11 Nov 2014
I personally found chips dubbo on the level "The Pillar Of Autumn" and unlocked this achievement after killing the enemies that come out of the pod when you first encounter the Covenant boarding your ship. I kept all my marines alive at this section and when I walked around the corner I unlocked it.
If you have any other places you unlocked this achievement then please let me know and I'll add it to the guide! :)