Basic combat rules
Combat generally begins with a surprise turn, where the initiator of combat takes an action and his target gets to respond. Regular combat rules follow.
First off, the game determines who gets to go first. This depends on each character's sequence. The rule here is simple: a higher sequence goes first.
When it is your turn, and you choose to take action, the game determines if you even have time in that turn to take your action. SPECIAL uses Action Points (APs) to work this out. Each action you can take in combat has a particular cost in APs. If your current number of remaining APs is equal to or greater than the cost of your action, you can do what you have in mind. A character's maximum APs are determined by Agility. Most attacks cost 5 APs by default, though with different weapons, modes of attacks and combinations of perks, this can change. Movement costs one AP per hex moved.
- Example: Joe the Raider is in a bar brawl. He wants to slug the barfly next to him. A solid punch costs 2 APs. Joe currently has 8 APs. He has more than enough APs to do what he has in mind and takes a swing.
It is not enough to decide to attack. You actually have to connect before anything interesting happens. In essence, the target's chance of avoiding the attack is subtracted from your chance of successfully attacking. The resulting percentage is rolled against to determine whether you've successfully hit. Your chance of successfully attacking is mostly due to your skill with whatever sort of weapon you're using, modified by attributes (like Strength or Agility) or perks. Your target's chance of avoiding the attack is mostly due to their Armor Class, which is determined by their Agility and the armor they are wearing. Additional bonuses or penalties to the attack can apply based on other conditions such as the range at which you attack or the lighting.
- Example: Joe the Raider attacks a farmer. Joe has trained hard with his spear and has a total skill of 89% with melee weapons. The farmer's he's attacking is just wearing his threadbare clothing and thus only has the Armor Class afforded by his average agility: 5. It's a bright, sunny day and Joe is attacking in melee, so no other special conditions apply. Joe's chance of hitting is calculated as follows:
- 89% (attacker's weapon skill) - 5% (defender's Armor Class) = 84%
- Joe has an 84% chance of successfully skewering his target. The farmer is likely toast.
Once an attack has been confirmed to be successful, damage must be determined. First, the raw damage is rolled. This is determined by the damage range of the weapon or hand to hand attack being used. Each weapon does more or less damage than any other. A slap from a 90-pound weakling hardly hurts at all, but a point-blank shot from a combat shotgun is painful. For melee and hand to hand attacks, the damage is modified by strength. Certain feats also can modify attack damage. Different types of ammunition can also have different effects on damage, depending on the Damage Modifier (DM) of the ammunition.
Once the raw damage has been determined, the target's armor comes into play again. First, the armor's Damage Threshold (DT) is applied. This is a fixed number of points of damage that is directly subtracted from the attack's damage. Next, a percentage equal to the armor's damage resistance (DR) is removed from the remaining damage, eventually modified by the Damage Resistance Modifier (DRM) of ammunition. Each armor has one Armor Class but has different DTs and DRs for different types of damage. See Damage for information on damage types.
- Example: Joe stabs a caravan guard with his spear. The weapon's base damage is 3-10. Joe's strength gets him an extra 2 points of damage. He ends up with a solid blow for 9 points of damage. The caravan guard is wearing a leather jacket. A spear stab is normal damage, so those statistics are used. Unfortunately, the frail leather jacket has 0 damage threshold, so nothing is subtracted from the damage. It does, however, have 20% damage resistance to normal. The damage of 9 undergoes a reduction of 0.2 x 9 = 1.8 rounded down to 1. Thus the guard takes 9 - 1 = 8 HP of damage and readies his sledgehammer to take a swing at Joe.
The final damage caused by a ranged weapon can be computed by the following formula:
(final damage) = (( raw damage * DM ) - DT) - RoundDown((DR + DRM) * ((raw damage * DM) - DT)))
- raw damage is the rolled damage into the damage range of the weapon
- DM is the Damage Modifier of the used ammunition
- DT is the Damage Threshold of the target's armor
- DR is the Damage Resistance of the target's armor
- DRM is the Damage Resistance Modifier of the used ammunition
If the player has the Living Anatomy perk, 5 HP of damage is added after everything else.
- Example: Joe shoots a combat-armored caravan guard with his .44 magnum revolver. The armor has 5 DT and 40% DR. The gun has a base damage of 12-18. .44 magnum JHP has DM 2/1 and DRM 20. Joe rolls 14 base damage. This is doubled to 28 by the ammunition's DM. The armor's DT then subtracts 5, so 23 remains. This remainder undergoes a reduction of (40% + 20%) * 23 = 13.8, which is rounded down to 13. The guard takes 23 - 13 = 10 damage and readies his H&K CAWS to blow Joe's brains out.
Note: The Fallout 1 engine does not implement the ammo modifiers, so in that game there is no difference between JHP and AP ammo. (explanation thread)
Taking too much damage will typically result in death. Characters have a derived statistic called Hit Points that represent how much damage they can take before they die. If you take damage equal to or greater than your hit points, you are dead, which is a shame.
Some weapons have several different ways to attack aside from a single shot or a jab.
First, every weapon (except burst-only weapons) allows you to make an Aimed Shot (provided you don't have the Fast Shot trait). Aimed shots allow you to aim for a particular part of a target's body. Aiming for limbs gives a chance to cripple the limb, which has several penalties. Aiming for the groin, head, and especially eyes significantly increase the chance for a critical hit, but makes for a correspondingly more difficult shot.
Many ranged weapons will allow you to make a Burst Shot. When you burst, you fire more bullets in less time. Different weapons will allow you to use more or less rounds in one burst, but the idea is generally the same: put more bullets in the air. The advantages of burst shots are that you can either hit one target for far more damage (if multiple rounds hit and especially if several rounds achieve critical hits) or hit several targets at once as bursts fire in a cone. The downside is that bursts are more expensive in both ammunition and action points and may not necessarily be worth the expenditure. A further problem is that a burst shot may hit an unintended target(s), like your party members or neutral characters.
Some melee weapons have different attack options (jab, swing, etc) and some, like the spear, has a throw option, which gives melee weapons a bit more range.
Ranged Combat is first determined by your skill for the specific ranged weapons you are using. The Base to Hit (BTH) is the result of your skill -30%. In addition, you add 8% or 16% (dependent on the maximum range of the weapon) for each point of Perception - 2, natural or modified by special perks and traits like sharpshooter or Night Person to your BTH. Subtract 4% for each hex distance between you and your target. You can also call an Aimed Shot, which also modifies your BTH according to the area you want to hit. In darkness also subtract an additional 10% if you are more than 4 hexes away from your target. Keep in mind if you miss there is a slight chance to hit another target.
- BTH = (Skill - 30) + ((PE - 2) * 16) - (HEX * 4) - (AC of Target) [- 10% at night if HEX >= 5] for all rifles rifles from FO1 with a range >25
If you reach a BTH of 0 or below it is not possible to hit the target.
Some weapon-classes also affect your BTH. Shotguns for example raise your BTH by 20% if you are >=4 and even by 30% if you are >=5 hexes away from your target, while at the same time the damage done by the weapon is reduced.
Sniper-Weapons like the hunting rifle can fire in the first 10 hexes away from your target with +4% to the BTH and without any distance modifiers. For example, your BTH is usually 55%. While using the hunting rifle, you get initially +4% to your BTH. You are 8 hexes away, so your BTW is still 59%. Beginning with the 11th hex distance between you and your target, each hex subtracts 4% of your BTH as usual. In the example, instead of being 8 hexes away, you are 12 hexes away, your BTH is reduced to 47%.
There are also special unique weapon modifiers like +20% BTH for the 9mm Mauser because it is "extremely accurate".
If an attacker is lucky, he may find that his attack is particularly painful for the target, potentially causing crippled limbs, damaged eyesight, or even instant death. These are Critical Hits. When you make an attack, a derived statistic called critical chance is checked against to see if your attacking is critical. If it is, a random effect follows, which can be extra damage or more drastic outcomes.
On the flip side, there are also critical failures. If you really fumble your attack (characters with the Jinxed trait are notorious for this), something disastrous may occur. The most common result is attacking the wrong target (for instance, you may be aiming at a mutant, but you will accidentally shoot your friend who is in between you and the mutant). Other possible results include weapon jams, dropping weapons, weapon destruction, causing damage to oneself (by stabbing yourself in the foot or some such), and other unfortunate outcomes.