You will unlock this achievement upon completion of the first mission after jump training. This mission is pretty easy, as it gives you a feel for the game controls and how to play.
The first part of this mission has three objectives. You need to destroy the hill houses AA gun, destroy the northeast gate AA gun, and destroy the town hall AA guns. These can be completed in any order. After the first part of the mission is done you move on to assemble with Airborne at the north gate. From here you are directed to locate the missing sniper team, which you discover is pinned down by a German commander. Eliminate him and make your way back to te town square where you meet up with Airborne. From here, the last part of the missin begins, you need to elimnate the German officers scattered throughout the town hall. This mission should take any where from 20 minutes to 35 minutes to complete depending on the difficulty you are playing on.
I hope this solution helped! Leave a comment letting me know if there is any room for improvement! Thanks.