On this level you can find many Ghosts. There is no faster vehicle in this game so get it asap.
• Destroy first anti-air Wraith
Your first mission is to open the gates to make way for the Warthog and the rest of marines. Open all gates you can find but when you reach the battlefield do not attack yet. It's time for the next skull.
This skull is placed on the silo on the right side of the battlefield. To reach it get the Warthog and ride towards the silo. You'll see an elevated spot on the left side of the silo and that's the place to crash your Warthog in. Jump on the hood and then jump on top of the silo. The skull is yours.
Effect: All enemies and allies are equipped with more grenades and throw them more often.
There are two Ghosts in the hangar. Get one of them and clear the field. Take down the Wraith destroying the engine on its back.
• Destroy all other Wraiths
Move into the building but don't leave your Ghost yet. Get inside crushing any opposition. After a while you'll be on the next battlefield. Destroy Wraiths but be careful - Grunts in vehicles have tendencies towards going kamikaze, so destroy them before they get the chance to.
• Kill the Scarab Tank
After a short while another of your old friends will appear. The Scarab shouldn't be hard to destroy. Shoot its legs first. After it goes into a crouch enter the vehicle, and destroy the core. Run away, it's going to explode.
• Neutralize the anti-air cannon!
Follow the marines (unfortunately, you need to leave the Ghost). Before you reach the cannon, you have to go through the structure. Take a Battle Rifle with you. There are many Brutes inside, but they're walking in groups so you can use grenades to get rid of them. You can find some ammo near the exit. After a short while the next, powerful enemy appears, Hunters. Hide yourself and target their weak points (orange places on their back). All it takes are some well-aimed shots and they're down. Near the exit you'll meet some Brutes but it's nothing compared to the cannon crew. It's a good idea to take the turret first if you want to capture the hill and destroy the cannon. This way it will be much easier to destroy many Grunts and even the most dangerous Brutes. The cannon's weak point is on the bottom.