Good night sweet princeG 40

To unlock this achievement you simply let one of your buddies die during any of the subverted mission from a mortal wound. This usually happens when your buddy is insured to the point that he is laying on the ground and drops a blue smoke signal for you to find them. Once you locate him you will try to revive him with your shots. You will attempt to administer three shots to revive your buddy. After the third shot he will die.