There are a total of 4 machine gun turrets located on either side of the path you follow in this mission that you must use to get at least one Wraith kill with each turret. You'll want to start the mission off by hopping on the first gun and waiting for the Wraith to come down from the top of the screen. Then rush up to the first turret on the right to take out at least one more Wraith before moving straight across the path to the turret on the left for another Wraith kill. The last turret is to the top left of the area, and you will hopefully have at least one of the five Wraith targets left. The achievement will pop when you finish the mission.