Thanks guys.
Learning the mission editor sure is an exercise in experimentation.
Using depth charges could inherently sink a sub, sure. But I don't want it to be a "deliberate" act of sinking.
I think it's gonna take me awhile to get this mission playable. I may be biting off more than I can chew for a first foray into mission creation. Perhaps I should step back and make one or two simpler missions.