Got this last night.
On the third mission, I grabbed the Precision Rifle from the shack and went to the objective where they give you the mission. After the cutscene, I feel down the cliff, using armor, cloaked and kept in the bushes. A car approaches. I waited, your allies begin coming down and attack enemies to the right. I sniped two guys to my left by the car, then sniped three guys to my right that were distracted by allies.
I honestly didn't think it was going to work and actually almost restarted it. It felt like I had alerted them and had been seen.
All I have left now is Delta....yuck.