measuring depth

[Jolyonp@aol.com]

Hello everybody,
I certainly have enjoyed all the great e-mail on this site.  However, I have a
question that I hope some of you can help with.  I've been building unmanned
submersibles for a few years...each one is a bit better than the last.  I
operate them from a boat on the surface...I hope to make one good enough to
investigate sunken ships at some point.  My question is this:  I need a device
that measures the depth that my sub is operating at and then transmits the
information to a display on the surface.  This isn't a remote controled
boat...it is "hard wired".
Any ideas?
Thanks very much,
Jolyon Pegis