In Episode 8: Sovereign Land, when you climb out from underground up a ladder there will be a trailer park in front of you. You need to reach the orange tactical gear box at the far end without being seen by one of the guards.
Run around the left of the outside of the park and past two trailers, when you reach the rocks drop down into the back of the trailer park and go into the trailer where the objective marker is. On the right will be the orange tactical gear box, open it to unlock the achievement.