This is nearly impossible on Elite. Start free play and set difficulty to Rookie. Be really cautious and keep in mind that you can't save in free play. If you did beat the campaign on Elite before, you should delete your save game. Create a new one or start a new one on a memory card and enter the mission via free play as the achievement is currently glitched. You can pick up as many Health Kits as you want, just don't use them. Starting a new game on rookie with an existing save game DOES NOT unlock the achievement.