M9109 ASW/AC MLA
From Halopedia, the Halo wiki
50mm Point defence guns are used aboard UNSC Starships to protect them from enemy Fighters & Bombers. An example of this is the Halcyon-class Cruiser or, to be more specific, the Pillar of Autumn. 50mm point defence guns are usually controlled by AI's, however, UNSC personnel can also control the guns if there is no AI. There have been instances where crashed UNSC capitol ships have been stripped of these point defence weapons, and mounted in UNSC Marine bases to protect against hostile dropships and fighters.
