There have also been a couple of successful underwater firings of the AIM-9X, with the target set apparently intended to include small surface vessels in addition to air targets.
I brought this up a while ago on another forum and the response I got seemed to indicate that while such developments were interesting and may give a submarine some additional flexibility in certain situations, it would be more of a last resort when it comes to responding to ASW helos, as the launch of the missile would give away sonar data to any other ASW platforms in the area. From my understanding a dedicated ASW package is going to include multiple helos/surface vessels running search patterns, and for a submarine to fire off a weapon in the midst of that would be highly hazardous.
One of the others on here with more knowledge might be able to tell you more. Underwater AIM-9X