Armor customization

Armor Permutations are a feature in Halo 3, allowing the player to aesthetically customize their multiplayer character (the armour doesn't have any effect on gameplay).

Introduction
Permutations allow a player to customize his/her multiplayer character (either a UNSC SPARTAN-II or a Covenant Elite) by swapping different helmets, shoulder pads, chest armor, and detailed colors (primary color, secondary color, and armor detail). All permutations are aesthetic only and do not change actual gameplay in any way, shape, or form.

They were originally discovered in the foremost release of the Halo 3 Beta in internal hexadecimal codes by modders and were later confirmed to provide high levels of player customization by GamePro's June magazine issue. Calculated together, there are 187,947,000 combinations for the player to choose from.

Armor Permutations are available only in Halo 3 (at the beginning of the game, the only parts unlocked are the Mark VI Spartan Armor CQB Variant, and the Elite Commando Shoulders.), and are unlocked by achievements in both the Campaign and multiplayer modes of Halo 3 or by finding the hidden skulls.

NOTE: Bungie has confirmed that there will not be DLC armor permutations.

SPARTAN Armor Permutations
There are a wide variety of SPARTAN II armor permutations, with 11 helmets, 8 shoulder pieces, and 8 chest pieces for a total of 6,144 different SPARTAN armor permutation combinations: one helmet, two shoulder pieces, and chest piece per permutation, with the exception of the Rogue, Mark V, and ODST, which do not have either chest nor shoulder pieces.

Helmets

 * Mark VI: Default Unlocked.
 * CQB: Default Unlocked.
 * EVA: Unlock either Campaign Complete: Normal, Campaign Complete: Heroic or Campaign Complete: Legendary achievements.
 * EOD: Unlock the Campaign Complete: Legendary achievement.
 * Hayabusa: Collect all Skulls.
 * Security: Unlock all Halo 3 achievements
 * Scout: Unlock the Used Car Salesman achievement.
 * ODST: Unlock the Spartan Graduate achievement.
 * Mark V: Unlock the UNSC Spartan achievement.
 * Rogue: Unlock the Spartan Officer achievement.
 * Recon: Bungie employees, winners of tournaments/double exp weekends, and those that impress (or amuse) Bungie in any other way.

Shoulder Pieces

 * Mark VI: Default Unlocked.
 * CQB: Default Unlocked.
 * EVA: Unlock the Refuge achievement.
 * EOD: Complete the level The Ark on Legendary difficulty.
 * Hayabusa: Collect at least 9 skulls.
 * Security: Earn 750 of 1000 gamerscore on Halo 3. Due to inconsistency, this armor permutation is not always given at 750, whereas there are some reports that the Security Shoulders need a minimum of 800 gamerpoints, but the official guide to Halo 3 lists the requirements as 750. Even then the armor permutation may appear for a short time and then disappear, as has been reported. This permutation may need the player's model to have accessed online to unlock it. Another way to unlock is to gain 30 achievements.
 * Scout: Unlock the Mongoose Mowdown achievement.
 * Recon: Bungie employees, winners of tournaments, and those that impress Bungie in any other way.

Chest Armor

 * Mark VI: Default Unlocked.
 * CQB: Default Unlocked.
 * EVA: Unlock the The Road achievement.
 * Hayabusa: Collect 5 skulls.
 * Katana (Add-On): Unlock all achievements in Halo 3. (''Note, Katana is a sword on the back of your armor, which is a Hayabusa chest plate. Not a chest plate)
 * EOD: Complete the level Tsavo Highway on Legendary difficulty.
 * Scout: Unlock the Too Close to the Sun Achievement.
 * Recon: Bungie employees, winners of tournaments/double exp weekends, and those that impress Bungie in any other way.
 * Bungie: Bungie employees. The Piece looks similar to the EOD piece, and makes any Helmet piece appear to be on fire. The disadvantage is that the flames can be seen with the Active Camouflage on, lessening it's popularity, even though it is the Bungie staff trademark.

Sangheili Armor Permutations
There are a wide variety of Elite armor permutations, with 5 helmets, 5 shoulder pieces, and 5 chest pieces for a total of 625 different Elite armor permutation combinations: one helmet, two shoulder pieces, and chest piece per permutation.

Helmets

 * Combat: Default Unlocked.
 * Assault: Default Unlocked
 * Flight: Unlock either Campaign Complete: Heroic or Campaign Complete: Legendary achievements.
 * Ascetic: Unlock the Steppin' Razor achievement.
 * Commando: Complete the Overkill Achievement.

Shoulder Pieces

 * Combat: Default Unlocked.
 * Assault: Default Unlocked.
 * Flight: Complete the level The Ark on Heroic or Legendary difficulties.
 * Ascetic: Unlock the Overkill achievement.
 * Commando: Unlocked automatically after Auto Update 1 was applied on February 19, 2008. Originally, the Killing Frenzy achievement was needed to unlock the piece, but a bug prevented this.

Chest Armor

 * Combat: Default Unlocked.
 * Assault: Default Unlocked.
 * Flight: Complete the level Tsavo Highway on Heroic or Legendary difficulties.
 * Ascetic: Unlock the Up Close and Personal achievement.
 * Commando: Unlock the Triple Kill achievement.

Unlocking Permutations
Note: The Arbiter's armor cannot be unlocked. Note: The Recon Armor does in fact have Shoulder/Chest pieces, but they are not featured here. 300px All of the armor permutations.

Trivia

 * There was a prank pulled on April 11, 2008, on the 1UP show, which involved a falsified armor perm called the Assassin Armor.
 * Among the most popular helmets for the Elite armour classification is the Assault and Ascetic.
 * Among the most popular helmets for the Spartan classification is the Security, Rogue, and Hayabusa.
 * Among the least popular helmets for the Spartan armour classification is the EVA.
 * The Arbiter's armor was originally going to be included in the Elite armour selection.
 * The EOD armor chest is surprisingly like Mark V chest plate