Disable Anti-Aircraft Turret
In order to shut down the AA turret, you'll need to make your way through the bunker and reach the control room for the installation. Begin by maneuvering through the hallways near your start point (there are two, but they both lead to the same room), but be careful of the two SBD's that'll attempt to impede your path. When they're both dead, move into the large room where the halls meet up and place explosives on the piping near the wall. Detonating this will let you through the nearby door, but be sure all of your squadmates are fully healed before you blow it.

Locate Turret Controls

These windows will need to be quickly closed if you don't want to have to deal with an infinite number of Geonosian enemies.

When the door's open, quickly shuffle your squaddies into the room beyond and instruct one of them to slice the console by the window. The Geonosians, apparently having been too dumb to take up guard positions inside the bunker itself, have to resort to smashing the window open and flying through; slicing the terminal will close the blast shields, preventing them from accessing the interior and giving you a nice squishy feeling, as well.

At the top of the nearby ramp, you'll have to take down two more SBD's, so whip out your EC grenades and put them into service. Beyond the next door is a room with not one, but two separate windows that you'll need to slice, so charge in and quickly task two of your squaddies to slicing. If you wait too long, an Elite will fly up outside one of the windows and start blasting, so get your squadmates into position and cover their backs until the blast shields close. Even if they take a bit of damage, you'll have a bacta dispenser at your disposal to heal them with after you're in the clear.

When you proceed out the doorway here, you'll come to the upper level of the room you blew up before; it appears that the turret controls are still kicking, so you'll need to place another charge on the platform here to finally destroy the place once and for all. Before you do so, though, take out the SBD and the battle droids on the ground below, then heal your team up completely.

Video Walk-through

You'l l need to defeat these SBD's quickly if you want to get to the window shutters.

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Exit Bunker
When you blow the last charge, the doorway near the turret controls will automatically open, revealing a squad of battle droids and a pair of SBD's. There are more battle droids behind the SBD's that'll attempt to open the two windows in the room so that the Geonosians can enter. You can't really hope to stop these guys (at least, not without getting killed by the SBD's, which is a bad thing), but you'll still want to enter the room speedily and start hacking the window consoles. The best bet here is to throw two or three EC detonators at the SBD's, finish them off with blaster fire, then charge into the room like you did previously, tasking two soldiers to slice and fending off the Geonosians with the remaining soldier. Again, there'll be another Elite outside one of the windows, so move quickly before it can blast you all to pieces.

Now that you have the bunker neutralized, all that's left is your exfiltration. There'll be three more SBD's in the hallways leading to the exit from the facility, but you shouldn't need to do anything too special to terminate them. Remember that you have a bacta dispenser in the last window room, so try to let your squadmates do most of the damage to prevent you from expending too much of your grenade ammo.

Territory

Advance to Coreship
You know the drill by now; set your squaddie in the sniping position near the start of this level, place the other two in position nearby, then start running ahead to trigger the spawning of bugs. When the dust has settled, you'll be able to heal up with the bacta dispenser nearby and refill your ammo, as well.

As you proceed down the canyon, you'll come to another sniping spot that looks out over a chasm, on the other side of which is a squad of battle droids. Let Sev do his thing at the spot while you and your team deal with any Geonosians that pop up from the chasm itself--these guys are in every nook and cranny on the planet, it seems.

Around the bend from that little melee, you'll come to another crashed dropship. When you advance close enough to it, you'll find that the turret on its side is usable, so quickly send a trooper into it, and another one to the snipe spot nearby; they'll be able to handily disable all of the SBD's and battle droids that are coming your way. As per usual, you should run forward a bit to lure any more SBD's back into the turret's line of fire before disengaging your troopers and moving on.