Converging beam cannon
From Halopedia, the Halo wiki
Converging beam cannons are a kind of weapon system employed aboard Forerunner warships. The beam cannons are directed-energy weapons that fire upon enemy vessels and provide a path for follow-on antimatter streams, which destroy everything they touch. Aboard Forerunner vessels, these weapons were wielded by Warrior-Servants. Twenty-eight of these weapons are part of the armament of the Sojourner-class dreadnought, while the Mantle's Approach employed 25,000 these such weapons. The Guardian Custode each carry six converging beam cannons, which were considered more than adequete to defeat fleets of primitive capital ships, but did little when facing Forerunner ships controlled by the Flood.