IIRC they developed a kind of homing device for divers, with a beacon
that should hang beneath the boat.

For navigation, the compass is it unless you can afford and carry an
inertial navigation system.

For homing (which is a whole different problem: yer trying to relocate a
known position) there are a variety of devices, most modern ones relying
on sound.

With some practice, a compass is surprisingly accurate and reliable.

My local dive shop used to sell a device that was a "homing signal"
type device for navigation.  It was two part, one part signal generator
that put out some type of signal and the other part receiver that
the diver wore on the wrist.   The signal generatoring device
had a clip on it and you attached it to something like the
anchor line of the dive boat.  You could then use the wrist
mounted device to find your way back to the anchor line where
the singal device was attached.

i can't remember the name of the device, but it was rubber
coated and orange in color.   It was orignally designed for
the navy divers so they could find their way back in no visibility
or at night w/o lights.   There was a military version that
apparantly had some sort of GPS with a floatable antenna
and gyro to keep track of position after GPS position fix.
But this was a military version and I don't think available
to the general public.

Like I said, I can't remember the name of it.  I think it was
about $900 or so.   I do know that during the craze that the
FBI was worried about terrorist trying to plant bombs using
scuba gear, that they got real paranoid about this device
and I think issued a court order to turn over names of people
who purchased it....

This isn't the item I was talking about above, but in trying
to find the name of it, I found this interesting toys...

Diver Navigation Equipment
Cobra-Tac™ Navigation & Mapping Console
http://www.rjeint.com/pdf/cobra_tac.pdf

Aqua Map
http://www.desertstar.com/newsite/positioning/diver/aquamap2.html

Sport & Scout scuba homing devices
http://www.desertstar.com/newsite/sport/sportscout.html