Sierra 117

Sierra 117 is the first campaign mission of Halo 3.

It takes place in a jungle. According to the Halo 3 E3 2007 Trailer, somehow the Chief arrives onto the Earth's surface. At sometime, the Chief recieves reinforcements from Pelicans as he defends them as they land, but not well enough for one Pelican to get shot down. About a third into his mission, he runs into Marines and confronts the Arbiter. This is where it is believed that the Chief and the Arbiter first meet and join forces.

Upon completing it on the Normal, Heroic, or Legendary difficulties, the player will earn the "Landfall" achievement and 20 Gamerpoints.