Just a Box Achievement
Just a Box10
While in Guerrilla mode, complete an infiltration sequence without being detected
Just spawn, and immediately crouch (using ). Stay crouched the entire wave. Just move through the map and eliminate all 5 enemies without setting off any detections. Follow the video for any additional level details.
Once you eliminate the 5 enemies and the mission ends, you will get the achievement.
Thanks to Maka for the great description and video.