But it appears that the Raytheon is working on an underwater surface to air missile based on the AIM-9X.

It appears that they are looking at autonomous operation of the missile after launch from a sub, as opposed the the German IDAS system which maintains a fiber optic link to the missile.

There are a number of reasons that I am dubious of such a system, the ability of a submarine to get targeting data regarding an airborne threat and the fact that the AIM-9X has pretty poor kinematics compared to other IR AAMS, because its motor is based on a 50 year old airframe.

On the other hand, this weapon is just about perfect for terrorists: Drop the canister off the end of a boat, and shoot down a passenger plane coming into land at a seaside airport.