At the beginning of the level you will see a clip showing what remains of a UNSCDF heavy installation that has been completely overrun by the covenant. Then you will start with Sergeant Forge in his Warthog. It is fitted with a GAUSS cannon and is very useful against light vehicles or pesky grunts to run over.
You will be in the graveyard of wreckage once known as the UNSCDF destroyer PROPHET. You have to gather a squad to take back the base. When you arrive at the first group, just keep your vehicle out of the way but close enough to see the enemy so that your allies can take them down. Your allies are invincible here, so don't worry. Once they are dead the squad will get into the nearby warthog and join your team. Now continue up the ice. When you get to the next area just wait again in the distance but make sure you can see the enemy so you can make sure that they are being killed like they should. You will gain two more warthogs and these, like the first you gained, only have the chaingun. When you climb the next hill, there will be an elite by itself so just send Forge up to take it out in 1–2 shots. Now there is a jump and two very large groups of grunts that are perfect to ram. The achievement called "Everything's Better with Bacon" in this level is to kill 50 grunts by ramming them with your warthogs. It would be a good idea to beat the level then comeback to do the achievement.
You will then see a ghost recon vehicle. Should be easy for Forge to take in 1–2 shots. Then take your warthogs over the destroyed bridge and there will be a squad of marines under attack ahead of you. let them take out the turret on the hill or it will rip your warthogs to pieces, including Forge. They will follow on foot and there will be a large scale battle ahead that begins to break up when you arrive. The grunts will be killed off quickly. Some jackals will be held up on the other side of the energy shield. There will be a bridge you cross just before you reach the fight and at the bottom of the small gorge there is a black box. Send one of your warthogs in to get it as soon as the coast is clear and you will have your first black box to the story line in the campaign menu. You can later get an achievement for collecting all the storylines. Send in your marines to take them out, chances are you will lose one or two marines in doing this. Then destroy the generator and invade the base.
When you arrive inside, the two wraiths (Covenant Heavy Tanks) will be destroyed by shortsword (smaller attack craft than the longsword fighter/bomber) attack runs. That is your cue to move in with your forces and take back the base. There will be three areas that have covenant. Each one has about 2–3 groups of grunts and elites. Then you will have the mission completed and can continue to the next or redo the mission to get anything you may have missed.