I tested it too, big combo battle with subs on both sides, air on both sides, destroyers only on one side. It was a pretty complicated affair.
But it is a lot more like playing the game on a board. You count up hits and assign casualties at the time they’re supposed to be assigned.
Too bad Triple A isn’t set up this way automatically, and too bad it doesn’t conveniently keep the tally of hits that must be assigned to ships, or must not be assigned to subs, BUT
In many scenarios this will be the best way to go.
Summary:
Roll mixed fleet battles in Edit mode.
Click through (don’t assign any hits) premature casualty choice prompts (subs hit and don’t have surprise strike because of enemy destroyers, or planes hit without accompanying destroyers)
until you’re at the place where casualties need to be assigned.
You need to count up the hits and assign them legally. Since you’re in edit mode you don’t have to, as you don’t have a computerized check on you here.
Assign sub hits to ships only. Assign plane hits to non-subs only, when there is no friendly destroyer to the planes present.
This is the way to keep all dice and everything inside Triple A without editing units off the board. It keeps the battle in the history.
But you ARE in edit mode, so human error can happen.