Last Line of Defense is mission 04A in Ace Combat X: Skies of Deception.
Leasath's Miller Unit it meeting up at Kinghill. Based on the sheer strength of the enemy force, an offensive aimed at retaking Port Patterson appears imminent. A partially completed highway runs directly from Kingshill straight into the heart of the Port Patterson. The enemy intends to use this highway to swiftly spearhead its way through Aurelian defense. Their ground forces must be destroyed if Port Patterson is to remain Aurelian. Aurelian forces are in a precarious position. On the highway leading to Port Patterson, there is a tunnel. If an enemy tank makes it to the tunnel, it will be beyond the reach of any air assault. If even one enemy tank enters the tunnel, mission will fail.