Sierra 117

Sierra 117 is the first campaign level of Halo 3. It is the first to feature real gameplay, as opposed to Arrival, which is merely a cutscene and tutorial. Also, take note that this is the First Level that features messages from Cortana on certain occasions.

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

Setting
LEAKED SIERRA 117 video

This level takes place in an African jungle, as confirmed via the hexadecimal code of the Halo 3 Beta and physically confirmed in the Halo 3 E3 2007 Trailer and the short video subsequent Bungie Podcasts. The jungle is home to a Covenant Loyalist encampment, and hosts lush verdant forestry, rivers, rocky landscapes, waterfalls, and tunnels.

Plot
According to the Halo 3 E3 2007 Trailer, Chief joins forces with the Arbiter and a few Marines. They progress through the area, securing landing zones for Pelican Dropships and defending them against enemy Banshees. If one makes inferences based on the Halo 3 Zune Concept Art and the beta code's level names, the level will culminate at an arrival at the Halo 3 UNSC Base.

It was stated in the September 07 issue of Gamepro that the Chief would have to rescue Johnson from a downed Pelican.

Transcript
The following transcript is incomplete, but is based on incomplete resources on Sierra 117's gameplay.

01: Walk It Off
Marine: "Sergeant Major, Phantom in bound." Johnson: "We stick together, we're gonna get spotted. We split up, and meet back at the LZ. Chief, go with the Arbiter, head toward the river." {some time later} Marine: "Sleepers! Take 'em out, nice and quiet! Jackals, on the ridge! Stay low, looks like they've got Carbines." {Short pause as Marines move out} Marine: "I hate it when I'm right!" Johnson (radio): "Pelicans are en route, Chief, but I can't reach Bravo. If you find him, get him to the extraction point." ''{A Brute is torturing a Marine on a log. It is optional to save him}'' Brute: Tell me its location! Gunnery Sergeant Reynolds: Kiss...my...ass. Gunnery Sergeant Reynolds(if saved): "Brute Chieftain and a Phantom. They pinned us down...Killed my men." Johnson (radio): "Chief, Pelicans are at the river. We've got company, so I'll set up." Arbiter: "The river. Hurry." (Master Chief's HUD flickers and disappears, and translucent images of Cortana appear.) Cortana: Could you sacrifice me to complete your mission? (An image of Cortana in pain is seen) Cortana: Could you watch me die? Marine 1: Sir, you okay? Sergent Johnson: Your vitals just pinged KIA... well, let's do this.

02: Charlie Foxtrot
{SPARTAN-117 approaches a river where two Pelicans are trying to land} Echo 51: "Break off, now!" {Enemy Banshees begin strafing runs against Pelicans} Kilo 23: "I'm hit! I'm hit!" Johnson: "Can you hold?" Echo 51: "Negative, negative! I'm going down!" NEW OBJECTIVE: Locate Johnson's crashed Pelican (possibly later in game)

Trivia

 * Note that the level is called Sierra 117; Sierra is the word used in the NATO phonetic alphabet to represent the letter S, which, when used in a military sense, generally stands for "sniper." However, in Halo 3, it is S 117 which corresponds to SPARTAN-117. This has been confirmed in the second Bungie Podcast.
 * In the August 2007 EGM Halo 3 Story, Sierra 117 mistakenly said to be the fifth Level in the Halo 3 Campaign.
 * Jumping into the deep water at the point where the pelicans are shot won't kill you or even lower your shields. Also you can see fish swimming and even kill them. (These are what the small yellow dots are on your motion tracker)

Links
External -A leaked video from E3 2007.