Forerunner automated turret

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The Forerunner automated turret, sometimes referred to as the autoturret and auto-turret, is a Forerunner construct similar in design to a Sentinel. As its name implies, the autoturret acts as an automatic antipersonnel weapon.

Overview
This small, robotic turret is a defensive piece of Forerunner technology that resembles a stripped down Sentinel. When deployed, it hovers in place above the ground, and will fire upon any enemy combatant who comes within range of its sensors with a deadly blue beam. The plasma-based projectiles are hot enough to melt steel.

Gameplay
The autoturret is a very useful suppressive equipment capable of taking out individual Covenant unit and Flood form with relatively short burst. Its only drawback is its slow target acquisition system: the autoturret takes a few second to lock onto a target. Because of this design flaw, the autoturret can be easily destroyed by a squad of Covenant soldiers or a swarm of Flood forms.

Its heads-up display symbol is a silhouette of the equipment itself, and slightly resembles the symbol for the Power drain.

Advantages

 * The auto-turret has enough power to remove a Brute's power armor, kill a Jackal and a Grunt with a single shot, and kill a Brute Chieftain within three shots. Also, the auto-turret's beam is powerful enough to push back any airborne enemies.
 * Even with its poor targeting and low damage resistance, the auto-turret can still often provide kills without considerable player support.
 * The auto-turret's firepower increases significantly as the game difficulty increases.

Disadvantages

 * The turret has a warm-up time of about three seconds. The turret also has problems picking out targets, often tracking allies with its targeting system (and occasionally shoots at the player).
 * When the turret is the player's enemy, the AI skill level is greatly increased. As with AI-controlled Marines, it will pick out targets faster, fire more accurately, and will rarely turn away from you on higher difficulties if you are in its sight.
 * It is rather fragile, easily being dispatched by enemy forces. Additionally, its sight is very narrow and can only attack enemies in front of it.
 * If bumped by the player or an enemy, it may go flying up into the air in an erratic manner.

Behavior against foes/allies
After the player has defeated 343 Guilty Spark, if the player deployed any Auto-Turrets outside the Control Room, they will turn against the player and fire at him/her. This could be due to the fact that a Forerunner construct has been destroyed, and any other Forerunner constructs in the immediate area must kill the construct's destroyer. Or that, as Guilty Spark betrayed you, he added you to the Sentinels "hostile list", making any Forerunner creation try to kill you. Another theory of why they behave in that manner is because the Monitor of the Installation has been destroyed, and without any protocol to follow, they fired at anything that moved. This includes the Master Chief and the Arbiter. When they are against the player, their shots are incredibly dangerous, strong enough to kill you in one shot on Easy.

On the level The Covenant, if you use an Auto-Turret during the part where you are allied with the Flood, the Auto-Turret and the Flood will try to kill each other. A canon explanation for this is that the Forerunners programmed their creations to kill the Flood, period. So it attacks the Flood and when the Gravemind sees this hindrance and tries to destroy. Or it might be that the Auto-turret is encoded into the level as a 'Forerunner team member', meaning its allegiance lies with Guilty Spark. When Guilty Spark, a member of the 'Forerunner team', becomes your enemy, it follows a script to break the team allegiance between the player (the Master Chief, and on Co-op, the Arbiter). This is also why the Flood and Auto-turrets fight each other, because while the player's allegiance is aligned with the Flood, the Forerunner and Flood teams remain enemies.

However, on the same level, when you get to the Separatist Phantom that arrives to pick up the Arbiter, if you destroy the Phantom (thus preventing Guilty Spark from departing) and you pick up and deploy an Auto-Turret, it will fire at Guilty Spark for unknown reasons.

Trivia

 * It is so far only encountered on the Halo 3 levels The Ark, The Covenant and Halo, and is not found on any multiplayer maps due to the issue of keeping the game balanced, and its inability to work with multiplayer netcode.
 * However, in Halo 4, a more balanced Forerunner auto turret is introduced as the Z-2500 autosentry.

List of appearances

 * Halo 3