The level spawns you in a modified Quarry map, where you are tasked to kill Parg Vol. Choose a loadout with a decent ranged weapon so you can snipe the enemies from a safe distance.
The closest group of Covies are 4 Grunts led by 2 Elites. Begin by popping all the grunts, then move to the Elites, using the big rock to the side for cover. Follow up by eliminating any Jackals or Grunts that are harassing you, then move down into the valley. Once you get close the big UNSC box directly in front of you, Dalton will send you 2 Sniper Rilfes and a Railgun. At the same time, however, 5 or 6 Jackal snipers and an Elite manning a plasma turret will have you in their sights. Stay behind the big box and snipe all the foes up on the rocky outcropping before moving on.
After all foes not on the plateau are dead, grab the Railgun and move up the slope to reach the Phantom, which will take off when you get to close. When the Phantom starts to take off, immediately turn and run all the way back to the UNSC ammo boxes, because a very large force will assault you soon and this is a much better position to anticipate them.
The Covies from the drop pods consist of about 5 or so Elites, at least 2 of them being Fuel Rod Cannon wielding Warriors and the rest Majors. They are supported by 3 or so Jackals and 5 Grunts. Use any remaining sniper ammo for any targets you see (takes 3 shots to kill a Warrior and 2 shots for a Major), then switch to the Railgun for any Elites left, which can kill any rank in a single shot. Although the Railgun has no scope, if you click the "zoom in" button while it is charging you can use your binoculars as an effective scope anyway.
Once all foes are dead, feel free to go to the top of the plateau if you want to use Covenant weapons. If not, refill your Railgun and move on. Up ahead are 2 lookout towers that are manned by a garrison of 2 Elites (1 Warrior 1 Major) and 4 Grunts. Stay near some rocks or boxes for cover, since they carry ranged weapons, and hit them with a Rail shot to deal with them.
Clearing out the remaining foes, you'll find down in the next area Parg Vol's expansive UNSC collection, guarding by another big garrison. If you have the patience to run all the way back to the old ammo crates back in the first area, you'll have enough Railgun ammo to take out most of the Elites from a distance before they even see you. Focus on the nearest lookout tower first, popping the little Covies and a Jackal Sniper before getting the Major with a Rail shot. From there, look out over the cliff edge where you can see 2 Elites and a Grunt near one of the Scorpion tanks. Take them out, then drop down to the lower area and you can refill all your ammo at the stockpile. Feel free to grab any weapons of your choice and you use them on the Elite Warrior with the Fuel Rod cannon and the Minor near the next lookout tower. After that, only little guys remain.
When the last Grunt is killed, refill your weapons (and swap for a Regen Field or Autosentry if you want one) and board the nearest tank. Get the tank out of the pit area fast, before the Phantoms bring in a whole party of foes. Head straight for the second lookout tower and move past it, going to a small area shaded by cliffs that looks like a dead end. This is the best place to start the fight with, since it forces foes to come to you. Take a few shots at the Phantoms as they drop their loads, and then aim at the ground forces. Take out the pair of Wraiths first with 2 shots each, and then the Elites, moving back to the "Defend" marker and taking out anything that you can. When the remaining targets conceal themselves in the metal structures or mass up on the cliff behind them, ease the tank further back to the dead end and exit the tank. It's much quicker to take them out manually, but don't stray too far form the tank, because when you clear this wave 2 drop pods will send another set of foes almost on top of the "Defend" marker. Make sure your tank isn't right there when it happens to you can catch them in a much easier fight. As you're fighting this group, a second group of Covies appears on the ridge overlooking the area, 4 of their number being snipers. Aim your gun at them and take multiple foes out with the force of the blast.
The final wave will appear, with a good chunk of the Grunts and Elites carrying Fuel Rods. A third Wraith is brought in as backup, but since the Phantom has to fly very close to you to drop it it shouldn't be a problem. About half the foes are going to engage you, but the other half might try to retreat into cover again. Take out the fighting half first, then move the tank to the site of the first lookout tower in the area and blast the remaining foes away. If you get too overwhelmed and the tank catches fire, pilot it to one of the other tanks and hop out before it's destroyed. Even if you run out of tanks, you still have plenty of ordinance to use.