Attack/defence order when equal stat?

Is there a rule I couldnt find written anywhere stating what unit attack/defend first when u have different units with same stat in a stack?
ex: militia or tank defends first? Submarine or marine attack first? Even trickier u have a stack in DS wih militias infs and helis?? Which one dfend 1sr2nd and 3rd?
cheers

Is random.

Ivan say it.

(can't bring the quote here now)

Well i know the one with more critical hit chance attack first. with the same stat.

I think it's like this for attack: other -> main attack -> secondary attack -> main def -> secondary def
(rjust change attack for defense and vice versa if defending)

and it's sorted by the highest stat (att/def, then highest HP and highest crit

First unit to attack -> more attack -> more critical hit.
first unit to defend are -> more defence-> more critical chacne