HIGHCOM Armory Omega is one of many weapon caches placed on Reach in times of emergency.
Background
It contained special weapons created by the ONI, such as the NOVA Bomb, as well as many standard infantry weapons and vehicles. This cache was found by Red Team during the beginning of their defense of Reach's Orbital Super MAC Guns generators. It is unknown what happened to the cache's supply of weapons, minus the NOVA, after the Covenant's glassing of Reach.