This is a story related achievement. You will unlock this when you complete the mission at the Karlshorst Command Center (Chapter 7).
After you kill the higher ranked officer in the underground barracks, you exit through the way you came in. You need to kill all the Russian Snipers. There will be 6 in elevated positions. There will also be 4 snipers that are mobile and will chase you around the destroyed city. Once you kill the final Russian sniper, which is located in the big tower off in the distance, you will complete the mission.