Sentry Turret
Sentry Turrets are miniature tripod robots that appear in every game in the Portal series. They are seen as incapable of independent movement, but can open each side of their chassis (their 'arms') horizontally in order to reveal two gatling guns. The central part of the chassis holds their red eye, which emits a targeting laser. Almost all of the space within the Turret is devoted to storing the ridiculously stacked ammo, explaining the infinite supply of ammo when firing.
When test subjects are out of sight from the Turret's presence, they will maintain a standby state and will remain motionless with their guns retracted. Moving into their angle of sight however, will cause Turrets to deploy their guns shortly after greeting the unlucky individual before opening fire. They will continue to fire until the target is dead or moves out of sight. If the latter occurs, Turrets will briefly search for the test subject (as indicated by the movement of the targeting laser), after which they will revert to a standby state.
Turrets can be avoided, disabled or destroyed in a number of ways. The most common method is knocking them over, causing them to flail and fire wildly before deactivating. This can be done by picking them up and dropping them, or using any object to tip them over. Additionally, the Discouragement Beamss or Emancipation Grills can be used to completely destroy them.
In Portal, Turrets will shoot glass when the player is on the other side. In Portal 2, however, Turrets will only follow the player behind glass.
Rocket Turret
The Rocket Turret is a unique enemy seen at the end of Portal. It appears as a raw personality core outfitted with a rocket launcher. Upon activation, it will slowly lock onto Chell and emits a sound before firing a rocket. Unlike Sentry turrets, it cannot be disabled or destroyed by the player. It plays a vital role in the battle with GLaDOS, as rockets need to be sent through portals in order to hit her, causing personality cores to detach from her.
Rockets can also be redirected by Chell to shatter the observation windows throughout the offices of the Enrichment Center.
Rocket Turrets used to play a major role in Portal 2, but was later cut.
Defective Turret
Defective Turrets, referred to as "Crap Turrets" by Wheatley, are incomplete, sometimes ammo-less versions of the Sentry Turrets introduced in Portal 2. Unlike normal Sentry Turrets, Defective Turrets have a more humorous and sarcastic dialogue, and speak in a masculine, less robotic voice.
They are harmless to Chell, many times making comments such as "If anyone asks, I killed you". Their voice lines seem to imply they are blind, but they are still aware of Chell's presence. They are first encountered in the chapter, The Escape.
In the game's co-op campaign, the Defective Turrets appear as obstacles for Atlas and P-body throughout the Mobility Gels testing course. These Turrets appear to be as fully functional as regular Sentry Turrets and possesses the innocent and feminine voice tones as they should. The only difference from regular Turrets is that they have been defaced. One Defective Turret in the final test chamber of this test course has been evidently reconfigured by someone, as instead of serving as a typical testing obstacle, before dying it reveals that it "needs to protect the humans".
Frankenturret
Frankenturrets are bizarre Sentry Turret-Weighted Storage Cube hybrids in the single-player campaign of Portal 2. Created by Wheatley in order to complete test chambers when he had no available test subjects, they are first introduced in the chapter, The Itch.
Frankenturrets do not speak, and instead emit incomprehensible chirping sounds. They generally serve as Wheatley's replacement for Storage Cubes once Chell is available as his test subject. Their only difference from normal cubes being that Frankenturrets will hop around aimlessly when it is not placed on a button. When picked up by Chell, they retract their legs inside the cube. If they fall over on their sides or upside down, they will wave their legs trying to get up.
Prima Donna Turret
The Prima Donna Turret (meaning First Woman in Italian, a title given to the lead singer, the diva, in an opera), referred by the game files as the Turret Wife, is a bigger and wider Turret featured at the end of Portal 2's single-player campaign during the Turret Opera, after GLaDOS finally allows Chell her freedom of leaving the Enrichment Center. As its name implies, the Prima Donna Turret provides the lead vocals for the Turret Opera.
Apart from the ending, a Prima Donna Turret can also be found in the chapter The Return, at the end of Test Chamber 11; briefly seen in an elevator just as Chell enters the Chamberlock. It can also be found below the Rattmann's den in the same chapter during Test Chamber 16, where it is observing a turret quartet.
Animal King Turret
The Animal King Turret is a unique type in the single-player campaign of Portal 2 that is only used in an Aperture Science slideshow to represent an "Animal King Takeover" in the chapter, The Courtesy Call. The Turret is considerably colossal in comparison to its Sentry Turret brethren, and appears to operate the 'arms' on its side in exactly the same way.
It can be distinguished from ordinary Turrets by its immense size, crown and leopard skin-detailed chassis. In the context of the slideshow, the Animal King Turret is used as an example of an entity or a form of organization capable of taking control of Earth which "...refuses to, or is incapable of listening to reason".
The Animal King Turret appears only once in the entire game, during the single-player ending sequence when Chell is being brought up to the surface by GLaDOS after defeating Wheatley. It appears to be producing the lower bass tones of the Turret Opera.
Hover Turret
The Hover Turret is an unused Turret found within the game files of Portal 2. It emits a laser, similar to the other types of Turrets, that is coloured light-blue and able to burn the player similar to the burn of the Thermal Discouragement Beam, however unlike the Thermal Discouragement Beam it's laser does not provide a barrier for the player's movement, nor does it interact with game mechanics. The Hover Turret can be spawned within Portal 2 via the cheat command ent_create npc_hover_turret.
