The Z-1500 Automated Systems Drone, also known as an Aggressor Sentinel and by the Covenant as “Holy Warriors of the Sacred Rings,” is a broad category of Forerunner-constructed robots designed to suppress Flood outbreaks, construct and maintain Forerunner structures, mine and retrieve raw materials, and protect Forerunner technologies from alien lifeforms. To this end, they possess limited artificial intelligence and boast a wide range of weaponry and equipment in the field.
Following the construction of the Halos, Sentinels were built to serve as the first line of defense against Flood outbreak and external intrusion. The non-organic composition of the Sentinels allowed the Forerunners to battle the parasite without contributing to its numbers. Controlled by their own autonomous AI and their Installation’s Monitor, Sentinels patrol the Halo rings and destroy anything deemed to be a threat.
Sentinels are grayish-white in color and have two arm-like appendages with two grapple fixtures at the end of each arm, along with a central “head” and a curved undercarriage containing a Sentinel Beam. The form of a Sentinel may differ depending on the situation of their Installation.
Their powerful offensive beam weapons and defensive energy shield make them very effective in combat against intruders or foreign objects that present themselves as threats. Their smaller lasers are used for both repairing damaged Forerunner constructs, and self-repair should the Sentinel be damaged in combat. Sentinels are propelled by both an anti-gravity unit located on the undercarriage and small engines on the back of the unit. They are capable of traveling at high speeds but cannot sustain long range travel.