You’ve cleared out the Covenant forces in the courtyard of the base, reactivated a nearby AA gun, and reestablished contact between Sword Base and command, but now the real task begins. The Covenant have breached the base, and you’ll have to rush back, clear a path to the roof, and deal with the Covenant Corvette hovering overhead before you finish the Halo: Reach "ONI Sword Base" mission.
“Minimum Safe Distance”
Once you’ve reactivated the AA gun and the relay at Farragut Outpost, you’ll get an urgent transmission ordering you back to Sword Base. Hop in a Warthog and race back quickly.
When you approach the front gate, the place is under siege. Covenant vehicles and turrets have been deployed near the entrance. You can take the time to eliminate the attackers or just rush past them to the door switch and inside.
The health pack and ammo are right were you left them when you first went outside, so quickly heal up and rearm before the Covenant descend on you from the top of the ramp.
Once the attack begins, use the concrete dividers as cover and try to eliminate the Jackals, Grunts, and Elites with headshots. If you hit them as they move into position you can take out quite a few before they mount a counterattack.
Fight your way past the Elites to the main courtyard, where the base entrance is now open.
The Hunters Become the Hunted
Down the ramp into the base, you’ll meet up with some marines struggling to take out a pair of Hunters. These are among the toughest enemies in the game, and to deal with them you’ll have to shoot the fleshy orange parts not covered by their armor. You can let the marines distract them and snipe their backs from afar, or charge right in, dodge their advance, and shotgun them in the back.
Grenades are handy, too, but it takes a few to kill a Hunter. However you deal with them, just keep moving and avoid their plasma blasts. Remember that “Armor Lock” grants you temporary invulnerability at the expense of mobility.
Once they’re down, take out the Elite guarding the elevator at the back of the room, then take it to the base’s interior.
“Office of Naval Intelligence”
As the elevator opens, you enter a room with an Assault Rifle, some armor abilities, and a couple health packs. Move quickly, because Covenant will attack from the end of the long hallway.
Take out the Grunts and their Elite commander, then round the corner to the right. A door will open onto a firefight between a Covenant squad and Jorge and his men. Assist them in taking out the bad guys, then follow Jorge and the rest of Noble Team up through the offices. Keep heading upstairs, taking out the Grunts, Jackals, and Elites you come across along the way.
Eventually, you’ll reach the top floor and take out an Elite Zealot wielding a Concussion Rifle. A transmission from command urges you to accelerate your pace. Take a right and you’ll enter a corridor blasted open by the Covenant Corvette above. Clear out the Covenant in the area (watch for cloaked Elites), then pick up one of the Rocket Launchers near the hole in the roof.
Once the immediate area is clear, use your Rocket Launcher to take out the Phantom and any remaining Banshees outside. Once they’re clear, USNC Longswords will move in and force the Corvette out of position. Once it’s clear, an Orbital Platform takes it out.
Congratulations, the base is saved. You’ve finished the Halo: Reach "ONI Sword Base" mission.
Unfortunately, the fight for Reach is far from over.