If the defender is eliminated, victorious attacking units may advance after combat into the hex. Provided at least one attacking unit was armour, any other armour unit which did not attack, but which was adjacent to an attacking unit, may now be placed on the newly gained hex (the "breakthrough hex"). These armoured units may then "exploit", i.e. move again, provided they keep to a chain with no more than one empty hex between each unit, and then attack - a key tactic in surrounding enemy units. There is no limit to the number of armour units which may stack on or attack from the original breakthrough hex, provided the overstack is rectified by the end of the turn. Breakthrough against an empty enemy-controlled hex is not allowed, but a key position can be attacked by obtaining an overstacked armoured breakthrough against a weakly held hex adjacent to it.