What I'd be interested in knowing is what information the UIM-9X would need before it was fired.
Conventional AIM-9s are already locked onto the target before they fire. The seeker is aimed by the radar in most cases. The seeker can search for a target independently, but this is slower. How much slower? I have no idea...
So, when the UGM-9 breaks the surface, can it find a target without hellp? 90 degrees off-boresight gives it the capability to see a low flying target for a few moments, but it doesn't guarantee that the seeker will search the right part of the sky in the time it has. My guess is that it can't, or at least can't reliably. If that guess is right, then the missile will need to have a bearing assigned by the sub. If it has that info, it can nose over in the right direction. Presumably, the scan pattern can be narrowed to increase the chance it finds the target.
__________________
|