The Master Chief sends a team of Spartans to the surface of Reach to protect the MAC 's planet - based power generators .
The last line of defense for the planet is an array of magnetic accelerator cannons ( MACs ) orbiting the planet .
The Master Chief sends a team of Spartans to the surface of Reach to protect the MACs 's planet - based power generators .
The last line of defense for the planet is an array of magnetic accelerator cannons ( MACs ) orbiting the planet .