Rat's Nest

Rat's Nest is a Halo 3 multiplayer map released through downloadable content on December 11, 2007. Rat's Nest is a large indoor vehicles map that resembles an area from the campaign level Crow's Nest, with internal vehicle accessible roads, tight corridors, walkways suspended above areas and vents. In the distance, Pelicans and Hornets pass by. It was used by the UNSC as a weapons, fuel and ammunition storage facility up until the Second Battle of Earth. Above the UNSC facility is the source of Kenya's water supply, Mount Kilimanjaro.

On November 19, 2007, Microsoft released information regarding the first Halo 3 Heroic Map Pack. Rat's Nest is one of the maps included in this bundle. The map pack retails for 800 Microsoft Points ($10 USD), and was released on December 11, 2007. However as of March 25th 2008 the Heroic Map Pack is free of charge to all Xbox Live Members.

Description
This map is, essentially, a big figure 8 track (note, a digital 8, meaning vehicles must turn 90 degrees to cross straight from one side to the next). The map is very open and vehicle-based around its perimeter and center, with close combat and medium sized rooms everywhere else. It has two Warthogs and Mongooses parked outside of both bases, and small rooms connecting each base. On the edge of the road, there is a small outdoor road. On the upper road there is a Ghost and Sniper Rifle, below that Active Camo, then a Gravity Hammer and a machine gun turret above that, providing a commanding but exposed view, then the Rocket launcher by the cliff. A Pelican is positioned on a landing platform visible from the track, but it is unusable and inaccessible due to death barriers. Pelicans and Hornets fly by in the distance. (which can be shot down with a spartan laser)

Trivia

 * If you listen closely to the big green pipes, you can hear Drones flying and bumping into each other inside the pipes. This is no doubt a reference to Crow's Nest where you first hear Drones passing through the pipes, before breaking out and engaging the player.
 * Bungie stated in an update that the level includes actual rats. There are rats, but they are dead. If they were alive, they may have confused players by showing up as tiny blips on their radar. Strange enough, as they could have been edited to remove the blips like the Sentinels in Isolation, although they might annoy players with their squeaking and distracting movements.
 * There are Hornets and Pelicans seen flying in the background of the outdoor area. The both of them can be shot down with a Spartan Laser. In campaign Pelicans cannot be destroyed by a Spartan laser.
 * Rooster Teeth, the producers of the popular machinima series Red vs. Blue, made their D.I.Y video here and in the two other maps in the Heroic map pack.
 * Rats Nests code name was 'John Carpenter's Prince of Dorkness'.
 * This level was first announced on the Bungie Weekly Update of October 12, 2007.
 * It is possible to get vehicles next to the Pelican, but players will be killed if they get too close.
 * It is possible that Rat's Nest once belonged to NATO (Northern Atlantic Treaty Organization). This might be as in campaign a Marine states that the Crow's Nest was "built for some 20th century war". If you look closely above each of the symmetric main entrances, there is a faded NATO star next to the big A2.
 * There have been several sightings of the Ghosts of Halo on this map.
 * The venting area beneath the Ghost spawn can be accessed through the turret glitch and used to store weapons.
 * Rat's Nest makes a great default race track map due to its repetitive layout that has track ebbing in the exterior of the structure.
 * Along with Avalanche and Sandtrap, it is the only map to feature the Trip Mine by default.
 * Rat's Nest was also the setting for a short scene in episode three of the new Rooster Teeth series Red vs. Blue: Reconstruction. Rat's Nest is featured as the blue base where Caboose is stationed after being taken out of Blood Gulch when the base became obsolete. Agent Washington is sent to retrieve him and his fellow blue comrades are only too happy to give Caboose up after he has caused widespread havoc from talking to vehicles as if they were Sheila to killing his comrades.
 * Beyond the Hornets and Pelicans flying around the base, pillars of smoke can be seen in the distance. A hint that the Battle of Earth was happening.
 * It is possible to see the Portal storm above The Ark.

Strategies

 * On the first floor entrance to the center from your base, there is a wall that will have a Battle Rifle resting on it. This wall can be climbed on to help get a better view of incoming attackers on foot and make you a less like victim to grenades in that area. You may also pick up the Battle Rifle there to aid with this tactic, allowing you to lower an opponent's shields as they come in and drop down and beat them down.
 * At the beginning of the level, it will be of no surprise that everyone will want to get a hold of the Shotguns and Gravity Hammer, but near the Shotguns are Bubble Shields, picking this up and used correctly can help you get at least one of the Shotguns and possibly the Gravity Hammer without risking attack from Battle Rifles or Needlers.
 * A good form of defense for Assault and Capture the Flag is to stay up on the first floor of your base with a Shotgun, this allows you to pounce any attackers on the ground floor, Plasma Grenades are nearby for attacking vehicles, and you are normally at very little risk.
 * Another good form of defense is to have a Shotgun and the Rocket Launcher; the Shotgun to deal with the on foot opponents and the Rockets to deal with vehicles before they can get in, provided you are on the first floor instead of the ground floor.
 * Yet another useful trick in CTF is to jam the lower doorway into your base with a warthog.