Simple question: Shouldn't it be possible to use similar geometries that are used to make "stealth" aircraft nearly invisible to radar to make "stealth submarines" nearly invisible to sonar? The same principles should apply, right? Is this done? If not, why? My only guess is that the decrease in hydrodynamical performance would just be too great to justify it.

The idea was proposed to the Navy, but rejected due to the loss in speed that would result.

 

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Ah. Just as I suspected.

Active sonar isn't used all that much, since it gives away the position of everything within range. Subs are already made to be stealthy. A material that made them invisible to active sonar would also have to keep them quiet in order to be invisible to passive sonar.

bah, use active panels and peizo electric sensors to dampen the sonar/ project the sound on the other side. shape would be irrelevant, crew would be deaf.

There are some differences I think, largely because the internal structure of a sub tends to resonate and produce noise. So there's more of an emphasis on things like internal anechoic chambers (which don't produce echos) and trying to damp the super structure.

i'm not convinced that padding on the inside of the sub will fix the problem, you still have solid relfections off the hull. the angled panels are used to scatter the sonar reflections. i think that anything like military grade armouring will have horrid acoustic problems.

even a thin compressible layer stuck on the outside of the hull isn't perfect. it can end up with cavitation problems at high speed.

Padding on the inside, as well as placing machinery on isolated "rafts" inside the hull, prevents noise from radiating outwards. Most submarines are detected with passive sonar, after all - active sonar is like turning on a flashlight in a dark room: you find the enemy, but he knows where you are too.