Run straight for the Ghost. If you're good at shooting Grunts out of Ghosts, then go for it, but otherwise, chase it down and hijack. He rarely does a good job of evading you, so that won't be too difficult. Drive the Ghost to the Revenant that’s just past the tank. Hop into the Revenant and make your way to the AA Guns. For each AA Gun, wedge your Revenant inside and take down the shield, then shoot the core and move on. After the second AA Gun explodes, a timer starts counting down from about 1:14. you have until it reaches zero to kill both Fuel Rod Shade Turrets, so take your time, don't get splattered by the Revenant. If both turrets are dead when the timer reaches zero, the door to Sword Base will open. If they're not dead when the timer reaches zero, the door wont open until both turrets are dead. Anyway, once you blow up the second AA gun, drive up to the Ghost and hop in. Drive to a point between the two Fuel Rod Shade Turrets and DMR both of them. From here, drive over to the Revenant next to the entrance to Sword Base and kill the driver without getting splattered. Once the door opens, drive your way in and make your way to the room with a long spiral ramp leading to the top. Walk up the steeply slanted pillar thing in the middle and make your way up by crouch jumping onto the platforms. Make your way to the multiplayer map and run to the activate button. The fight is so large and there are so many enemies at any given time that there’s no way to explain “how” to do it. I suggest practicing the level multiple times and watching the world record run. You'll get a feel for it eventually.