Cut the chains of the gate open and proceed to the entrance under the bridge. Once you've reached Elliott's computer room, you can find the Declassify Mission Skull there. Activating it will allow locusts to use one-shots. While the bot is hacking the mainframe, you have to fend off a heavy enemy attack waves and prevent them from reaching the bot. Grab and deploy the nearby gnasher sentinel to protect the entrance leading to the computer room.
If you have the declassify mission active, the Oneshot-wielding locusts will always try to set up in the balcony far ahead. You can encircle them using the corridors to the left or right though you have to go back immediately since the enemies will still target the bot.
There's a COG tag in the balcony on the other side. Check the corner upstairs, above the COG skull in the first floor. This is the same balcony where the Oneshot locusts camp and take their potshots.
After defeating the first wave, the bot will move out in the open and attempt to hack the main terminal. Grab the auto-turret and deploy it near the bot's location to protect it. Before the second enemy wave comes in, you may want to grab some ammo and plant some grenades along the stairs to help you deal with the rushing enemies.
After taking out more enemies, a berserker will appear. Along with some flamers. Take out the flamers first and other minor soldiers so you can grab the Flamethrower later on. Replace one of your weapons with the flamethrower and scorch the berseker. Once it is burned, keep firing at it using your other weapon to deal damage. Once it cools down and returns to its iron-skin state, burn it again with the flamethrower and repeat the process. The mission will be complete afterward.
This is how I killed them on hardcore. (I'm not sure but I don't think the flame sentinel appears on hardcore, so had to rely on gnasher sentinel).
1. Before the berserker wave starts, quickly place your gnasher sentinel near your bot.
2. Run to the balcony at the other end of the room so that you are behind the berserkers and scorcher-carrying scouts as they enter the room.
3. Take out the scouts by shooting their flame packs to make them explode. (Note, they're sometimes armoured so shooting anywhere else takes time and wastes ammo).
4. Grab the dropped scorchers and run back to your sentinel and bot. Don't bother attacking the berserkers here, you'll probably run out of scorcher.
5. As the berserkers approach the bot *make sure they are within shooting range of the gnasher sentinel*. Light them up with the scorcher - just enough to make them vulnerable and no more. You need to save scorcher ammo. The sentinel will deal huge damage.
6. Repeat.
Anyone having problems with the above comments, this is for you. When you walk into the main room, to the right you will see a carpeted area with statues of heads. One of these statues has glowing eyes. If you walk up to this statue it will prompt you to push 'X' this will open a door and inside are a few extra useful items including a auto-turret and an onyx ammo box save this for the end. If you run out of flamethrower bullets use this box and it will give you significant ammo. Hope this helps
I'm having the same problem. Been on this level for weeks :(. I've been given no scorcher on this level and when I do I exaust it on the berserkers without even killing one.I've tried all the advice given on this website. Wish someone will give me advice that will help me pass this level because I'd like to move on.
Okay, so what do I do after I run out of flamethrowe ammo, and there are no more flamethrowers around, and I have two very angry berserkers who are immune to basically all types of ammo running around tearing the COG apart? Might have to load last checkpoint :(