VATS

The Vault-Tec Assisted Targeting System, or V.A.T.S., is a queuing system for Fallout 3, 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.

There is a 15% boost in the chance for a critical hit in VATS.

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.

Effects
Although body part damage can be achieved through manual aiming, VATS 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 of the target. If inflicted upon the player, the screen will intermittently get fuzzy and a ring will be heard through the speakers, 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 will fly 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 VATS while in the air after being thrown as well.
 * 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. Specific body parts cannot be targeted when using thrown explosives or melee/unarmed weapons in VATS.

Glitches

 * The 1.1.035 patch heavily bugs the VATS system. There is now often a noticeable pause when activating VATS, especially so when Anti-Aliasing is enabled.  Furthermore, any perks that modify the To-Hit chance in VATS (like Gunslinger or Commando) have no effect and are essentially useless until the bug is patched.  It is likely a patch related to hardcoded systems, so PC users with GECK will likely be unable to solve it; a new official patch will be needed.  The recent 1.4 patch offers no such fix, so the issue is still outstanding.


 * Sometimes, when the player opens VATS 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 VATS 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 VATS.


 * 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 VATS target selection re-initiates


 * Occasionaly 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.


 * 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.


 * 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


 * Using V.A.T.S. with Unarmed or Melee Weapons can reveal a few bugs:


 * The hitboxes of both types of weapons seem to largen 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.

V.A.T.S.