Spartan Armor Variations
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EVA (Extra Vehicular Activity) Armor

Description: Extra Vehicular Activity Spartan Variant is a type of armor that focuses on greater vehicle activity. It was designed for improving mobility in zero gravity without the use of thrusters and increasing exo-atmospheric endurance.

EVA Armor - Complete Tsavo Highway on Normal, Heroic, or Legendary
EVA Helmet - Complete the campaign on Normal
EVA Shoulders - Complete the Ark on Normal, Heroic, or Legendary

EOD (Explosive Ordnance Disposal) Armor

Description: Explosive Ordnance Disposal is the detection, identification, on-site evaluation, rendering safe, recovery, and final disposal of unexploded explosive ordnance. It may also include explosive ordnance which has become hazardous by damage or deterioration.

EOD Armor - Complete Tsavo Highway on Legendary
EOD Helmet - Complete the campaign on Legendary
EOD Shoulders - Complete the Ark on Legendary

Scout Armor

Description: The Scout Armor is a variant that was tested alongside the Recon Variant. This armor has stealth capabilities.

Scout Armor - Get "Too Close to the Sun" Achievement
Scout Helmet - Get "Used Car Salesman" Achievement
Scout Shoulders - Get "We're In for Some Chop" Achievement

Security Armor

Description: The Security Armor is an old variant of the Mark V Armor, but is closely based on the marathon game. You can see if you look closely, that there is a marathon symbol above the visor.

Security Helmet - Get 1,000 Gamerscore points (earn all achievements)
Security Shoulders - Get 250 Gamerscore points

Hayabusa Armor

Description: The most unique armor that doesn't seem to fit into the Halo universe. That’s because it’s based on Ryu Hayabusa of the Ninja Gaiden Series and Dead or Alive. This suit is almost an exact Copy of the Future Ninja Suit.

Hayabusa Chest - Collect 6 hidden skulls
Hayabusa Helmet - Collect 13 hidden skulls
Hayabusa Shoulders- Collect 9 hidden skulls

ODST (Orbital Drop Shock Troopers) Armor

Description: Orbital Drop Shock Troopers (ODSTs), AKA Helljumpers, are an elite Special Forces group of the UNSCDF Marine Corps, commanded by Naval Special Warfare. They are dropped into their mission areas by an HEV (Human Entry Vehicle) low-orbit drop. This helmet will give a nice twist to appearance, causing you to look like the trusty, uber-marines, that you fight alongside with. Disguise yourself in the all-tactical helmet of the O.D.S.T.

ODST Helmet - Get "Spartan Graduate" Achievement

Rogue Armor

Description: The Rouge Helmet is the Mark VI (a) Variant which you get for being a Spartan officer. The Helmet is manufactured by the UNSC Private Sector.

Rogue Helmet - Get "Spartan Officer" Achievement

Mark V Armor

Description: The Mark V armor, as you most likely already know, is the armor that Spartans, including 117, were equipped with in Halo: Combat Evolved. It's pretty simple, just a model of the Mark V armor.

Mark V Helmet - Get "UNSC Spartan" Achievement

Mark VI Armor

Description: The Mark VI Armor is the default Spartan armor for both halo 2 and halo 3. It’s an upgraded version of the Mark V Armor from halo 1.

Katana Armor

Description: The katana is to be used as an extension of one’s arm for those intending to be warriors. It’s an unusable attachment to the back of the Hayabusa's body armor. You get this along with the security armor.

Katana Chest- Complete all achievements

Elite Armor Variations
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Ascetic Armor

Description: The Helmet of this armor has two blades sticking out of either side of it, quite befitting as the achievement to obtain it is Steppin’ Razor, a triple kill with energy sword.

Ascetic Armor - Get "Up Close and Personal" Achievement
Ascetic Helmet - Get "Steppin' Razor" Achievement
Ascetic Shoulders - Get "Overkill" Achievement

Assault Armor

Description: The second Elite armor permutation to be unlocked at the start of the game. It’s the only other variant aside from the default Elite and Spartan armors to be seen in campaign.

Combat Armor

Description: The Default Armor worn by Elites. And is thus far the only Elite armor to have an open mouth area, with small parts to armor the mandibles.

Commando Armor

Description: A specialist Elite armor for the Commando unit. It’s arguably one of the harder to obtain elite permutations.

Commando Armor - Get "Triple Kill" Achievement
Commando Helmet - Get "Overkill" Achievement
Command Shoulders - Get "Killing Frenzy" Achievement

Flight Armor

Description: Special elite armor for extra vehicular activity. This is a counterpart to the EVA armor.

Flight Armor - Complete Tsavo Highway on Heroic or Legendary
Flight Helmet - Complete the campaign on Heroic or Legendary
Flight Shoulders - Complete the Ark on Heroic or Legendary

Bungie Exclusive Armor Variations
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Bungie Armor

Description: The Bungie Armor is the cause of the flaming head, which is worn only by bungie.net employees. The flame works with any helmet as it is actually part of the body plate, which looks identical to the EOD, with only one difference, it produces a flame in the helmet.

C.Q.B. Armor

Description: Close Quarters Battle Armor is a type of armor that focus on, well, close quarters battle. It was designed to improve survivability in close combat; specifically by looking at alternate methods of K dispersal and improving joint mobility.

Recon Armor

Description: An armor that is a very rare variant. This armor also goes along with the flaming head Bungie armor. Only for Bungie employees, until Bungie decided to release it to certain individuals who did hilarious things unintentionally within the Halo 3 sandbox. Such as the Traffic Cone Death or the Self-Snipe Suicide. People can also earn this armor by creating an amazing level on forge as well.