Now that is simple.
- Choose DSRV as loadout in mission editor.
- Target must be sub and it must be different side, not sure about alliances. Different side, peace time works.
- You must be under 3 kts, then you use popup menu on nav map, same as spec ops.
DSRV should launch, and as it can't read target depth (it reads zero) it surfaces, slows down to 3kts on surface, starts to cavitate as hell. Anyway it still tries to get toward the target.
It needs new sensor reporting depth, totally new script, and some testing and thinking about the side trouble.