Here's a cool little utility made for SH4 "Bearing to AOB + Sonar Fix.
Read the first post, and follow the link to FF to grab the utility. It really helps to set up a great torpedo attack, since the DDs and DEs just always seem to locate you while running silent, and deep.
http://www.subsim.com/radioroom/show...+%2B+Sonar+FIX
Really helps with getting in close initially and if you're careful, you can really spring a suprize on them, and be gone like a ghost in the night before they know what hit them.