After destroying or capturing the T-72U Tank, you have to find another way in, which means going back and destroying a wall that blocks your path at the prison camp.
Go back up the stairs you went down, but if you want rations, they are under the stairs. When you get up there, there is 1 guard right there, so take him out silently. You can take either ladder down, but watch out for the guards on each side, I suggest shooting them in the head with the Mk22 before going down, and then exit the building.
When you go outside, there will only be one guy on the catwalk and that is strait in front of you, so either tranq him or ignore him when you go by. There is no sniper in the tower, so keep going. There will be 1 guy when you look down the path, so tranq him as well. Going past him, there will be another guy, but this guy will be guarding the exit, so wall press and knock to get his attention. When he comes around, that's your time to go, but don't head south, there will be a way to the west that you can go through.
Then you get to the area to where you get to blow up the wall. Make sure you are not caught when going around the houses, the wall should be on the top, west corner, but not up the road. I recommend tranqing everyone so no one hears the blast. Just enter after and that ends the mission.
There are, but none found yet
EDIT: Found it. Backtrack all the way south to the Camino de Lava:Hillside area. Find one POW at the far end of the area from where you enter. It was a Rank C Intel POW for me.
S Rank Run:Edit
Your Sneaking Suit makes works of wonders, so I recommend wearing one. All you do is hold up everyone in your way and if there is someone off the distance, then shoot him with the Mosin Nagant to get a one shot sleep if it's leveled up high. At the camp, just hold up everyone, put C4 on the wall, boom, your in.
A time of 4:45 will be plenty fast for an S rank.