In order to unlock this achievement you are going to have to complete the sixth campaign mission on the guerilla difficulty setting. This isn't too hard to get done, as I found it to be the easiest mission to complete on this difficulty.
Some pointers to help you through, always stay on top of the rockets being shot at your helicopter. Don't worry too much about the trucks, just do your best to locate all of the enemies and take them out as quickly as you can. Also, make good use of the counter measures, you can shoot out flares by pressing the A button that will deter any incoming missile. At the very end of the level you will have to defend the trucks on the bridge while they plant explosives. Just stay on top of the enemies getting on the bridge via the on ramp, if you have to, get a little closer to them to get better shots.
Video credit goes to Siberian Gaming.I hope this solution helped! Leave a comment letting me know if there is any room for improvement! Thanks.