This occurs during a side mission. After clearing all the mines from the city, you will have a tank battle again with Deathstroke. Note: You will not trigger the final three mine locations until the end of the main storyline. Unlike the first battle, you do not have to scan the main tank. Just continue to fire your main cannon. Also, all five Cobras do not need to be destroyed. Make sure the sidekicks do not get involved, as the Cobra tanks are harder to kill because they can only be destroyed by a critical hit from the rear, and require a very long time to target lock.