[quote=Incubus]Hydrophone upgrades: The first ones increase the radius you can detect subs. The highest upgrade increases the hydrophone detection range from 20 kms to 30kms.
That is not quite right. The hydrophone range is 34 km since 1939, no matter what kind of device is used. The upgrades just minimize the "deaf zone" behind the u-boat where your sonarman cant hear, and make the hydrophone more precise (SO gives you more precise readings). It has been discussed here:
http://www.subsim.com/radioroom/showthread.php?t=80804
Sonar: No idea about the upgraded sonars. But I'm guessing the upgrade(s) allow you to calculate ranges from farther out. So far, with the first sonar set I have been able to ping targets from 8000 meters away.
Actually, it si 7500m.