Complete a mission without dying or loading a checkpoint.Pathfinder on Recruit again, is the easiest mission to do this on. Take your time and try not to get shot if possible. If you start to take a lot of damage, look around for Med Kits and other health recovery items. The enemies you kill will usually drop a med kit, which should heal you for 25 health. Let your teammates lead to reduce the risk of dying even more. If play through carefully, you can easily nab this and the Pea Shooter achievement.