3 Dog Tags
Hudson's Pulse Rifle
Once you're back on your foot, head to the left and lift the panel. Jump to the tunnel afterward and follow the straightforward path until you reach the ramp leading to the default floor. The alien is right inside the next room so head to the right and enter the vent before the glass breaks. Exit through the end of the vent to reach a room with a dead marine. From there, make your way out through the sewers.
After exiting the door, look to the right to find a lever. This will disable the steam. Pull another lever down to open the next door. Here, you'll encounter the sound-sensitive aliens. When you alert them, stay perfectly still until they go away.
Continue along the sewers until you reach another lever. Pull it to activate the sewage pump. The noise will attract the nearby xenos and they'll detonate themselves. Proceed to the next sewage pump lever and carefully activate it to clear the room of xenos.
Cut the flashing hatch open and proceed to the next room. A couple of xenos are waiting below and you have to clear them out as well. Make you way to the lever on the other side of the walkway and pull it to activate the sewage pump again. Cut open the next door below. You'll find Oneal ahead. Follow the pipe to the left and continue until you reach another room with more of those blind xenos. You have no choice but to carefully and slowly get past them without alerting them.
Make your way upstairs and go through the tunnel. Cut open the blast door again and open the next door. The large xeno will appear again. Get past the first door and seal it. Cut the next door open and do the same for the next door. You'll find the elevator in the next room so quickly ride it and escape.
After regrouping with Oneal, get your gear back from the bag and exit through the next door. Before following Oneal, check the small room ahead to find this mission's legendary weapon: Hudson's Pulse Rifle
Continue following Oneal until you reach outside. Kill more xenos that will appear. However before moving forth, find a ramp leading to an overturned container van to the left to find a dog tag there.
Pick up the armor pieces nearby then proceed to the next area. Kill the xenos nearby and revive Reid. Kill more xenos that will jump unto you then regroup with her. Head back to the previous area and protect her as she tries to get the comm tower up. Continue defending your position until the comms are re-established. The large xeno will appear and chase the girls.
Once your objective is updated, continue forth and follow Oneal. Fight your way through a few more xenos until you reach a closed hatch ahead. Check the floor in front of that door to get the second dog tag of the mission.
Continue forth until you're able to enter one of the buildings. Go upstairs then jump down to the broken stairs. Grab the armor pieces to the left then cut the door open. Exit through the door but before you explore the area, check the floor behind the crate under the stairwell ahead. You should find the last dog tag of the mission there.
Proceed to the other side of the hangar to meet up with Bella and Reid. Take out more xenos lurking around, including one lurker. Oneal will disappear and you'll have to chase after him. Exit the hangar and drop down to the lower ground ahead. The giant xeno will make its appearance again. Quickly run to the pipe to your right to avoid getting killed.
Fight your way through more xenos and make your way to the left. Replenish your ammo then jump through the hole. Go to the left and crawl under the broken grate. Take out more xenos along the way. Regroup with your team inside the container van. Jump back to the ground and head for the gate. Wait for it to open then quickly make your way inside.
Operate the power loader to combat the giant xeno. Keep minimum distance and hit it with the power loader's melee attacks. Don't mind the smaller xenos; just keep your eyes on the giant xeno until you successfully take it down.