Objective: Sabotage the remote airbase with your silenced weapons and heartbeat sensor.
Advice: Work together as a team. For the first building you don't even need to shoot the two passing guards. Once they pass, simply crawl in, knife the guard sitting in the chair looking depressed, then turn around and knife the enemy by the objective. Once activated, get out, and move on. Use the same strategy you used on the two sniping levels to complete this one. Take your time and if your going to shoot the enemies take them out in pairs and watch for stragglers. Fairly easy if you be patient and use your heartbeat sensor.