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Aggressor Sentinel

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Halo Wars Sentinel Transparent
General information

First Seen

Forerunner-Flood War[1]


Combat, Defense and Maintenance

Approx. Size

160 cm (5 ft 4 in)[2][3]


Combat, Defense and Maintenance



Armament information

Primary Weapon

Sentinel Beam

Weaponry Strength



Energy Shields

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Sentinels! The holy warriors of the sacred rings.
—A Special Operations Sangheili exclaimed upon seeing Sentinels in The Arbiter.

Sentinels are a broad category of Forerunner-constructed robots designed to suppress Flood outbreaks, construct Forerunner structures 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 instrusion. The non-organic composition of the Sentinels make them ideal combat units against the Flood, an enemy which thrived upon the biomass of their fallen enemies - by deploying the Sentinels en masse, the Forerunners could battle the parasite without contributing to its numbers. Controlled by their own basic AI functions, as well as their Installation's Monitor, Sentinels patrol the Halo rings and destroy anything deemed to be a threat.[4]

When not in combat Sentinels serve as basic repair, maintenance and security drones for Forerunner installations and facilities where Flood samples are kept, working in conjunction with Constructors and Enforcers to ensure that the facility remains in working order. The Covenant viewed the Sentinels as "Holy Warriors of the Sacred Rings,"[5] according to them the same respect extended to other Forerunner relics.


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.[4] 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.

Sentinels are created at Sentinel Production Facilities,[6] massive floating platforms that are located on every Halo Installation. These Facilities produce all types of Sentinels when facing either a Flood outbreak or an external threat to a Halo Installation or Construct. These massive assembly lines at maximum performance can produce Sentinels at a very fast rate to either supplement existing Forerunner defenses or to replace those destroyed for whatever reason. Sentinel Production Facilities are not limited to just the Halo Installations, Production Facilities are located on every Forerunner Construct that relies on Sentinels for guarding, although these facilities are different in appearance and may be either ground or mobile based platforms.


The Forerunners refer to the Sentinels as "our very basic countermeasures", and they are the first automated defense systems employed to assist with a situation and generate a proper response protocol. While Sentinels are strong enough to handle a situation, they are more of a supplement rather than a reliable combat system. The Sentinels' weapons system are limited and not as powerful as some of the other Forerunner weapons employed against the Flood, and as such can only hold them at bay for a limited amount of time.

Because of their limited A.I, they are only able to handle situations on a basic scale, which makes them vulnerable to strategic Flood attacks. Because of their limited intelligence they are not often able to perform evasive maneuvers when facing imminent attack and are usually destroyed. In large overwhelming numbers Sentinels are more than capable of handling a situation until more permanent measures can be applied.

The Sentinel's energy shield is its primary defense mechanism - once taken down, the Sentinel is susceptible to any type of small arms fire, especially plasma weaponry. When the Sentinel has been damaged beyond repair, the Sentinel explodes violently and releases a powerful EMP blast. This is a strategic last resort, as the blast will disable any nearby electronics, including any weapons the enemy may be using.


Different variants of the Sentinel have been utilized for different combat roles, and can vary from construct to construct; the following is a list of all known variants of the Sentinel.

Sentinel MajorEdit

Main article: Sentinel Major

Sentinel Majors are larger, more powerful Sentinel models used for heavy combat situations. They provide backup for Enforcers in the event of a massive Flood outbreak or attacks on the Halo Installations. 


Main article: Enforcer

Essentially heavy Sentinels, Enforcers are equipped with a variety of offensive and defensive weaponry, including Pulse Beams, Missile Projectiles, Sentinel Beams, and dual Energy Shields covering both their top and bottom halves. They are designed to handle major Flood outbreaks but are also capable of defending their Halo Installation from external threats.

Onyx SentinelEdit

Main article: Onyx Sentinel

Onyx Sentinels both guard and make up the Shield World of Onyx. With the ability to combine themselves in order to increase their overall beam power, as well as a much more powerful individual beam, Onyx Sentinels are formidable opponents.

Super SentinelEdit

Main article: Super Sentinel

Considerably larger than normal Sentinels, Super Sentinels fill the same role of combating outside threats. Like Enforcers and Sentinel Majors, Super Sentinels are only seen on the field in an event of a massive Flood outbreak. They have the unique ability to stun buildings, vehicles, and infantry.

Protector SentinelEdit

Main article: Protector Sentinel

Roughly similar in appearance to regular Sentinels, Protector Sentinels occupy varying roles, from healing or shielding other units to offensive capabilities similar to other sentinels. 


Main article: Strato-Sentinel

Strato-sentinels are massive machines, used to construct large-scale installations including the Halo Array.

Unidentified Sentinel VariantEdit

Main article: Unidentified Sentinel Variant

The largest Sentinel variant seen to date, this Sentinel variant is able to level entire cities with its weaponry.


First appearing in Halo: Combat Evolved, the Sentinels play an important part in aiding John-117 through the Library as he attempts to recover the Activation Index. Once learning of Halo's true purpose the Sentinels, led by 343 Guilty Spark, become enemies of Master Chief as he attempts to destroy Halo.

In Halo 2, Sentinels, at one point, operated automated facilities, such as Threshold's Gas Mine, for "untold centuries". Evidence of this remains; some Sentinels have been seen repairing Covenant vessels as the Arbiter enters the main hangar with the Seraph fighter, a Sentinel fires a green beam at the Seraph—the same beam as the ones used by Constructors in Sacred Icon. In Halo 3, Sentinels are also seen on the Ark and aid John as he makes his way towards the cartographer. After the death of 343 Guilty Spark, the Sentinels once again become an enemy. A different variant of Sentinels have also been seen on Onyx; and serve as a shield to protect anything without proper clearance from getting near the Shield World.

In Halo Wars, Sentinels serve as backup units that can be built at a Sentinel Shop along with Super Sentinels. They cost 100 resources each. Their size is exaggerated in the game to the point that they are almost the same size as a Banshee.

In Halo 4, Sentinels appear again on Requiem performing maintenance duties in the various Forerunner facilities present on the planet. The Sentinels in Halo 4 are never seen as enemies. They tend to only hover around the area that they are seen in and only engage in combat once in the game against the Covenant. Later swarms of them can be seen aboard the Mantle's Approach. They appear in Spartan Ops to aid the player against the Prometheans.


  • In Ghosts of Onyx, an Onyx Sentinel approaches Ash, one of Kurt's Spartan-IIIs, and attempts to communicate with him, first in Latin, then in English. Later in the book, Dr. Halsey confirms that this drone was a Sentinel, therefore proving that the Sentinels of Onyx have a slightly more advanced AI than those of any other Installations (besides Monitors).
  • There is a lone Needler Sentinel found on the Halo 2 level Quarantine Zone. It fires sporadic Needler rounds and drops a Needler when destroyed. The Sentinel is a non-canonical glitch.
  • Chris Hughes created a crablike machine with many animating parts that gave the Sentinel life and character.[7]
  • On certain levels in Halo 3, it is possible to 'surf' on Sentinels, by standing on the furthest possible point from the front of the Sentinel. This is easiest on The Ark, at the point where the light bridge must be opened for the Scorpions and Warthogs. The Sentinel will, eventually, hover over the edge, holding you up 50% of the time. Remaining on top of the Sentinel allows you to reach inaccessible locations.
  • The Bubble Shield, created by ONI, shares many similarities to that of the shielding technology of the Sentinel, especially that of the model used at Onyx.
  • Sentinels share both similar design and functions to that of the P'fhor Defense Drones from the Marathon series. In addition, they share the same weaknesses of being unable to withstand Shotgun and Plasma Pistol/Fusion Pistol fire.
  • You can control a Sentinel in Halo PC using the DEV cheat. You could pick up and use the Assault Rifle, the Sentinel would properly use it when the player left the bot.
  • When Sentinels are your allies, unlike other allied AI, will not attack you if you kill them, specifically noted in Halo: CE's level, 343 Guilty Spark. The Sentinels don't respond to a comrade's death.
  • On the Ark, you can gently push a sentinel into a 'dormant state' using a chopper, that is, if you could fit the chopper through the door where the light bridge is. You can then jump on the sentinel, as it will awake after a few seconds.
  • In the Halo: Combat Evolved level Two Betrayals, in the section just prior to the chapterThe Gun Pointed at the Head of the Universe (where you have to destroy 4 Sentinels), a way not to lose much shield power or health is to fire an overcharged bolt at each whilst jumping behind a glass panel to let the pistol expel excess heat in safety. If done correctly, the Sentinels shouldn't have a chance.
  • In the Deliver Hope trailer, the shielding on the CCS-class battlecruiser appears similar to the energy shields on the Sentinels in Halo 3.
  • In Halo 2, if you destroy a Sentinel next to an ally it will respond as if it was your fault.
  • The lights at the tips of the Sentinel Beams when they are operated by the Sentinels are different in each game. In Halo: CE they are red, in Halo 2 they are orange, and in Halo 3 they are blue.
  • In Halo 2, a regular Sentinel may be destroyed with one overcharged bolt from a Plasma Pistol on any difficulty.
  • A video released by Halo: Waypoint shows Sentinels in multiple Halo 4 levels, including Forerunner.
  • Sentinels make a low pitched droning noise whenever they move in Halo 4.
  • They are not enemies in Halo 4 but are seen mainly as scenery. They have been seen attacking a pair of Mgalekgolo near the end of the Halo 4 level Requiem.
  • In Halo 4, Sentinels are allies and wield Sentinel Beams. However, when they are destroyed, they disappear into a small slipspace rupture, presumably due to Requiem's automated systems. As a consequence, they don't drop the Sentinel Beam.
  • When Sentinels are destroyed, they release a small EMP. Due to this fact, it is a bad idea to attack Sentinels with the Energy Sword or Shotgun.


Sources Edit

  1. Halo Legends, Origins
  2. Halo: CEA Kinect Library
  3. Halo.Bungie.Org: Scale Comparison
  4. 4.0 4.1 Halo Encyclopedia, Chapter 8, page 226/227
  5. Halo 2 level The Arbiter
  6. Halo Encyclopedia Chapter 8, page 226
  7. The Art of Halo, page 44

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