Mark 2551 Onager

The Mark 2551/25cm Portable Magnetic Accelerator Cannon, also known as the Onager, is an upgraded variant of the Mark 2488 Magnetic Accelerator Cannon developed by Misriah Armory. It uses a 25cm ferric-tungsten depleted uranium round that is fired at supersonic speeds.

Service history
The UNSC's postwar prototype flagship,, is equipped with a number of Mark 2551 MAC dorsal turrets. During the initial battle on the Forerunner shield world Requiem in 2557, these turrets were used to fend off the Didact's Cryptum, forcing the Didact to retreat after the ship's MAC network was reactivated by John-117. Along with Infinity's anti-aircraft batteries, the turrets shot down at least two s.

ONI's Ivanoff Station near Installation 03 made use of several automated Mk. 2551 Onagers for defense against space debris and later against at least three Covenant s when the station was attacked by Covenant forces under the command of the Didact himself. The station's defenses were reprogramed by Cortana to give the evacuating personnel covering fire against the attacking Covenant forces. The Onagers shot down multiple approaching Phantoms, though some managed to slip through their defensive fire to land troops on the station.

List of appearances

 * Halo 4
 * Halo: Escalation