In my last game, I had well over 400 units... 150 mech infantry, 100 modern armour, some 100 swordsmen

, and planes n' ships... This has not happened to me yet!
But i've seen some wild battles! Ie. losing ten modern armour on GRASSLAND against infantry when i attack, but the AI regular tanks had no problem beating the same infantry on the next turn!
Doubling the HP is the way to go!