#1. After clearing the first escape pod bay, continue past the locker room and head to the next bay. Kill more PMCs here. There's another dog tag in the area. Proceed to the main hall then turn right to the first corridor then right again. You should find the dog tag on top of a metal crate.
#2. After going through the submerged maintenance ducts, you'll find a stairwell. It will collapse as you go along. Jump on the debris then look to the left to find some pick-ups and the dog tag.
#3. Near the end of the mission, you'll have to take a lift to reach the drop ship. After disembarking, don't leave the area yet. Check the floor behind the large container to your left to find the mission's last dog tag.