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Basic Concepts
Damage in MWO is tracked using a unitless point system. Weapons do a certain amount of these abstract damage points and items, armor, and the mech’s structure have a number of damage or hit points they can take before being destroyed. Details of this information can be found at 3rd party Web sites like Smurfy’s.
A mech is destroyed when one of the following conditions are met: the mech’s head is destroyed, both of the mech’s legs are destroyed, or the mech’s engine is destroyed (which happens automatically when the center torso is destroyed)..
Items in MWO do not degrade with partial damage--they are either fully functional or destroyed. (There is a slight exception in the case of Clan XL engines, discussed below.)
All damage to a mech is repaired at no cost to the player at the end of each match.
Damage to a mech can have either an external or internal source. The most common form of damage is from external sources, such as weapons fire. Internal damage is generated by exceptional events, such as from an ammo explosion. The difference between the two is that external damage must always destroy any local armor before having a further effect, whereas internal damage ignores armor.
Hit Locations
As discussed in the article on mech customization, mechs have eight sections: the head, center torso, right and left side torsos, right and left arms, and right and left legs. All damage taken by a mech is applied to one or more of these sections. In the case of weapons fire, what section takes damage is determined by where on the 3d model of the mech the weapon actually strikes. There is an excellent post by user Tamerlin that illustrates for most mechs the extent of each section on each mech type.
How Damage is Dealt
When a source of damage (e.g., a weapon) strikes a mech, the section hit takes damage. Some weapons do their full damage instantaneously, others do damage over time as the weapon discharges (Lasers are an example). For damage over time weapons I believe each ‘chunk’ of damage is processed separately by the game. Damage over time fire may be spread across several mech sections depending on the players aim.
Damage to a section is first subtracted from the armor on that section, if any exists. Each point of armor takes one point of damage to destroy. For the head, arms, and legs of a mech there is a single armor pool the damage is subtracted from. For the center, left, and right torsos however, there is a separate allocation of armor to the front and back of the mech. The direction the damage originated from determines whether front or back armor is affected. The destruction of the front or back armor is independent--damaging one does not affect the other and armor on one side only provides protection in that direction.
If armor remains after the incoming damage is applied, there is no further effect, save the loss of armor protection in that section. If the incoming damage exceeds the remaining armor, or there is no armor left, the damage is then applied to the mech’s internal structure.
Internal structure represents the framework or ‘bones’ of the mech, and like armor it has a number of damage points it can take before being destroyed. When the internal structure of a section is destroyed, that mech section is considered destroyed along with anything contained in that section.
MWO doesn’t provide explicit information on the internal structure of mechs, so much of what follows is extrapolated from the BattleTech™ tabletop game (but I think it is accurate).
The number of internal structure points is equal to one half the maximum armor for that section. For example, a Raven can carry 24 armor points on its left arm, and therefore the left arm has 12 internal structure points. (Note to BattleTech players: MWO doubles the amount of armor and internal structure on mechs)
As noted above, if incoming damage exceeds the amount of armor points remaining on the section, the remaining damage is subtracted from the internal structure. Every time damage is done to the internal structure, there is a chance of a critical hit occurring. Critical hits are discussed below. If the incoming damage exceeds the remaining internal structure points, that mech section is destroyed along with all it contains. Any left over damage is transferred on to an adjoining section of the mech, as described in the next section.
During matches the HUD provides a diagram in the lower right corner of the screen representing the general state of armor and internal structure for the various sections of the mech. There is a similar diagram in the top right providing this information for the targeted enemy mech.
Damage Transfer
If a section is destroyed by damage any remaining damage points are transferred to an adjoining section according to the following rules:
- Arms transfer to the adjoining side torso (e.g., right arm transfers to right side torso)
- Legs transfer to the adjoining side torso
- Each side torso transfers to the center torso
- The head (theoretically) transfers to the center torso, but as head destruction kills the mech this is not relevant
- The center torso does not transfer damage--destroying the center torso destroys the mech.
When mech arms are destroyed, they are removed from the 3d model and have no further game effect. Destroyed legs and side torsos, however, remain attached to the 3d model and can be hit by further weapons fire. Damage to these destroyed sections is reduced by 60% and transferred according to the rules above. If the section receiving the transferred damage is also destroyed (as could happen with a destroyed leg transferring to a destroyed side torso), then the damage is further reduced by 80% before being passed to the next eligible section. [ref]
When a side torso is destroyed the attached arm is destroyed as well. This does not trigger any damage effects, such as an ammo explosion, in the lost arm.
Critical Hits
(Attribution note: While most of the info in these guides comes from my own experience, Smurfy’s data file dump, official PGI posts, and the patch notes, the information on the critical hit mechanic is indebted to an excellent post on the subject by user Selfish. Please refer to that article for a more detailed discussion of critical hits.)
Generating Critical Hits
When damage is done to the internal structure of a mech, there is a chance that between one and three critical hits will occur. For most weapons, there is a 58% chance of no critical hit, a 25% chance of triggering one critical hit, a 14% of triggering two critical hits, and a 3% chance of triggering three. Looking at the percentages another way, for normal weapons there is a 42% chance that one or more critical hits will occur--if any critical hits are triggered there is a 60% chance of there being one critical hit, a 33% chance of it being two, and a 7% chance of it being three.
Critical Hit Effects
Critical hits affect items installed in the mech section whose internal structure was damaged. Every item that fits in a critical slot has a number of damage (or hit) points. Critical hit damage subtracts from these damage points and if the damage points of an item are reduced to zero, the item is destroyed. Any excess critical damage above that needed to destroy an item is lost (there is no transfer mechanic for excess critical damage).
Each critical hit does critical damage equal to the total damage potential of the source that damaged the internal structure. So if a weapon does 5 damage points, each critical triggered by that weapon does 5 critical damage. This number is independant from the actual damage done to the internal structure (if our example weapon had to use 3 of its 5 potential damage to destroy the last 3 armor points of a section, 2 points of damage remain to be done to the internal structure but any critical hits will do the full 5 points in critical damage).
Each critical hit (one, two, or three) is treated as a separate critical hit event. For each critical hit event one of the critical slot locations in that section is selected randomly to take the critical hit. Some items are immune to critical hits, currently that includes empty slots, the fixed critical slot items (gyros, actuators, cockpit, etc.), C.A.S.E (see below) and the floating dynamic armor and internal slots created by installing Ferro-Fibrous or Endo-Steel (see the mech customization article for more information). Destroyed items are also immune. These immune critical slot items are not considered when the target of the critical hit is selected. For each critical hit the game selects one critical slot from those eligible to receive it--that means critical slots where items are installed. That item subtracts the critical hit damage from its damage points. [ref]
An example:
Spoiler
Critical Hit Bonus Damage
In addition to the critical hit resolution mechanism described above, each critical hit also does bonus damage to the internal structure of the section equal to 15% of the critical hit damage scored. (So the example 5-damage-point weapon does a bonus .33 damage points every time it critically hits.) This damage is treated as normal damage and will be transferred if the section is destroyed.
Critical Hits and Damage-Over-Time
The discussion above has assumed that all the damage involved in damaging the internal structure was applied at once, as is the case with a Ballistics projectile hit. Many weapons in MWO do their damage over a period of time, Lasers being a good example. For these weapons, the total damage is divided into a number of units that are applied over time for the duration of the weapon discharge (I’d call the units ‘pulses’, but I don’t want to confuse the concept with Pulse Lasers). In total, these units add up to the total damage potential of the weapon. For the purposes of critical hits, each damage unit is treated as a separate weapon strike that does the unit damage. (So if a 10 point damage weapon delivers its damage in ten units of 1 damage each, this weapon’s effect is treated as ten hits by a 1 point damage weapon for the purposes of critical hits.) [ref]
Crit-Seeking Weapons [ref]
Some weapons are more effective at causing critical hits. These are generally referred to a crit-seeking weapons. Currently there are three weapons with this effect: LB-X autocannons, Machine Guns, and Flamers.
Crit-seeking weapons have an increased chance of triggering critical hits--a +14% chance to trigger one critical hit, a +8% to trigger two, and a +3% chance to trigger three (Machine Guns have a lower critical chance bonus of +6%, +3%, and +1% [ref]). Adding this to the normal critical chances means these weapons will cause one or more critical hits 67% of the time they damage internal structure (52% chance for Machine Guns).
Crit-seeking weapons also do more damage when they cause a critical hit.
LB-X autocannons do two times the normal critical damage. As LB-X autocannons do 1 point of damage per pellet, each pellet strike that causes a critical hit does 2 points of critical damage.
Machine Guns do 9.0 times the normal critical damage, or 9.0 x 0.1 = 0.9 points. [ref] [ref]
Flamers do 1.1 times the normal critical damage, or 0.4 x 1.1 = 0.44 points.
Note that this extra damage is critical damage and is done to the items assigned the critical hit, not the internal structure. I do not know if the critical bonus damage applies to the weapons’ raw damage or the improved critical damage.
Finally, as has been noted above, critical hits from weapons fire are only possible when the section struck has no armor. The implication for crit seeking weapons is that they are very dependant on other weapons to destroy the armor on a potential target to maximize the crit seeking weapon’s effectiveness.
Internal Explosions (Ammo and Gauss)
When destroyed (either through critical damage or when the section they are in is destroyed), most items simply cease to function. However, some critical slot items have a chance to explode when destroyed--currently this includes most types of ammo and Gauss rifles. Uniquely for Gauss, the ammo is inert but the weapon can explode.
Ammo has a 10% chance of exploding when destroyed. As mentioned, this can occur by critical damage or when the mech section containing the ammo is completely destroyed. All ammo types have an explosion damage value, usually equal to the damage of one projectile. This explosion damage value is multiplied by the amount of remaining ammo. This can create a staggering amount of damage.
If the ammunition in a critical location has been completely depleted, then no explosion is possible. It will, however, be considered as a possible critical hit location when critical hits are assigned, acting as a buffer. [ref]
Gauss rifles (the weapon not the ammo) is also susceptible to exploding when destroyed. The chances of this happening are high, at 90%, but the damage is less than a typical ammo explosion, causing only 20 points of damage (versus 126 for a ton of LRM ammo).
Explosion damage is considered internal damage and ignores armor. This is true of transferred damage as well (e.g., an ammo explosion that destroys an arm transfers remaining damage to the internal structure of the adjoining side torso, bypassing the side torso armor).
Cellular Ammunition Storage Equipment (C.A.S.E.)
C.A.S.E. is an installable Equipment item that offers some protection from damage transfer when the damage source is internal (e.g., an ammo explosion). C.A.S.E. may only be installed in the left and right torsos. On Inner Sphere mechs, C.A.S.E. takes one critical slot and weighs ½ ton. Clan mechs have the benefits of C.A.S.E. at no cost in weight or critical slots.
When a section of the mech protected by C.A.S.E. is destroyed by internal damage any damage left over, which normally would be transferred to the center torso, is ignored and causes no effect. Note this only happens for internal damage, not external damage, such as weapons fire.
Thus C.A.S.E. acts as a firewall, limiting the impact of a catastrophic internal explosion to the side torso. This has several important implications. First, the side torso and all it contains is destroyed--C.A.S.E. only prevents the damage from passing to the center torso, it does not save the installed section. Second, as the arm is lost when a side torso is destroyed, when C.A.S.E. is triggered the adjoining arm will always be lost.
Probably the most important implication of using C.A.S.E. is its interaction with XL engines. As XL engines are partially installed in the side torso, and the side torso is destroyed when C.A.S.E. is triggered, C.A.S.E. does not protect XL engines from damage. For Inner Sphere mechs the destruction of the side component of the XL engine destroys the engine and thus destroys the mech. Explicitly, C.A.S.E. has no game benefit on Inner Sphere mechs with XL engines. Clan mechs can currently survive the loss of one side of their XL engines but the mechs performance is degraded (the nature of this degradation is in flux currently).
This is one of a series of articles on concepts in MWO. If you found this article helpful, you may wish to read the other articles listed in this post.
Edited by Gauvan, 23 December 2014 - 09:43 AM.
