Well, correct me if I'm wrong but I understand that the ping sound is just sound played when enemy ping hits the boat, so if we changed it, then EVERY ping would sound like missile launch :-).
(Edit: after looking into sfx.agg I see that not every ping - just every torpedo ping
IF we could add custom ping sound to active sonar, the we could make it missile launch, but there is no such thing in database... most probably every active mounted on a torpedo calls for torpedo ping sound.
If so :hmm: what sound would be called for active sonar mounted on a missile ?

maybe nothing, or game crash ?

so better first we check if it is possible at all, later we could discuss how should it look (sound) like

)
And if we assigned a crew comunicate as missile sound, then I guess the missile would say it over and over in flight, instead of normal flying missile sound :-). It would be audible in 3D view, but not on other sub.
The thing we didn't make, was to assign BB sound file to a SUBROC missiles, this is the sound heard in BB sonar station on bearing of the contact. If we assigned a sound of a distant underwater missile launch to it (or rather missile motor working underwater) then there should be no more problems with discriminating it from any other target, you would just hear the missile at the bearing. Best would be sound already present in game, this would require only database change. If we don't find it (because it has to be underwater missile sound) then we would have to add it to sfx.agg which means more complicated install and changes outside database folder... but we probably have to do it anyway to update USNI reference database.
P.S. I though for a moment that we can use BB_shkval sound, shkval underwater, but it's wery poor choise... it sounds like a missile combined with a torpedo, so you hear missile with rotating propellers

But we could use it and add a stand-alone second little mod with better skhval sound, which can be used both with stock game and modded.
We can try also just missile launch sound, who knows maybe it would work ok... edit: probably wouldn't, seems I can't use fx_xxx sound as bb_xxx sound...
Best would be combined sound, beginning from torp launch with missile launch later, processed to sound like underwater. Then if you listened on the bearing and the distance wasn't long, you could actually hear whole missile launching sequence. I wish Finiteless was around... wonder what happened with him ? :hmm: