Invasion

Invasion is a gametype in Halo: Reach. An alternate mode of the gametype is a variant called Invasion Slayer, which is a six-versus-six Spartan-vs-Elites slayer variant.

Overview
Invasion is a team-based gametype and can be described as a large vehicular-based firefight. The game begins on Phase 1, where only one portion of the map and no vehicles are available. As the game continues, more Phases unlock meaning there will be more objectives to be completed, vehicles will become available, and more Loadouts will become available as well. Boneyard's version of Invasion features the Elites on the offensive, trying to obtain a UNSC data core with valuable information on it, while the Spartans are tasked with defending it.

Invasion Slayer is a six-versus-six Spartan -vs-Elites slayer variant where players will eliminate the opposing team in order to score points; obtaining a total of 100 kills will end the game. Similar to the default Invasion gametype, the slayer gametype will be regulated through Phases which can be unlocked by either acquiring a specific amount of kills or surpassing a specific time.

Players will not be able to choose which multiplayer model/teams they want to play in Matchmaking; the system will automatically assign the player to play as either a SPARTAN or an Elite.

Phases
The default Invasion gametype is broken into three phases; successfully completing an objective in one phase will unlock the next phase. If the Spartans can hold out during any one phase, the game is over and they score a victory. As a result, UNSC Longswords will fly overhead and clear the zone with a tactical strike, rendering any and all data stored on the core completely destroyed. Should the Elites be in control of the current objective, the game will go into Sudden Death mode where respawning is disabled.

In the Invasion Slayer gametype, each team has to reach a certain amount of kills or surpass a certain time period in order to proceed towards the next phase. Similar to the default gametype, new loadouts, weapons and vehicles will be available to the players as they proceed towards the next phase.

Phase 1
Phase 1 requires the Elites (Attacking Team) to shut down one of the two generators positioned inside the Commonwealth. The process of shutting down the generators requires 20 seconds. Successfully shutting down one of the generators will disable the security systems that leads to Phase 2 and the match will be extended for an additional four minutes. The Spartans (Defending Team) will win if the Elites fail to shut down the generators in less than four minutes allotted in Phase 1.
 * Default

Phase 1 is the first phase of the Invasion Slayer gametype and ends once the scoring reaches 25 kills or the timing reaches four minutes. The next phase will be unlocked if any of these markers are surpassed.
 * Invasion Slayer

Phase 2
Phase 2 requires the Elites to control one of the two newly marked territories; one located inside the refinery and the other located beside the Spartans' vehicle bay. Similar to Phase 1, a total amount of 30 seconds is required to successfully shut down the security systems. During this phase Elites gain a Ghost and a Wraith for their use, and the Spartans get a Warthog. Successfully completing Phase 2 will leave the data core exposed for Phase 3 and add an additional four minutes to the match. Elites will keep a total of two loadouts but with more powerful weapons, in addition, they will also get a weapons cache with a plasma launcher and/or a focus rifle. Spartans will also get two loadouts as well.
 * Default

Phase 2 is the next phase of the Invasion Slayer gametype and ends once the scoring reaches 50 kills or the time limit reaches eight minutes. The next phase will be unlocked if any of these markers are surpassed.
 * Invasion Slayer

Phase 3
In Phase 3, the Elites must retrieve the data core and deliver it back to the Phantom hovering onto the scaffolding near the ridge. When carrying the data core, the carrier's movement will be hindered by the package, similar to that when carrying support weapons in Halo 3, and will be left defenseless and vulnerable to the Spartans. Elites will unlock a Banshee in this phase, and Spartans unlock a Scorpion Tank. The Elites win when they successfully deliver the data core to the Phantom, also ending the game. Elites will have four loadouts. Spartans will have four equally powerful choices.
 * Default

Phase 3 is the final phase of the Invasion Slayer gametype and ends once the scoring reaches 100 or the match's time limit runs out. Surpassing either of these markers will officially end the game. There are also several areas to capture, once captured reinforcements will be dropped to your base. The higher your score the better the reinforcement.
 * Invasion Slayer

When the core is returned the announcer actually says flag returned.

Invasion SPIRE
Invasion has now been confirmed to take place on Spire, a map not included in the Halo Reach Beta. It will have reverse roles; Spartans will be on the offense trying to capture a tower held by the Elites. Vehicles that will be on this map include: Falcons, Banshees, Revenants, and Ghosts. There will be stationary plasma turrets for use along with multiple snipers for use on the platform and around the battle field. Similar to the Boneyard invasion, there will be 2 optional places to capture in both the first and second phases. The details are unknown, but it will end with the Spartans taking the Data Core to a Pelican on the beach. Or the Elites defending the core until the time limit ends.

Trivia

 * A bug in this gametype during the multiplayer beta swapped each team's role, causing the Elites to defend the Core while the Spartans tried to steal it. This also swapped the Loadouts for both teams, making Elites gain access to Spartan loadouts and vice versa, but this bug was fixed for the final game.
 * Even though the default setting for Invasion is 6 vs 6, you can increase the maximum players up to 8 vs 8 in custom games
 * The "Marksman" Loadout was removed from the first phase of this gametype during the multiplayer beta due to Spartan players able to get multiple kills on Elites with virtually no cover.