Combine Sentry Gun

{{Weapon Infobox
| image=FileCombine Sentry Gun.jpg|130px
| image2=
| name=Combine Sentry Gun
| affiliation=Combine
| manufacturer=
| model=
| type=Autonomous pulse sentry gun platform
| damage=3 (per bullet)
| magazine=
| magtype=
| maxammo=
| fire=
| ammotype=
| operation=
| rate of fire=High
| recoil=
| spread=
| projectile speed=Fast
| accuracy=Medium
| range=
| maker=
| usedby=*Overwatch Soldiers
*Alyx Vance
*Gordon Freeman
| counterpart=Other CategorySentry weapons|sentry weapons
| counterwep=*Gravity Gun
| entity=*npc_turret_floor (''HL2'')
*npc_sentrygun_mp (''Survivor'')
| designer=
| hidep=
| hidet=
| hideu=
| hideg=
{{Quote|I can reprogram these turrets to attack the enemy. You set them up to defend the control room.|Alyx Vance|Half-Life 2|Fileal icanreprogram.ogg}}

The '''Combine Sentry Gun''',''Half-Life 2 Prima Guide'' also known as '''Sentry''', and referred to by the Overwatch as '''Sterilizer''' and '''Turret''' by the Resistance, is a fully autonomous tripodal pulse weapon featured in ''Half-Life 2'' and its episodes, commonly used by the Combine to guard WikipediaChoke point|chokepoints and vital areas. It is also available in the battle mode of ''Half-Life 2 Survivor'' as a placeable item.

In terms of gameplay, it is the successor of the Sentry Gun featured in ''Half-Life'' and its expansions, and the predecessor of the Aperture Science Sentry Turret|Sentry Turret of the ''Portal'' series.

FileDepot Sentry firing.jpg|left|150px|thumb|A Combine Sentry Gun firing at Overwatch forces in the Depot.

The Sentry Gun is one of the many human technologies adapted by the Combine for their own use after the Seven Hour War. Guns are often deployed by the Combine as static defenses, used to guard areas that are infrequently patrolled, or as a means to supplement a larger defense network already occupied by Overwatch forces. The guns are fitted with small handles and are light enough to pick up and place by hand. When not in use, they are generally stored in small Force Field-equipped lockers.

Despite the similarities with the Sentry Gun, the Combine Sentry Gun has a number of key differences from its predecessor. Mainly, its targeting systems is more sophisticated. It does not rely on laser tripwires, instead incorporating a visual sensor into its main body, allowing to immediately detect intruders in its sight line. Once activated, it will sound an alarm and, after a brief delay, will open fire. Upon losing sight of its target, the gun will scan the area ahead by moving its upper body back and forth, before returning to its inactive state if the target does not reappear after several seconds. This variety of gun also incorporates a limited A.I. which is somehow able to distinguish between Overwatch forces, humans and aliens. Another key difference is that the Combine Sentry Gun has a narrower field of view and range of motion, whereas the Sentry Gun is able to rotate and fire in nearly any direction. The Aperture Science variant has an even more limited field of view.

An individual gun's programming can be accessed and modified remotely through a separate computer terminal when necessary. In ''Half-Life 2''’s chapter 9a, ''Entanglement'', Alyx Vance reprograms a number of Sentry Guns, allowing Gordon Freeman to set them up to protect himself against protracted Overwatch assaults. In ''Episode Two''’s second chapter, ''This Vortal Coil'', Rebels have a supply of reprogrammed Sentries used to repel Antlions.

The Sentry Gun is loaded with the Combine's ubiquitous pulse ammunition, of which it has an essentially limitless supply, although in ''Episode One'', some Combine Ceiling Turret|ceiling-mounted variants with no ammunition remaining are encountered in a Zombie-City 17 Underground|infested underground. 

On the body the alphanumerics "V952" can be seen. It is also featured on other Combine devices.

FileSentry Gun NProspekt 4.jpg|Sentry Gun firing at Antlions in Nova Prospekt.|right|thumb|200px

===''Half-Life 2''===

In ''Half-Life 2'', Sentry Guns are first seen in Nova Prospekt during the chapter Nova Prospekt (Chapter)|of the first name, where the Combine forces make frequent use of them to slow Gordon Freeman's progress and impede the Antlions he takes with him. Later in the game, in the chapter ''Entanglement'' set in the Depot, Alyx Vance reprograms the Turrets so Gordon can use them to protect them while the Combine teleport charges again.

Sentry Guns were also deployed extensively in City 17 after Combine occupation of Earth|the uprising.

===''Half-Life 2 Episode One''===

During ''Episode One'', Sentry Guns are featured in the Hospital, protected by a Force Field and Hoppers, with a metal cabinet holding them in place, making them considerably more dangerous and difficult to defeat.

===''Half-Life 2 Episode Two''===

In the Victory Mine during ''Episode Two''’s second chapter, ''This Vortal Coil'', two Resistance members, Griggs and Sheckley, reprogram two Sentries to ignore them and attack Antlions instead. Bored during their time at the underground outpost, and with nothing else to do, they decorated the Sentry Guns with graffiti and Wikipedianose art|nose art. These guns later prove invaluable in fending off an extended Antlion attack while the Vortigaunts heal a wounded Alyx; however, being damaged and crudely repaired with duct tape and baling wire, they short out and explode in the middle of the attack.

Combine Sentry Guns are also used by the Combine while breaching the White Forest's White Forest 2|secondary silo.

===''Half-Life 2 Survivor''===

In ''Half-Life 2 Survivor'''s battle mode, Sentry Gun is available as a usable item that allows players to place their own Sentry Guns. It is an Battle Points|unlockable item for the Sniper, and is obtained by reaching B-Class. Battle mode's Sentry Guns are team colored for easy identification, friendly Sentries will also have an arrow above them. Engineers can reprogram enemy Sentry Guns by picking them up with the Zero Point Energy Field Manipulator|Gravity Gun.

FileSentry Gun NProspekt 6.jpg|Idle Sentry Guns in Nova Prospekt.|thumb|200px|right

*Sentry Guns cannot be physically destroyed, and must instead be knocked over, which disables them. It can be easily achieved, as it features an unstable tripod base defect that was only noticed after manufacturing. Sentry guns can be taken down by many weapons, however the ease of this, and the weapon best suited to knocking them over, varies depending on the situation. When stood behind them, it is recommendable to use either the Crowbar or Gravity Gun to knock them over, as this uses no ammunition. When at distances, and when they are stood in front of walls, it is easiest to throw Fragmentation Grenade (Half-Life 2)|grenades at them, which can often take out more than one at once. Once knocked over, the Sentry Gun's targeting systems will malfunction and the turret will shoot wildly and sound its alarm for a few seconds before shutting down.

*''Survivor'''s Sentry Guns also explode in short amount of time after being disabled, so it is advised to stay away from them.

*Sentry Guns are powerful enemies but are limited by the simple fact that they can only fire at targets in their sight line and cannot move. When encountered, it is important to consider tactics; the Sentry Gun is immobile, and from behind can be taken down more easily.

*In Nova Prospekt, Gordon has control over Antlions, which can be used as cannon fodder against the Sentry Guns and to distract them while the player runs or sneaks around. If there are enough Antlions, and one or more survives the Sentry Gun's constant shooting, they will attack the Sentry Gun like they would any other enemy and knock it over, thus shutting it down.

*As said above, reprogrammed Sentries come very handy in tough situations. They must be placed at strategic points, where they stand a higher chance of defeating its opponent before it can reach it. When knocked over by Overwatch forces, Sentries must be repositioned as fast as possible. Unlike hostile Sentry Guns, when a reprogrammed Sentry is picked up, it automatically heads upright, which is very convenient during a battle.

*During the chapter ''Entanglement'', it is possible to carry reprogrammed Sentry Guns forward to several areas. First, in cell block D8, where a difficult turret standoff takes place, as many Turrets as possible can be brought from previous areas, which will make the battle much easier. If functional Turret remain after the battle, they can be carried again to the teleportation chamber that follows. One should be careful while doing this, however, since the activated Turrets brought in will shoot at and kill Eli and Mossman. Indeed, reprogrammed Sentry Guns only recognize Gordon Freeman|Gordon and Alyx Vance|Alyx as friendly, and will kill other friendly NPCs.

*It is not possible to get more reprogrammed Sentries via the console, as they are scripted. Any Sentry Guns spawned that way will be hostile towards the player and friendly NPCs.

==Related Achievements==
{|class=wikitable style="vertical-aligncenter;" width=50%
!colspan="2" style="text-alignleft"|''The Orange Box Achievements 2|Half-Life 2''
|rowspan=2 width=64px|FileHl2 beat turretstandoff2.png
!style="text-alignleft"|Warden Freeman (10G)
|''Survive the second turret standoff in Nova Prospekt.''
!colspan="2" style="text-alignleft"|''The Orange Box Achievements 2 Episode Two|Half-Life 2 Episode Two''
|rowspan=2|FileEp2 beat antlioninvasion.png
!style="text-alignleft"|Into the Breach (5G)
|''Help Griggs and Sheckley hold off the Antlion invasion inside the mine shaft.''

==Behind the scenes==
As seen in the model files of the leak|playable ''Half-Life 2'' leak, an unused Sentry Gun model shows it had a some point a different shape. Already a tripod, it was thicker and shorter. The model used in gameplay of the leak is close to the retail model, with some differences.


FileCombine sentry gun leak.jpg|Unused leak Sentry Gun, with temporary textures.
FileCombine sentry gun leak2.jpg|Leak Sentry Gun, close to the final model.
FileCity 17 logo retail.svg|City 17 logo featured on the Sentry bodywork.
FileSentry Gun NProspekt 1.jpg|Sentry Guns in Nova Prospekt.
FileSentry Gun NProspekt 2.jpg|Ditto.
FileSentry Gun NProspekt 5.jpg|Ditto, firing.
FileSentry Gun NProspekt 7.jpg|Ditto.
File2013-02-14 00016.jpg|Idle Sentry Gun in cell block C1.
FileSentry Gun NProspekt 3.jpg|Sentry Gun firing at Antlions in Nova Prospekt.
FileNp kitchens.jpg|Sentry Gun about to be knocked over by Antlions in the Nova Prospekt kitchen.
FileFriendly Turret in storage.jpg|Reprogrammed and ready to use Combine Sentry Guns in a locker in Nova Prospekt.
FileFriendly Turret in storage2.jpg|Ditto. This locker contains 3 reprogrammed Sentry Guns and 3 Supply Crates.
FileFriendly Turret in storage3.jpg|Ditto, after disabling the Force Field.
FileTurret knocked down.jpg|Knocked down hostile Sentry Gun in Nova Prospekt.
FileD3 c17 070001.JPG|Sentry Guns targeting Zombies in a City 17 building. 

===''Half-Life 2 Episode One''===

FileEp1 c17 02a0087.JPG|Sentry Guns protected by bars in the Hospital.
FileSentry Gun Hospital.jpg|Closer look.

===''Half-Life 2 Episode Two''===

FileGround turret rebel 1.jpg|Reprogrammed Sentry Gun model, as seen in the Victory Mine.
FileGround turret rebel 2.jpg|Ditto.
File2013-02-14 00001.jpg|Griggs and Sheckley|Sheckley standing next to a reprogrammed Sentry Gun.
FileTurret antlions mine.jpg|Reprogrammed Sentry Guns firing at Antlions in the Victory Mine.
FileTurret victory mine2.jpg|Ditto.
FileTurret victory mine3.jpg|Ditto, with Griggs on the right.

===''Half-Life 2 Survivor''===

FileSentry Gun HUD Survivor.png|HUD icon.
FileSentry Worldmodel Blue Survivor.png|Model used for unplaced Sentry Guns, held in the player hands. Blue team's version.
FileSentry Worldmodel Red Survivor.png|Ditto, red team.
FileSentry Model Blue Survivor.png|Model used for placed Sentry Guns, blue team's version.
FileSentry Model Red Survivor.png|Ditto, red team.
FileSentry Gun Placed Blue Survivor.jpg|Placed and held Sentry Gun in-game, blue team.
FileSentry Gun Placed Red Survivor.jpg|Ditto, red team.

==List of appearances==
*https// ''Half-Life 2'' at E3 2003 Bugbait {{1st}} {{Nc}}
*''Half-Life 2''
*''Half-Life 2 Raising the Bar''
*''Half-Life 2 Episode One''
*''Half-Life 2 Survivor'' {{Nc}}
*''Half-Life 2 Episode Two''


CategoryHalf-Life 2
CategoryCombine weapons
CategoryHalf-Life 2 Episode One
CategoryHalf-Life 2 Survivor
CategoryHalf-Life 2 Episode Two
CategoryCombine sentry weapons
CategoryPulse weapons