Armor customization

"Armor Permutations" is a feature in Halo 3, allowing the player to aesthetically customize his/her multiplayer character.

Introduction
Armor Permutations allows a player to customize his/her multiplayer character as either a UNSC SPARTAN-II or a Covenant Elite, and change between 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 gameplay (no bonuses, increased hitboxes, etc).

They were originally discovered in the Halo 3 Beta hexadecimal code by modders and were 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 unlocked by accomplishments in either the campaign or multiplayer modes of Halo 3.

SPARTAN Armor Permutations
There are a wide variety of SPARTAN armor permutations, with 11 helmets, 8 shoulder pieces, and 8 chest pieces for a total of 5,632 different SPARTAN armor permutation combinations: one helmet, two shoulder pieces, and chest piece per permutation. This excludes color variations.

Helmets

 * Mark VI: Default Unlocked.
 * CQB: Default Unlocked.
 * EVA: Complete Campaign on Normal, Heroic, or Legendary.
 * EOD: Complete Campaign on Legendary.
 * Hayabusa: Collect all skulls.[There is no unknown skull]
 * Security: Get all achievements in Halo 3.
 * Scout: Complete "Used Car Salesman" Achievement.
 * ODST: Complete "Spartan Graduate" Achievement.
 * Mark V: Complete "UNSC Spartan" Achievement.
 * Rogue: Complete "Spartan Officer" Achievement.
 * Recon: Bungie Employees and selected few.

Shoulder Pieces

 * Mark VI: Default Unlocked
 * CQB: Default Unlocked
 * EVA: Complete The Ark on the Normal, Heroic, or Legendary difficulty
 * EOD: Complete The Ark on Legendary
 * Hayabusa: Collect 9 skulls [Unknown skull does not count]
 * Security: Get 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 require a minimum of 800 gamerscore, but the official guide to Halo 3 lists the requirements as 750. It has been suggested that meta-game achievements and Marathon Man are required.
 * Scout: Complete "Mongoose Mowdown" Achievement
 * Recon: Bungie Employees and selected few

Chest Armor

 * Mark VI: Default Unlocked
 * CQB: Default Unlocked
 * EVA: Complete Tsavo Highway on Normal, Heroic, or Legendary
 * Hayabusa: Collect 5 skulls [Unknown skull does not count]
 * Katana (Add-On) : Earn 1000 out of 1000 Gamerscore Points for Halo 3
 * EOD: Complete Tsavo Highway on Legendary
 * Scout: Complete "Too Close to the Sun" Achievement
 * Recon: Bungie Employees and selected few


 * Flaming Helmet Chest Piece: Bungie Employees only

Elite 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. There are probably fewer Elite armor permutations because (generally) fewer players play as Elites.

Helmets

 * Combat: Default Unlocked
 * Assault: Default Unlocked
 * Flight: Complete Campaign on Heroic or Legendary
 * Ascetic: Unlock "Steppin' Razor" Achievement
 * Commando: Unlock "Overkill" Achievement

Shoulder Armor

 * Combat: Default Unlocked
 * Assault: Default Unlocked
 * Flight: Complete The Ark on Heroic or "The Storm" on Legendary [Please note that due to complaints from the players about this permutation being glitched, Bungie has fixed this and after the auto-update, will automatically unlock for every player, even those who don't have the permutation unlocked.]
 * Ascetic: Unlock "Overkill" Achievement
 * Commando: Unlocked automatically after Auto Update 1 is applied

Body Armor

 * Combat: Default Unlocked
 * Assault: Default Unlocked
 * Flight: Complete Tsavo Highway on Heroic or Legendary
 * Ascetic: Complete "Up Close and Personal" Achievement
 * Commando: Complete "Triple Kill" Achievement