Some wounds never heal – This is awarded upon the completion of the level Project NOYA. You have to play some of the previous campaign missions before you will be able to play this one. You can play this mission on any difficulty and still be able to unlock it. This mission is about the same length as all the other ones and should take you a maximum of 30-40 minutes to complete if on the easier difficulties. If you get stuck then you can use this video from NextGenTactics and he will guide you through.
Normal Guide
Veteran Guide