VATS

The Vault-Tec Assisted Targeting System, or V.A.T.S., is a queuing system for Fallout 3 and Fallout: New Vegas, inspired partly by the ability to shoot specific body parts in the turn-based combat system of Fallout and Fallout 2.

While using V.A.T.S., the otherwise real-time combat is paused. Various actions cost action points, and both the player and enemies can target specific body areas for attacks, inflicting specific injuries.

When using V.A.T.S. against a humanoid enemy, there are generally seven different areas that are targetable; the head, torso, left arm, right arm, currently held weapon, left leg, and right leg. However, there may be other points available when specifically facing off non-humanoid creatures (e.g. robot combat inhibitors, ant antennae).

When targeting a part, the screen displays a percentage of how likely the attack will hit the targeted area based on distance from the target, visibility of the targeted body part, and combat skill. A higher percentage does not equate to more damage done; for example, an 80% hit to the head/sensors will likely do more damage than a 95% hit to an armored torso. The readout also displays the overall condition of the body parts on the target.

V.A.T.S. also displays a health meter indicating the target's overall health, as well as an indicator showing the amount of damage a V.A.T.S. attack round using the player's current weapon will inflict. Note that the indicator shows the weapon's maximum noncritical potential damage that the weapon would do if the player's relevant combat skill (i.e. Small Guns) were at 100. If the player's combat skill is less than 100, they will do less real damage with each attack than what the V.A.T.S. indicator shows. On the other hand, achieving a critical hit (such as a Sneak Attack Critical) can potentially produce more real damage than the indicator shows.

There is a 15% boost in the chance for a critical hit in V.A.T.S. mode. Certain perks can improve this boost (multiplicatively).

Unlike previous Fallout games, it is not possible to target the eyes or groin nor target any individual body parts in melee and unarmed combat, however you will still strike specific limbs without aiming for them, and you can still cripple and dismember enemies. Also unlike the previous games, you can't target children.

Effects
Although body part damage can be achieved through manual aiming, V.A.T.S. allows more effective targeting of particular body parts. The effects of crippling specific body parts is listed below.
 * Crippling the head will reduce overall accuracy and perception (-4) of the target. If inflicted upon the player, the screen will intermittently get fuzzy and a ring will be heard through the speakers, loosely simulating the effects of a concussion.
 * Crippling the torso will result in the target flinching far more often from shots than normal. This can also affect the player throwing off aim and stopping your attacks momentarily.
 * Crippling an arm will result in any weapon reliant on that arm for holding to be dropped, and will also drastically reduce accuracy. This is particularly evident when the player uses a scoped weapon such as a Sniper Rifle. The weapon itself is not destroyed, and they will likely just pick it back up again.
 * Crippling a leg will result in impaired mobility. Creatures who rely on leaping attacks (e.g. deathclaws) will no longer be able to use them.
 * Crippling the held weapon will ruin it and make it unusable, and/or send it flying out of the target's hand. Although the condition is zero and it can't be used, it can still be collected and repaired, or used for repairs. The player's weapon may be damaged by enemy fire as well. If the player's weapon CND reaches 0, it will be unequipped as opposed to flying out of the player's hands. If it is an explosive ordinance (like a frag grenade), it will explode, dealing its damage to the target holding it (and any others nearby). Grenades can be targeted by V.A.T.S. while in the air after being thrown as well; As long as the game isn't updated. The 1.4 update (or later) removes the ability to target "en-route" grenades and missiles.
 * Some enemies have alternate targets: Robots, ants, and others have special targetable parts that when crippled will push them into a frenzied state, where they no longer discern between friend and foe and attack anything.

Crippling any body part will result in the target momentarily pausing to clutch the now crippled body part or reel from the injury. Specific body parts cannot be targeted when using thrown explosives or melee/unarmed weapons in V.A.T.S..

Related perks

 * Action Boy
 * Commando
 * Concentrated Fire
 * Grim Reaper's Sprint
 * Gunslinger
 * Mysterious Stranger
 * Nerves of Steel
 * Paralyzing Palm
 * Sniper
 * Wired Reflexes

Glitches

 * The 1.1.035 patch heavily bugs the V.A.T.S. system. There is now often a noticeable pause when activating V.A.T.S., especially so when Anti-Aliasing is enabled. Furthermore, any perks that modify the To-Hit chance in V.A.T.S. (like Gunslinger or Commando) have no effect and are essentially useless until the bug is patched. Grenades and rockets now have 0% chance to hit when targeted while in flight, and there are frequent miscalculations (such as all body parts having 0% to hit when they shouldn't). These are NOT fixable by PC users via G.E.C.K. editing, as these values depend on the game's EXE file, something which naturally can only be patched by Bethesda. Patch 1.5 has fixed the broken To-Hit perks; however, it does not resolve the pause bug (but does reduce it for some players) nor fix occasionally-wrong accuracy calculations, and projectiles in-flight are still un-hittable.
 * The paused framerate and screwy hit percentages can be fixed for a moderate drop in the maximum attainable framerate by use of a mod called the Fallout Stutter Remover (which requires a minimum version of FOSE Beta 1.2). The default framerate cap for the FSR is 30, but can be increased by altering settings in the mod's associated INI. It is not known yet if the un-hittable grenades are also fixed.


 * Sometimes, when the player opens V.A.T.S. and the targeted enemy walks behind a corner, you won't be able to move until your enemy is dead. What it comes down to is that your followers need to kill the enemy for V.A.T.S. to close, which might take a LONG time since everything is in slow motion. In some known occurrences(xbox360), this resulted in the death of Dogmeat and the other follower that was accompanying the PC, which in turn allowed the target to live, and forcing the player to reload a previous game due to not being able to close V.A.T.S. mode.


 * Update: On the Xbox 360 version, it is not possible to recover from this glitch by holding down the Xbox menu button until the standard V.A.T.S. target selection re-initiates


 * Occasionally V.A.T.S. will let players see through walls or rocks.


 * When playing in first person mode, and lining up a shot which is only a few degrees above or below an obstruction, even though you appear to have a clear shot, in V.A.T.S mode, your shots will sometimes hit the obstruction every time. Apparently there is sometimes a slight position difference between first person and V.A.T.S.. This can also sometimes occur in free aim if the obstruction is in front of you (e.g. sandbags) and your weapon appears to be pointing above it.


 * If you target an enemy in V.A.T.S. too quickly after turning, you may have 0% chance to hit the enemy at all until you exit V.A.T.S. and reenter.
 * Similarly, if one's eyes are literally inside the target (so one can see straight through it and see the bits of texture that colour the target), you will have 0% chance to hit any part of the target's body.


 * If you take the Mysterious Stranger perk, use the Sniper Rifle in V.A.T.S. and he appears, it causes the game to crash often. So avoid using this weapon in V.A.T.S. mode. This is ill-advised at any rate, since using the weapon in V.A.T.S. will make the already fragile weapon degrade even faster, as well as forfeit the accuracy bonus you would get using the scope.


 * Using V.A.T.S. with Unarmed or Melee Weapons can reveal a few bugs:
 * The hitboxes of both types of weapons seem to increase and move away from the weapon. This is evident when targeting a fleeing enemy: the target may be well out of regular range when the Lone Wanderer swings his or her weapon, yet has a chance to take damage. Likewise, being right up against an enemy will sometimes give a hit percentage of 0. This seems to suggest that both types of weapon have a minimum range in V.A.T.S..
 * Sometimes, after accepting the attack sequence, the player may just stand with his or her weapon drawn for the duration of what would have been a normal attack sequence. This doesn't spend AP however, so it is mildly annoying. It can become an issue when fighting groups of enemies, because they have the chance to (slowly) surround the player, making battle difficult.
 * The V.A.T.S. hit percentage for Melee Weapons and Unarmed weapons is very different from ranged weapons. For example, if the player enters V.A.T.S. with two targets equidistant and in range of the player, yet one is behind the player when V.A.T.S. was activated, the target behind the player will display a 0% chance to hit. This happens occasionally with ranged weapons as well, but not as often due to their range.


 * When the Player starts an attack in V.A.T.S. the game may freeze but the sound of the attack and the radio station can still be heard but after the sound has stopped playing no other sounds will play until the game is restarted. This can be very annoying if the player has not saved or auto-saved in a while.
 * Don't use V.A.T.S. when an NPC walks into an area that needs to be loaded. It'll freeze your game.


 * Sometimes, V.A.T.S. will occasionally freeze to where you are only able to switch between enemies and body parts. The Select, Accept, and Return are all disabled.
 * Also the game doesn't allow you to access the main menu by pressing Start, forcing the player to eject the disk or shut down his console (Confirm no Start button function - 360)

Videos
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V.A.T.S. V.A.T.S.