COS-class Mjolnir

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HTMCC H3 COS Crop.png
HTMCC H3 COS Crop Back.png
Production overview

Testing site(s):

ANVIL Station[1]


MJOLNIR Powered Assault Armor[1]]



Technical specifications


Experimental counter-intrusion modules[1]

ANVIL cyber operations specialists use this chassis to mount experimental counter-intrusion modules.

COS-class Mjolnir is an experimental variant of MJOLNIR Powered Assault Armor, which was approved for testing on ANVIL Station.[1]


Design details[edit]

The COS-class bears a notable resemblance to the GEN2 models of the GUNGNIR-class Mjolnir, sharing near-identical torso chassis', shoulder pauldrons and forearm gauntlets.

Development history[edit]

COS-class was built in the skunkworks departments of ANVIL Station.[2] The suit was also tested on ANVIL Station, where the station's cyberintrusion specialists used the armour to test experimental counter-intrusion modules.[1]

In-game information[edit]

The COS armor set was first introduced into Halo 3's MCC port along with six other new armor sets, as part of Series 6: Raven. It was never available in Halo 3 for Xbox 360.[3]

Piece Description Unlock requirements (Halo 3) Unlock requirements (Halo: MCC)
HTMCC H3 COS Helmet Icon.png
ANVIL cyber operations specialists use this chassis to mount experimental counter-intrusion modules. N/A (MCC-exclusive) Series 6: Raven, Tier 53 Spartan Point 1
HTMCC H3 COS Chest Icon.png
Series 6: Raven, Tier 73 Spartan Point 1
HTMCC H3 COS LShoulder Icon.pngHTMCC H3 COS RShoulder Icon.png
Series 6: Raven, Tier 66 Spartan Point 1
HTMCC H3 COS Forearm Icon.png
Series 6: Raven, Tier 90 Spartan Point 1
HTMCC H3 COS Legs Icon.png
Series 6: Raven, Tier 71 Spartan Point 1

Production notes[edit]

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The COS armor set was originally created as a useable armor permutation for Halo Online, a cancelled Halo 3-derived multiplayer game developed by Saber Interactive and Innova Systems which was intended to be released exclusively in Russia for the PC. After the game's cancellation in 2016, the armor was one of six sets added to Halo 3 in The Master Chief Collection as part of the game's sixth season in 2021.

The suit set bears a notable heavy resemblance to the GUNGNIR-class Mjolnir seen in Halo 4 and Halo 5: Guardians, with the suit's internal game filenames even referring to it as such. In the original Halo Online game, the suit was known as GUNGNIR in the alpha builds, though was later changed to the name of Kaladbolg.


  • The armor's originally altered designation of "Kaladbolg" references "Caladbolg", a mythical, two-handed sword wielded by Fergus mac Róich, of Irish mythology.
  • In the real-world, COS is a military acronym, standing for Cyber Operations Specialist - the role employed by the COS armor.[4]


List of appearances[edit]

  • Halo 3 (First appearance; Halo: The Master Chief Collection-only)