Turn around to find the Declassify Skull. In this section, you have to dig in and survive the enemy attack waves. In addition to the normal waves, Nemacysts will join the waves.
Before the mission starts, you can collect the COG tag in front of the statue in the middle fountain.
Deploy the two auto-turrets one in front of each flight of stairs. Take note that you have to also reload them from time to time. There will be two waves of enemy attacks you should survive. Just stay in your position and keep an eye on the stairs since enemies will be rushing your position using any of the two stairs.
The second wave will most likely contain heavy enemies such as Boomers and Maulers. When dealing with Maulers, keep your distance and attack their foot when their shields are up. For Boomers, you can simply take cover and attack them from behind cover.