Instructions
Follow the dirt road to the bunker at the end of Chapter Eight.
Clear the bunker of enemies and walk past the barrels and boxes to find the mortar. Press "A" to take control of it. There will now be a number of enemies ahead, blocking the road.
Press the left analog stick to move the Y-axis of the mortar's aim, and press the right analog stick to adjust its X-axis. Aim low and to the left to take out both the fence and the truck.
Pull up on the left stick and aim right with the right stick to target the trucks on the other side.
Move the aim to take out the remaining soldiers. Keep firing shells to see where they land and adjust the aim accordingly. Once you've taken out all the enemies, the mission will end.