F.E.A.R. Files

Simple, like it says, just get to this point in the campaign. The difficulty doesn't matter. The achievement just pop when the credits start to roll over the screen.

This campaign focuses more on the combat ant shooting than the Extraction Point campaign so you should have an easy time completing the other one if you haven't done already.

Here is a great walkthrough if you get stuck:
http://www.gamefaqs.com/computer/doswin/file/941968/51786