1. Continue along the mission until you reach the part where you have to restore power to the lift and use it to reach the upper floor. Get off the lift and continue along the hallway again until you reach the maker remains. Kill the xenos along the way; as usual, be careful of the camouflaged lurkers on the walls and ceilings. Follow the walkway, past the tent to the left and two cocooned scientists. Before moving forth, check the box in the corner of the catwalk past the second scientist to get the mission's first dog tag.
2. Once you've reached the second AA gun emplacement, check the ground near the forklift and your allies to find another dog tag.
3. Head where the allied dropship crashed. Fight through more xeno ambushes and go through the wreckage. Once exit the wreckage, you'll find your downed allies. Check the ground beside them to find the last dog tag in the mission.