[djmcmath]

Ok, I'll admit to being a submariner. Let me clear some things up:
1 - Inverse square law applies to sound in water, too, just like common sense (and science) dictates it should. Further, there are also propogation losses due to interaction with surface and bottom as well as with suspended particles or other material in the water. Inverse square prop loss is really an unrealistic best case. Even in a carefully directed ping, the signal is attenuated pretty quick -- the logic that "focusing" a beam somehow makes it go farther works well for lasers because they're completely different than transducers.
2 - LF Active has some theoretical advantages, namely the range. However, there are other disadvantages that make it nearly useless, really.
3 - Submariners detest active. It gives away our position like nothing else. We detest all self-noise. Active sonar is the sort of thing that we use only in extremis, and only to the minimum extent absolutely required by the tactical situation.
4 - Worse even than a simple ping is a super-loud ping. Nobody fires a ping at max intensity. Not only is it unnecessary, it's tactically idiotic.
5 - Worse even than a really loud ping is an omni-directional ping. You may or may not find the guy you're looking for, but not only does he know where you are, so do his 6 buddies floating nearby.


Your Friendly Local Submariner, now leaving communications depth...