From Halopedia, the Halo wiki
This is about the Forerunner constructs. For the UNSC AI type, see Navy Sentinel. For the achievement, see Sentinels (achievement).
Sentinels are machine-servants created by the Forerunners, designed for the construction, maintenance and defense of their structures and facilities. Various Sentinel variants exist, each tailored to a specific task; because of its ubiquity, the Aggressor variant is often referred to simply as the "Sentinel". Most variants are produced by Sentinel manufacturing facilities, Sentinel factories, or Sentinel launchers. The Sentinels were revered by the Covenant as "holy warriors of the Sacred Rings", despite engaging them in combat on various occasions.
The Sentinels follow the command of the monitor or other ancilla that is in charge of the facility they are assigned to, but even without central direction, they are able to respond to threats against their assigned installations with remarkable coordination and effectiveness. On Installation 00, a sentinel defense network is used to coordinate the Sentinels on the Ark despite the monitor no longer being present. Sentinels follow their directives even if this entails engaging other Forerunner machines. For example, the Aggressor Sentinels of Requiem remained loyal to the Librarian against the Didact's Prometheans in 2557. Another instance is when the Constructors of Genesis remained loyal to Monitor Exuberant Witness against the Created's Promethean forces in 2558.
Sentinel Defense Network
A Sentinel Defense Network is a system that coordinates sentinel defenses to perform their duties in defense of an installation. All Installation has the Defense Network installed and each has its own protocol. Without the defense network activated, Sentinels are unable to perform their duties. This, however, does not affect the stationary defenses, which remain active even if the defense network is shut down, including containment shields. The Defense Network itself is separated to local and global defense network. The local defense network only controls sentinels surrounding terminals, while the global defense network controls defenses on a global scale. The Defense Network is linked with every defensive protocol on the installation. Containment protocol on Installation 00 is linked with the Defense Network and Sentinels cannot conduct the protocol if the network is disabled.
Installation 09 heightened the security protocol and immediately launched a Retriever Sentinel to cleanse the humans and the Banished present on the rings as soon as it left Installation 00. Professor Anders successfully hijacked the local network through the control tower to temporarily take control of Retriever Sentinel to disable barriers around the control room.
The Smart AI Isabel manipulated the Sentinel Defense Network to her own ends by hijacking Enduring Conviction and firing its energy projector on the Ark, causing Aggressor Sentinels to swarm on the ship and bisect it.
When Voridus shut down the Sentinel Defense Network, all Sentinel activities are ceased immediately, giving Voridus a clear path to the High Charity without any opposition. When Voridus reactivate the Sentinel Defense Network, the Sentinels were immediately resumed their duty, allowing Pavium and Voridus to call in Retriever Sentinel to defeat Proto-Gravemind.
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