M9109 ASW/AC MLA

A Point-Defense Gun is a United Nations Space Command starship-mounted weapon that fires 50mm High-Explosive projectiles.

The 50mm Point-Defense Gun (also known as the Helix AAA) functions much like the CIWS designs created during the 20th Century, firing 50mm projectiles. Unlike Archer missiles and the MAC weapon systems mounted on capital ships, the Point-Defense Guns are not used to engage Covenant capital ships, instead meant to intercept smaller threats like Seraph fighters or Boarding Craft to prevent (or at least lessen) the damage inflicted to a warship.

Because Human operators lack the reflexive responses necessary to operate the Point Defense Guns to maximum effect, the autocannons are computer controlled and, if an AI is available, control is diverted to it. "Smart" AI's seem better able to operate the Point-Defense Guns than standard computers and even lesser "dumb" AI's.

During the Human occupation of Alpha Halo, the ODST's that recaptured and secured the wreckage of the UNSC Pillar of Autumn from the Covenant managed to scavenge several dual barreled 50mm turrets, using them as anti-air defensive emplacements at Alpha Base. These were not fitted to the Pelicans for use, but were carried underneath the dropships for transport to Alpha Base.