You have the choice of playing as China or NATO for the final mission. There is an achievement for each so this trick will greatly help for both.
The AI in this game gets a massive handicap if they are not on screen. So much that if you stare at the ground the damage you take is roughly 1/50th. You will instantly become the most absorbent bullet sponge with out using cheats. Use this "tactic" anytime you are outside on the final mission.
Once you get inside the two bunkers, use the grenade launcher around corners. You must clear the area around the switches so you don't get killed in the process.
After you activate the two switches, start using that "tactic" towards the large tower. The rest of the mission is very easy and forgettable (I stopped playing this game 3 years ago).
Staring at the ground is the best advice for this achievement.