To get this achievement you have to complete the final mission of the 2nd chapter. The mission is the 7th mission in the chapter and is callled Douaumont Fort.
This is part of the normal story progression, hence the achievement is not missable!
If you need help at any point of the level you can refer to this video:
This video is not mine all credit goes to YOGSCAST Kim
Hope this helps you guys ;-)
Anything wrong with the solution? Let me know in the comments :-)