
This could be an interesting project for a Psubber if he has
some computer programming skill.
Like anything underwater......The battery is the first obstacle to
overcome. It's only as good as the power supply. Could be a fun project
though.
Frank D.