As the description says you have to complete Act 2 Chapter 7 (Standard or Arcade) on any difficulty, I got mine on Normal.
You will start this chapter on board of a Gas Barge right after you pick up Dizzy Wallin. The mission is to eliminate any incoming enemy Gas Barges. You’ll do so by grabbing one of the Turrets, (some kind of Boomshot Cannons), just get close to it and by pressing X, you will be able to operate it. Try to aim a little bit higher than you normally do to hit your target. Since the enemies will pop from different angles, try to switch between Turrets to have a better clean shot. After you kill them you’ll have a cut scene and the next objective will be to survive the Tempest attack, which consists of killing a gigantic Insect. You can easily kill it with your Lancer or Hammerburst assault rifle. Point it to his head to get a better result. As soon as you kill it your achievement will be unlocked.
I think this chapter was fun and fair, I’m sure you will not have trouble getting the achievement.
Best of luck.