Extracting three APCs
You can deal with this task when completing the mission for the first time, but you of course need to have CARGO 2 (transporting heavy objects) to complete this hidden objective.
Enemy armored vehicles are not located in one specific point on the map, because all three APCs constantly travel around it. If you have proper equipment, you can place some big obstacle on the road, wait until an enemy vehicle stops before it and Fulton it. Optionally, you can wait until the soldier parks the vehicle in one of the guard places. An advantage of this method is that you don't have to rely on obstacles, but a disadvantage is that you can be seen by enemy soldiers.