Combine Sentry Gun

Combine Sentry Gun
Production information
Faction	Combine
Type	Autonomous pulse sentry gun platform
Technical specifications
Damage	3 (per bullet)
Ammo type	Pulse ammunition
Rate of fire	High
Projectile speed	Fast
Accuracy	Medium
Range	long
Usage
Used by	Combine Soldiers; Alyx Vance; Gordon Freeman; Rebels;
Counterweapon(s)	Gravity Gun; Grenades;
Game information
Entity	npc_turret_floor (HL2); npc_sentrygun_mp (Survivor);

"I can reprogram these turrets to attack the enemy. You set them up to defend the control room."

― Alyx Vance^[src]

The Combine Sentry Gun,^[1] also known as the 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. It is commonly used by the Combine to guard chokepoints and vital areas. In terms of gameplay, it is the successor of the Sentry Gun featured in Half-Life and its expansions, and the predecessor of the Sentry Turret of the Portal series. In Half-Life: Alyx a few of them can also be glimpsed. The Sentry Gun is also available in the battle mode of the spinoff game Half-Life 2: Survivor as a placeable item.

Overview[edit]

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. Sentries are often deployed by the Combine as fixed defenses, used to guard areas that are infrequently patrolled or as a means to supplement larger defense networks already occupied by Overwatch forces. They are loaded with the Combine's ubiquitous pulse ammunition, of which they have a seemingly limitless supply, although in Episode Two, certain Sentry Guns are scripted to act as if they ran out of ammunition. The guns are fitted with small handles and are light enough to be picked up and placed by hand. When not in use, they are generally stored in small lockers equipped with Force Fields. On the Sentrys' body the alphanumeric "V952" can be seen. It is also featured on other Combine devices.

Despite the similarities with the HECU Sentry Gun, the Combine Sentry Gun has a number of key differences from its predecessor. Its targeting system is more sophisticated and does not rely on laser tripwires to activate, instead incorporating a visual sensor into its main body, allowing it to immediately detect intruders in its sight line. Once activated, it will sound an alarm and open fire after a brief delay. Upon losing sight of its target, the gun will scan the area ahead by turning its upper body back and forth before returning to its inactive state after several seconds. Sentry Guns also seem to incorporate a limited A.I. which is somehow able to distinguish between Overwatch forces, humans, and aliens. Another 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.

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 the duo against protracted Overwatch assaults. In Episode Two’s second chapter, This Vortal Coil, Griggs and Sheckley have two reprogrammed Sentries used to repel Antlions.

Appearances[edit]

Sentry Gun firing at Antlions in Nova Prospekt.

Half-Life 2[edit]

In Half-Life 2, Sentry Guns are first seen in Nova Prospekt during the chapter of the first name, where the Combine forces make frequent use of them to slow Gordon'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 the uprising.

Half-Life 2: Episode One[edit]

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

Half-Life 2: Episode Two[edit]

In the Victory Mine during the chapter This Vortal Coil, two Resistance members, Griggs and Sheckley, reprogrammed two Sentries to ignore them and only attack Antlions instead. Bored during their time at the underground outpost, they decorated the Sentry Guns with graffiti and nose art. These guns prove invaluable in fending off an extended Antlion attack from multiple directions; however, being damaged and crudely repaired with duct tape and baling wire, they short out and explode in the middle of the attack.

Another Combine Sentry Gun can be found in the junkyard, guarding the Combine Autogun. If still active after the Autogun is destroyed, this Sentry Gun will appear to be out of ammunition. A Sentry Gun guards the Force Field-generating machinery near the White Forest Inn and must be knocked over in order to access the Power Generator. Similarly to the previous instance, the Sentry Gun will appear empty if placed upright again.

Several Combine Sentry Guns are used by the Combine while breaching the White Forest's secondary silo. All of them spontaneously short out and explode when the player reaches the silo's entrance, presumably to avoid interrupting scripted sequences with friendly NPCs.

Half-Life: Alyx[edit]

A few Sentry Guns are seen shooting at Antlions at the entrance of the Central Zoo. However, Alyx does not directly battle any Sentry Guns during her journey to the Vault.

Half-Life 2: Survivor[edit]

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 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 Gravity Gun.

Tactics[edit]

Idle Sentry Guns in Nova Prospekt.

Sentry Guns are powerful enemies but are limited by the fact that they can only fire at targets in their sightline and cannot move. They 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 that was only noticed after manufacturing.^[1] Sentry guns can be taken down by many weapons, however, how easy this is and what weapon is suitable varies depending on the situation. When standing behind them, it is recommendable to use either the Gravity Gun to knock them over or simply pick them up and throw them down, as this saves ammunition. When at distances or confronting Sentries placed against walls, it is easiest to throw grenades at them, which can often take out more than one of them 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.

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 and knock it over.

As said above, reprogrammed Sentries come in very handy in tough situations. They must be placed at strategic points, where they stand a higher chance of defeating their opponent. When knocked over by enemies, 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 Turrets 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, preventing further progress without displaying a game over screen. Reprogrammed Sentry Guns only recognize Gordon and Alyx as friendly, and will kill any other friendly NPC.

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

Related Achievements[edit]

Half-Life 2
	Warden Freeman (10G)
	Survive the second turret standoff in Nova Prospekt.
Half-Life 2: Episode Two
	Into the Breach (5G)
	Help Griggs and Sheckley hold off the Antlion invasion inside the mine shaft.

Behind the scenes[edit]

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

Cut male citizen voice lines in the playable Half-Life 2 leak files reveals that Rebels were originally intended to verbally call out turrets like other enemies they can encounter.

Trivia[edit]

On a surveillance screen in Nova Prospekt, Combine Soldiers can be observed carrying Sentries on their shoulders and deploying them manually.