Part 1: Cairo Station
After the cutscene turn left on the stairs and pick up the Battle Rifle on the wall, you can wield dual SMGs instead, or wield a Battle Rifle and one SMG as used in this walkthrough. Link up with the Marines and Sergeant Avery Johnson and make your way to the end of this room, you can pick up a Pistol and swap it for one of your current weapons, but leave that for now. Walk through the door and into the next hanger.
 Part 2: Home Field Advantage
Covenant troops will blast through the door as a grunt slice it open, the first wave consist of Minor Grunts and Elites. You can take them out using the Battle Rifle while on the bridge, then get down to face the second wave. Swap your Battle Rifle with a Plasma Rifle and take out the next wave. Turn left and take out another group of Covenants using the SMG, and resupply from the SMG on the other side that is blocked by fire. Get up on the stairs next to a Marine on a machine gun and get in the next room. Get on the Machine Gun Turret and take out the Grunts and Elites on sight, get to the end of the room and downstairs, take out the Elite and the Grunt. Another Elite will dash in, take him out and recharge your Energy-Shield. Note that it is better to use SMGs against Elites and Battle Rifles against the Grunts.
Regroup with the Marines and take out the Grunts in the current room, two separate waves of Elites and grunts will arrive at once from both blast doors at the end of the room. Step back for a distance and use your Battle Rifle to take them out. Next, get to the room at the left and take out the Elite, your own your own now, the Marine won't fallow you at this point. Move up on the stairs and get into the next hanger. A bunch of Covenants will drop in from their ship, leave them for the Marine on the turret for now and pick up the scattered frag and plasma grenades, Jump to the ground level and take out any remaining Grunts. Another wave of Covenants will arrive shortly through a door next to the Pelican, toss a grenade and take out the Elite first then the grunts. Move to the hallway they came from and into the entrance of the next hanger. Take out the Grunts on the bridge first, and quickly get to the end of the room to flank the Covenants dropping from the ship, it is better than taking them out alongside the Marines. The Covenants may toss a Plasma Grenade here, so be careful. Cortana then found out about a bomb that the Covenants brought in.
 Part 3: Priority Shift
Go to the room that contains a dead Marine and a bunch of Frag Grenades, resupply and get back to the hanger, toss a grenade downstairs to the room that leads to the Mac Storage. Take out the Grunts and the Stealth Elites, pick up ammo and get into the Armory where you started the The Armory level. The Master Gunnery will be killed instantly, so don't bother rescuing him, take out the Elites and take cover to recharge your Energy-Shield. Swap for the Shotgun, you should have it and an SMG by now, and get into the next hall. Get close to Grunts and waste your Shotgun ammos on them, use the SMG on the Elites then get rid of the Shotgun when the room is clear, keep your SMG and pick up a Plasma Rifle. Get to the next room and take out the grunts on the Plasma turret and go upstairs, and into the next room. Take out the Grunts and the Major Elite, then swap for the Battle Rifle and grab a new Plasma Rifle. Move into the next hallway and regroup with Miranda Keyes and Johnson. Assist them and take out the Covenant waves and move into the next hallway.
 Part 4: Authorized Personnel Only
A door will blast open, take out the two Elite Rangers and move out to the space, Jump down on the Ship's surface but not on in the blank space. Take out the Ranger Elites and make your way to the airlock and back into the Ship. A group of Drones will show up, take them out and restock, then take out the Covenant troops on the lift and activate it. When it stops descending, restock from the bodies in the airlock and take out the Ranger Elites. move forward and get in the elevator behind the Plasma Turret.