So far I only tried to use armored trains as sort of a strategic reserve, - most of the time they are concentrated under direct army command, with an occasional rush or two to reinforce some other far-away stack in need of assistance. Every time I tried them alone against weak enemy garrisons they got slaughtered.
But I have a feeling that I'm missing something. I mean, it's the most mobile unit in game - there should be a potential for daring raids and rapid breakthroughs, I just can't figure the right way to do it.
So, how do you employ your armored trains?
Also, does "armored support" ability give the bonus to the elements of the same division only or to the whole stack?