Hello TDW,
I found the 'AI torpedo' thread for SH4 (at SH4 we have no torpedo for AI ships) and here modders found the solution to shoot torpedo from destroyers and PT-boats.
Of course this solution is not perfect but maybe SH5 has better environment to add new implementation of your FX mod.
Link:
http://www.subsim.com/radioroom/show...=154068&page=8