You're without a weapon at the start of this chapter, so your first task is getting your hands on one. A couple of armed soldiers will approach the vent up ahead, so sprint to the vent, crouch behind it and wait for them to get close. When the first soldier comes to a halt, immediately move in and press the B/Circle button to take him as a human shield. You're automatically given a pistol when you take a shield, so headshot the second soldier and then press the B/Circle button to execute your shield.
Both soldiers were carrying Buqiang 800 rifles, so pick up both guns for extra ammo. Once you have the rifle, sprint up the steps and take cover behind the AC unit on the platform. The distance marker on screen is pointing to a sniper, so crouch behind cover, take aim with your rifle and shoot the sniper in the head to put him down.
Getting a weapon
With the sniper down, you still have several armed guards to contend with. Keep behind cover and pick off any guards you can see before moving up. Be careful when switching cover, as you may inadvertently be placing yourself in an enemy's line of fire. Always ensure the surrounding units are clear before switching cover.
There are three or four soldiers by the door at the other end of the rooftop, so pick them off with your rifle before moving out into the open. Scour the platform for weapons and ammo before opening the door at the far end of the rooftop to enter the building. Be sure to pick up the two Buqiang 800 rifles dropped by the soldiers as well before heading inside.
Proceed down the stairs beyond the door. Take the guard on the walkway hostage and execute him. Then, head down the ramp to your left and take cover behind one of the machines there. A ton of guards will appear on the walkway at the other end of the area. Gun down the guards on the parallel walkway and keep an eye on the machines to your right, as a few of the guards may move there to get a better shot at you.
Once you've dealt with the guards in sight, move to the right and take cover by the stairs on the other side of the walkway. Pick off any soldiers on the upper walkway and further down before moving out from cover. The game will auto-save once you've killed the last enemy in this area.
Use the Buqiang 800 rifle to pick off distant enemies.
You can find a fire extinguisher on the upper walkway in this area before moving on. As well, press down on the D-pad and pick up any Buqiang 800 rifles that appear for extra ammo. When ready, follow the walkway into the next area and keep an eye on your left for some stairs. Head up the stairs and take cover behind the machine at the far end of the upper walkway. Throw and shoot the fire extinguisher if you brought it and then start picking off the soldiers below with your rifle.
When the area below is clear, head down the steps at the end of the upper walkway and enter the corridor straight ahead. Follow this corridor to its end and enter the elevator there to move on to the next area.
After the cutscene, move to the end of the hall and turn right. Move through the doorway here and take cover behind the desk just beyond it. Take out the two guards by the windows and then take cover behind one of the display cases to your left. Kill any remaining guards on this side of the room and the army will enter from the other side. Take cover behind one of the display cases at this point and start putting down the soldiers with your rifle.
There will be a gunship hovering outside. Ignore this gunship and try your best to avoid taking fire from it. You'll have to shoot it down eventually, but this is best done with a machine gun, which you can only acquire in the next room. It's easy enough to avoid the gunship here; just remain by the display cases and stay away from the windows.
The game will auto-save when you kill the last soldier in this room, so don't move on to the next area until you've done that. Once you're ready to move on, head through the opening at the other end of the room and take cover behind the tiled wall. There's a machine gunner at the other end of this area. There will be a distance marker pointing at him. You must dispatch this enemy so you can pick up his machine gun and use it to shoot down the gunship hovering outside.
You'll need a machine gun to shoot down the gunship hovering outside.
If you still have a rifle, you should be able to take out all of the soldiers, including the machine gunner, from behind the tiled wall. If you're out of rifle ammo or need to get closer, move up to the pillar on the left once you've killed as many of the soldiers as you can from your current position.
When the room seems to be clear of soldiers, move up to the cubicle wall beyond the pillar. From here, move over to the cubicle wall by the windows on the far right. The gunship outside will hover back and forth between this room and the adjacent one, so wait until the gunship flies out of sight and then make a mad dash for the machine gun at the other end of the room. Press down on the D-pad to locate the weapon if need be.
Once you have the machine gun, your next task is to eliminate the second machine gunner in the adjacent room, otherwise he'll give you a hard time as you're trying to shoot down the gunship. This enemy is covering by the pillar straight across from the doorway, so just approach the doorway and quickly headshot him when he pops out from cover to fire.
With the second machine gunner down, fallback and take cover at the corner of the desk by the windows. From here you can blindfire at the gunship when it reappears while taking little damage. To blindfire, press RT/R1 while behind cover without holding LT/L1. Continuously blindfire at the gunship, keeping your target reticule trained on it while it's in view, and it'll go down in no time.
Taking down the gunship
Once you've managed to destroy the gunship, return to the doorway into the adjacent room. Take cover next to the doorway and pick off any enemies you can see in this room. Move in and dispatch any remaining enemies, then pick up the machine gun on the floor and pry open the double-door at the other end of the room to move on.
Through the door, immediately take cover behind one of the display cases up ahead and begin picking off the soldiers in this room. You can move up to the pillar next to the wall on the left once you've thinned their ranks a bit. There are two guards armed with rifles behind the counter at the other end of the room, so be careful.
When the room is clear, pick up the two rifles dropped by the guards behind the counter and then proceed through the nearby doorway. Enter the smoke-filled stairwell at the other end of the hall and keep sprinting until you come to a kitchen.
Kick down the two doors in the kitchen area and immediately take cover behind the counter in the next room. A ton of soldiers will pile out of the crashed helicopter here; equip your machine gun and keep firing at the helicopter door as they come out. You'll kill the majority of them if you were quick enough. Once you've done that, look for a fire extinguisher behind the counter you're covering behind. Throw the extinguisher toward any remaining soldiers and shoot it to dispatch them.
When the first floor is clear, vault over the cover in front of the crashed helicopter and head up the ruined stairs to reach the upper walkway. Take cover behind one of the tables along the walkway, as some more enemies will soon appear. Blindfire at any enemies that try to rush your cover and then use your rifle to pick off the enemies covering in front of the windows on the other side of the walkway.
Dealing with the reinforcements
Scour the area for weapons and ammo before moving through the doorway on the upper walkway. Head up the stairs beyond the doorway to reach the executive floor. Kick in the double-door you come to and then kick down the door in the next room. Take cover behind one of the overturned couches in this room and shred the incoming soldiers with your machine gun. Clean up with your rifle and then push through the open door at the other end.
Take cover behind the stuffed zebra along the corridor and use your machine gun or assault rifle to waste the enemies that appear at the other end. Once you've dealt with those enemies, move into the next room and take cover. It's best to take cover behind one of the stuffed leopard displays on the left or right, as taking cover anywhere in the middle will likely put you in at least one enemy's line of fire.
Defeat the enemies in this room and then kick down the double-door at the other end. Move into the office here to trigger a cutscene and complete the chapter.