First, go onto The Ark: Mission Start on campaign.

After your first fight with the covenant, there will be a platform near the tunnel to your next fight. Get onto it and you will find two plasma cannons ,rip either one off and proceed to the next area.

Next, you have to drop the turret near the entrance of the tunnel and screw all the brutes. Once you have done that, the Hunters will have already been deployed, so grab your weapon and fire at will. Plasma Cannons are great at killing Hunters, they take them out real quick and stun them so they can't use their weapons.

If you run out of ammo, get a brute shot, they're pretty good too.