#1. After opening a closed hatch using a powerloader, check the body on an open container to the left to find the mission's first dog tag.
#2. After regrouping with Bella, cut the next door open and follow Oneal to the right. Follow the trail of blood on the floor and turn to the right again. Near the broken window lies another dog tag.
#3: After fighting your way through the storage vats/ tanks, you'll finally reach a control room or some sort. This dog tag is located on top of a console in the upper left door. Refer to the video below for more details.