A feature that would be nice at some point; but not urgently needed. estimated didfficulty to code: moderate
Breakthrough woudl be a unit ability that should only be taken by units that also have blitz. (though units with blitz need not have breakthrough)
If you attack an enemy territory with a number of units greater than the number of defenders; units with breakthrough can move on to other territories before you get to the combat phase.
Example: you attack with 6 units; defender has 4 units. you have 3 units with breakthrough; 6-4=2, so 2 of your units with breakthrough could move past that territory to a deeper one; this is during the combat move phase.
The intent of this feature is to allow maps wherein one inf can't stop massive tank and other mobile armies blitz armies just by forcing a battle with one guy. This would not change any existing maps since none of those units would have the breakthrough ability; but future maps might incorporate it.