http://www.subsim.com/radioroom//arc.../t-110619.html
http://files.filefront.com/U42HydroH.../fileinfo.html
(EDIT: this is an upscaled version of the original file - it didn't work on my W7 system right now.
I've uploaded the original small screen file - valid link is three postings down)
There are some better tutorials and techniques around now, but mine was the first one.

And it shows the result of the calculations to be good enough to successfully attack an invisible contact.
It's a Bink file - compressed with the radgame tools (freeware) three times as small as a WMV would have been. The Bink player is included, therefore it's an EXE.
Esc to end the clip, Spacebar to pause.