Man, I don’t remember ever coming across this.
I scoured the rulebooks but couldn’t find, also the FAQs
You can ignore subs/transports in combat movement phase.
It appears to me that you don’t have to say whether you’re actually attacking the sub(s) until you decide to roll that battle, that sea zone. (So you never need to declare ahead of time, just decide when you get to that sea zone)
Is this correct? Surely I missed something somewhere.
Triple A (which we never trust, like P@nther has in his signature) makes you say whether you are attacking transports/subs before any dice are rolled.