I think you're really close with that. Notice the tick box for "Is tactical group"? You can set a group up that only spawns when the player sub comes into a "trigger" area. I usually use a MapZone for that, and then Triggers and Events. The ControlZone might be a short-cut of sorts for that, but of course, like most things Ubisoft did, there is no documentation, and a person has to do 3 weeks of test missions just to find one little tidbit of info they might never use otherwise...