The heaviest class of combat robot in the United Statesmilitary, the sentry bot sacrifices speed and maneuverability for sheer resilience and overwhelming firepower. The sentry bot had become a standard piece of military equipment by at least 2063, with prototypes existing further back. While the assaultron is designed for melee combat and the Mister Gutsy is a jack-of-all-trades, the sentry bot's purpose is to engage the enemy at range with a variety of weapons, including miniguns, Gatling lasers, rocket launchers, and even back-mounted cluster grenade launchers, while its thick armor and multiple redundant systems allow it to survive extended engagements. It's commonly considered to be one of the most dangerous robots ever created and RobCo Industries' finest fighting robot. Late models are also provided with the ability to self-destruct to prevent enemy from recovering the robot. Early sentry bot models were issued serial numbers in the SB-#### format (model, then serial), with later models transitioning to the standardized alphanumeric registration in the ABC-###### format.
The Appalachian variant of the sentry bot is identical to the variant of sentry bot used in the Commonwealth. They appear to have a bulkier construction and are substantially more resilient than their counterparts in the Capital and Mojave Wastelands. The typical weapons loadout of the sentry bot remains the same as seen in previous games, with a missile launcher and minigun being the norm (except these miniguns appear to be unique three barrelled variants chambered for the 5.56mm round). However, alternate weaponry configurations such as dual miniguns can also be observed.
On top of their already formidable ballistic and explosive weaponry, sentry bots have powerful melee attacks and a self-destruct function with equivalent power to a mini nuke. Despite their bulky armor and appearance, they are capable of moving stunningly fast and traversing extremely rough terrain (even scaling rocky outcrops with little difficulty that residents would struggle to jump up on). In addition; a sentry bot's entire torso is capable of rotating independently of its legs, functioning akin to a turret, and allowing it to move in one direction while shooting in a different direction (potentially against targets directly behind it). Sentry bots also appear to use Mecanum wheels that allow it to strafe right and left without having to turn.
Sentry bots are some of the rarest and the most difficult robots to defeat - fast, agile, heavily armed, and resilient enough to absorb a direct hit from a mini nuke. After losing both main weapons they will initialize their self-destruct sequence and charge at the player character. Even with their ranged weaponry intact, sentry bots often charge into close combat to deliver powerful blows with their arms if one ventures too close, thus deterring attackers from any use of melee weapons. Since all variants explode on death with the force of a mini nuke, this tactic may prove even more dangerous to their opponent than their devastating long-range firepower. However, should a sentry bot engage the player character for too long, they will eventually enter a cooldown period, blasting steam out of their back and exposing their dual fusion cores. Hitting exposed fusion cores is the best way to cause damage to them. After their death explosion, the sentry bot becomes a charred, blackened version of itself, and is safe to loot then for various scrap, ammo, and maybe a surviving fusion core.
Should one encounter a legendary sentry bot of any kind, keep in mind that all legendary robotic enemies explode upon death. This explosion does not override the sentry bot's built-in self-destruct, which means a legendary sentry bot will explode twice. Both explosions are equivalent to a mini nuke in power and occur with a short delay of a few seconds.
A much stronger version of the regular Annihilator sentry bot, armed with both the arm-mounted machine guns and a pair of mortar launchers on its back. Two serve as security for the core of MODUS in The Whitespring bunker, painted in the black of the Enclave with the 14 stars from the U.S. flag clearly seen on their chests. Other Annihilator sentry bot Mk.II are painted all black.
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A generally non-hostile sentry bot. It is white in color and only encountered within the Whitespring Resort. It will attack other hostile creatures which come into its range, but will only attack the player character if provoked.
An aggressive sentry bot, sometimes found at or near Hornwrightair purifiers, as well as the Mount Blair trainyard. It is involved in the Battle Botevent quest, and holds security protocols. This sentry bot is unique in that it is armed with flamethrower weapons in place of the standard tri-barreled machine guns and painted red compared to the white of the Whitespring sentry bots or black like those of the Enclave.
↑Fallout 4 loading screens: "The Sentry Bot is one of the most dangerous combat drones ever created, and utilizes a variety of heavy weapons systems to destroy its enemies. Upon death, it erupts in a devastating explosion."
↑Serial numbers in Fallout 3 and Fallout: New Vegas.