Mark 2488 Onager

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Mark 2488 Magnetic Accelerator Cannon
Production overview


Misriah Armory


Magnetic Accelerator Cannon



32.6 m (106.9 ft)

Ammunition type:

15 cm ferric-tungsten slug (1.1 gigajoules per hit)[1]


Electromagnetic linear motor

Rate of fire:

20 rounds a minute

Muzzle velocity:


Effective range:


Service history

In service:

Human-Covenant War


The Mark 2488 Magnetic Accelerator Cannon, formally designated 15 cm Mark/2488 1.1GJ MAC, also known as the Onager and often referred to as a "mass driver", is a stationary Magnetic Accelerator Cannon used by the United Nations Space Command during the Human-Covenant War.[2]

The Mark 2551/25cm Portable is an upgraded variant of the weapon brought into service after the war.

Design details[edit]

The Onager is capable of firing a 15 cm round with up to 1.1 gigajoules of kinetic energy.[2] It has five linearly arranged magnetic coils, each of which needs to charge individually before each shot. The weapon needs to cool off after every shot, and does so by opening a radial vent on the upper portion of the barrel. The weapon is operated from a small booth on the left side of the cannon.[3]

Operational history[edit]

During the Fall of Reach, a group of UNSC Marines installed an Onager on top of one of the planet's ship-breaking facilities in Asźod to protect the drydocked UNSC Pillar of Autumn. Emile-A239 manned the mass driver to fend off incoming Covenant Banshees and Phantoms before the Autumn could take off.[3] However, the Spartan was killed by a Sangheili Zealot, prompting SPARTAN-B312 to commandeer the cannon and successfully delay the Covenant assault on the Autumn by crippling an incoming Ket-pattern battlecruiser with a shot to its ventral energy projector.[3]


  • The Onager is named after a medieval siege weapon, which in turn takes its name from a horse species.
  • On the weapons statistics page, the description for the Onager is simply "I need a weapon", a reference to a line by John-117 in the opening cinematic of the level Cairo Station in Halo 2.
  • "S-239" is painted on the Onager's frame. This is a reference to Emile-A239, who was killed while operating the weapon.
  • The "using Onager early" glitch can be exploited so that a player can reach the driver before the scripted cutscene. This glitch can provide a player with an easy killing spree by shooting down Banshees, or avoiding enemy lances by shooting the Phantoms carrying them.


List of appearances[edit]


  1. ^ Halo: The Essential Visual Guide, page 114
  2. ^ a b Halo: Reach game stats
  3. ^ a b c Halo: Reach, campaign level The Pillar of Autumn