Point-defense gun

Were you looking for the AAA Helix Gun?

A point-defense gun is a type of United Nations Space Command starship-mounted weapon. Though several models exist, the most common type of point-defense gun fires 50mm high-explosive projectiles.

Functionality
The point-defense gun 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 also lesser "dumb" AI's.

Operational history
Point-defense guns have been standard armament on UNSC vessels since the Insurrection, a common model being the AAA Helix Gun.

During the human occupation of Installation 04, the ODSTs that recaptured and secured the wreckage of the from the Covenant managed to scavenge several dual barreled 50mm turrets. The ODSTs utilized the scavenged defense weapons and used them as anti-air defensive emplacements at Alpha Base.