In the "Ground Zeroes" mission, rescued the prisoner to be executed and extracted him via chopper

Within the main mission, Ground Zeroes, there will be a specific prisoner you must rescue and extract before they are executed by a group of enemy soldiers. As soon as the mission starts, make your way down the hill, past the spotlight and locked fence. You will now want to enter the first camp directly to your left; it has several white tents set up.

Once you get inside this area, either sneak by the guards or take them out - it's entirely up to you. Now head to the northwest end of this camp, past the tents, and you will come across a small wooden shack with some crates. The prisoner is sitting here with a bag over their head.

All you have to do now is pick them up and extract them via the helicopter. To do this, call in the extraction helicopter by pressing the start button and choose the landing zone that is located where the mission's starting point is located. Run back up the hill with the prisoner and as soon as they're safely inside the helicopter, the achievement will unlock.