Rat's Nest

Rat's Nest is a Halo 3 multiplayer map released through downloadable content on December 11, 2007.

Introduction
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 Battle of Crow's Nest.

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 retailed 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 extremely 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. Small rooms connect each base. Around the edge of the map there is a small outdoor road.

On the upper road there is a Ghost and Sniper Rifle. Below the upper road, an Active Camo. A Gravity Hammer and a machine gun turret are placed above that, providing a commanding but exposed view. The Rocket launcher is 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. The Pelicans and Hornets that fly by in the distance can be shot down with a Spartan Laser.

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 attackers on foot, and keep you protected from grenades. The Battle Rifle is a helpful weapon to use while on the roof. You can drop the enemies shield with the Battle Rifle and then jump down and melee them.
 * Grab the sniper and shoot enemies trying to claim the Ghost until an ally gets it or it is destroyed.
 * At the beginning of the match, everyone will be going for the Shotgun and the Gravity Hammer. Next to the Shotgun is a Bubble Shield. Activate the Bubble Shield and you will be protected from Needlers and Battle Rifles. If used correctly, the Bubble shield will gain you the Shot gun.
 * Do not drive extremely fast down the hallways with the Warthog, the gunner will have a harder time trying to hit the enemy Warthog. Gunners need to shoot the gunner, not the general vehicle. Enemy Gunners will take the same damage when being hit. If the Warthog is hit instead, damage will be reduced.
 * Running the flag through the middle of the course makes it harder for the other team to return the flag. It is always recommended to "Flag Run" in order for a greater distance to be covered.
 * The upper pipe can be jumped on top of. If you have a flag and you run on the pipes, enemies in warthogs rumbling toward your base will likely not even notice you.
 * The Active Camo can be quite useful in objective games, you can have a teammate enter and hopefully weaken the defenders allowing you to take the defenders by surprise and complete the objective.
 * 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.
 * Stay by the crates to hijack the Ghost, it speeds down when it has to turn and can be boarded with little difficulty.
 * In capture the flag, have some players in a warthog attack from the main entrance to the opposing base. You can swoop in grab the flag and take the secret pathway to your base.
 * Use the gravity lift on an incoming warthog and it may sail to the death barrier.
 * 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.
 * In Team Slayer, CTF, and Assault, the Ghost is one of the best ways to help your team dominate. Due to the Ghosts high speed, splattering opponents is easy. Since Rats Nest's main road doesn't consist of uneven terrain and sharp turns, controlling the Ghost, and fleeing opponents with heavy weapons are a blessing. Another thing to keep in mind, each of the teams spawn points are outside the bases, which means each team will usually spawn on the main road. So, with the Ghost, you can boost right through their spawn points, and wreak complete havoc.
 * If you have the bomb, move on the higher ground and go through the corridors. If a teammate comes to pick you up, get on, plant the bomb and hide. If any players come to disarm it, slaughter them.
 * It is kind of a choose your death choice when you hold the enemy's flag. If you venture outside, you will be splattered, sniped or gunned down. If you go inside you will be beat down or killed by a close combat weapon. Choose whichever path your team has an upper hand in.
 * In a game of Team Slayer ,if you gain the lead and have all members of your team pile in behind the fence using the aforementioned mongoose fence glitch, you are safe until the match is over. The only catch is that someone must guard the sealed door to assassinate any potential intruders.
 * Use both your Warthogs in the beginning, put them on each opening of the hall in the middle so that if any body walks through they'll be barraged with machine gun fire.
 * Get the Hammer or shotgun and camp at the enemy's base entrance pounding any defender in sight. When a teammate gets the flag, they won't have to wait for an escort on vehicle or on foot. That's where you come in, bring a regenerator or bubble in case things get sour.
 * In the smooth terrain, the Mongoose is a quick yet instant transport.
 * In CTF, have two snipers standing in the part where a player can go to any base, while having a person with plenty of grenades and a Flare throw those inside the opposing base. Get the flag and get out before the other team respawns. Have the snipers cover you on your way out.
 * On either side of the main opening to the outdoor area, there are fences with generators in them. You can get on top of these, and the barbed wire will camouflage you. Better yet, you can hop off of this to the top of the street lamp, and then to the next lamp. Most people don't look up, therefore providing you with chances to drop down and surprise or assassinate the enemy.
 * The tight corners and obstacles allow for hijacking to be much easier on this map.
 * If you crouch jump while on a gravity lift near the rocket spawn, you can hop over the fence. While here you are basically invisible, and even if you are spotted, the enemy team will have a lot of trouble getting to you.
 * Players enjoy ambushing anyone trying to take the rockets right behind the barricade. A few thrown grenades are easy to bypass this problem.
 * Another hiding tactic is to hide in the side tunnels of the base. These tunnels are rarely used.
 * Get a Brute Shot from one of the bases and hop into the riding seat and when a vehicle comes around the corner shoot it and derail the vehicle and then finish them off (use your radar so you know which corner to watch).
 * Get one of the trip mines and drive a vehicle (preferably a Warthog) into the middle of the road and then get out and throw the trip mine behind the warthog and so when someone tries to drive on the road it may explode.

Forge

 * On the turns in the "track" that goes around Rat's Nest, place shield doors there, this will allow a vehicle to "bounce" off them around the turn.
 * Placing a Portable Gravity Lift directing vehicles outside the map will be challenging for everyone.
 * If you place multiple barricades on top of each other spanning the main vehicle route you can crash through and make a great machinima clip.
 * There are two "command post" rooms at the very top of the map. To get inside these rooms, create a tower out of available materials, and once you have reached the appropriate height, place a machinegun turret against the glass. Hop onto the turret and look up. Then go into Editor mode and you should be inside the room. Alternatively, float a teleporter upside-down, so the bottom of the teleporter is pressed up against the bottom of the room. Because characters always spawn rightside-up, (no matter how the teleporter is turned) and because there is a slightly wider teleporter radius on the bottom of the teleporter than on the top, characters teleport inside. Do this with a 2-way node to get out again. (Note: The 2nd "command post" room that is on the inside of the complex is shaped like a short "m". Sometimes teleporter nodes register as being blocked when trying to go through in this manner, but jumping into the sender teleporter or moving the receiving teleporter will get you a better connection.)

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 later in the level.
 * 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, even though this is present for the Monitor on Cold Storage. 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.
 * 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 Nest's code name was 'John Carpenter's Prince of Dorkness'.
 * 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.
 * The venting area beneath the Ghost spawn can be accessed through the turret glitch and used to store weapons.
 * Along with Avalanche and Sandtrap, it is the only map to feature the Trip Mine equipment by default.
 * It is possible to get behind a small fence on the side of the base that opens out into a cliff. To do this, drive a Mongoose with its left side facing the sealed door in the fence and get out. You will jump through the fence into a little caged area.
 * 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 is occurring.
 * It is possible to shoot down both the flying Hornets and Pelicans in the distance with a Spartan Laser, although it is very hard to hit the Hornets as they move abnormally fast and are very distant; the Pelicans are only slightly easier to hit.