M9109 ASW/AC MLA

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 ship AI's.

On Alpha Halo, the ODSTs that recaptured the Pillar of Autumn scavanged 50mm Point Defence Guns from the Autumn and mounted them on Pelicans for transport to Alpha Base.