User:LRichardson/A Proposed Alternative to BattleTech Critical Hit Resolution

Emblem-important.svg Not Canon!
The subject of this article does not contribute canonical content to the BattleTech universe, either because it is not intended to or because it is not an official product.
See the article's section on Canonicity for details.

Authors Note: This essay is a fan made derivative work and is not a canonical rule. While compatible with BattleTech as published it is obviously unsuitable for tournament use.


This essay explains the desire for an alternative BattleMech critical hit resolution method at the Total Warfare scale of play. A basic system using multiple d20, d10 or d6 rolls is outlined with allowance for optional increased interior blast effects for larger weapons. Advantages of this system are speed of resolution and variability of lethality between weapons.


The canonical critical hit resolution system presented in Total Warfare process is meant to randomly distribute critical hits among the equipment listed in a given 'Mech hit location. The traditional process is that once an internal hit has been recorded a roll of 2d6 is made to determine how many critical hits occur, 1d6 is rolled twice to determine the specific slot that each individual critical hit is applied to. If the rolled location is empty or contains certain types of equipment the location is re rolled until a valid location is selected. While satisfactory for most simple games, the method is time consuming and, in larger BattleTech scale battles, can lead to significant delays to the game.

Another complaint that comes with the canonical critical hit resolution is that the more stuff that is in a given location to be hit the less likely any given item will be destroyed. The issue with this is that if a blast occurs in a small area then it can be argued that the more things that there are there to get hit the more things in total are likely to get hit. That is to say that if one were to briefly spray a hose at a packed grandstand more people are going to get wet than if the stands were only half full. There are significant counterpoints to this line of thinking, but this essay assumes that the more-things-to-hit position is preferable to model.

An alternative method to reduce the time needed to generate critical hits then ought to:

  • reduce the total number of rolls needed,
  • reduce the number of steps required
  • eliminate the need to re-roll invalid hit locations and
  • make the odds of a given location being damaged be independent of the total list of equipment present.

For the widest audience such a system would preferably not alter the lethality of the game to any great degree. Similarly the general probabilistic damage patterns should more or less be consistent with the canonical game.

The basic Critical Hits Table rolls 2d6 and lists the total number of critical hits to apply[1]. A method of eliminating this step would be to resolve each hit location individually rather than determine the number then location of each hit. A likely complaint to this line of thinking is that this requires an individual roll for each hit location filled on the chart rather than a single roll to determine the number hit. This problem however is less significant than initial appearances would suggest. If each locations roll is resolved on a single die all of the hit locations affected can be rolled simultaneously. For example, if a critical hit were being made against the center torso, a cup containing six green dice (representing the engine), four red dice (the gyro), one white die and one black die (the two remaining slots in the center torso, if filled) could be rolled all at once. Dice exceeding a certain threshold would then be picked up and counted by colour and those would be counted as critical hits. While this does not indicate which of the slots for a given item are hit, Total Warfare itself does not discriminate between which of an items hit locations are hit compared to the effect of that hit. That is to say an engine hit is an engine hit; it does not matter if the first engine slot or the last is marked off, only the total number of hits matters.

The probability calculation associated with this kind of roll is the binomial distribution. This happens to display similar characteristics to the results of the canonical method. At this point the only things left to decide are the kind of dice to use and the base-to-hit number for the roll. The three most likely candidates to suggest would be 1d6, 1d10 and 1d20 as each of these sizes are commonly available in sets. That said, any single die would be satisfactory to many. The adjustment of the base-to-hit number also allows for differences in blast effects between different weapons.

Basic Rule[edit]

The d20 is the "common" polyhedral die that has the highest resolution and will be used for this rule. This rule also provides for greater lethality of larger weapons.

When a BattleMech location has been hit in a manner that calls for a critical hit to be resolved, roll 1d20 per each critical slot filled in that location. The base to hit is based upon the amount of total damage the weapon inflicted on that hit location. This is a "save" roll, that is to say that if the number rolled on the die is equal to or less than the target number the location is hit. For example, treat each 5 point LRM location result as a single 5 point weapon while an AC/20 is a 20 point weapon. If the location is a limb and the result is 3 or more critical hits in that one hit, the limb is blown off.

Critical Base to Hit Table[edit]

Damage To Hit
1-4 1
5-9 2
10-14 3
15-19 4
20 + 5


An unlucky VND-1AA Vindicator[2] is mugged in a dark alley by an assault Mech that hits with an LRM 10, a Large Laser, an AC/20 and a machine gun. The LRM 10 rolls eight missiles hit, five to one location three to another.

The Large Laser hits the Right Arm, taking out all five armor points and three internal structure points. That arm has a shoulder, upper and lower arm actuators (but no hand) and a PPC. The Large Laser, having done eight damage, has a base to hit of two on the Critical Hits table. The roll is (in order from top to bottom) {2,9,17,15,1,2}. This damages the shoulder and hits the PPC twice. In addition, since the arm received three critical hits it is blown off.

The LRM 10 happens to hit Left arm, which was damaged in a previous round, with five points and then hits the left arm again with three points. Of the first salvo four damage is done to the armor and one to the internal structure. Doing five points of damage the base to hit on the critical table is two. With a full set of actuators and a small laser the roll is {13,2,4,10,11}. This hits the upper arm actuator only. The three points from the second group also roll for critical, but since this is only a three point group, the base to hit is one. As the upper arm actuator was hit previously, it need not be re rolled. The roll is {6,15,5,1} resulting in one critical hit to the small laser.

The AC/20 hits the center torso doing twelve damage to the armor and eight to the structure. Being a twenty point weapon, the critical base to hit is five. As this is a big roll, the player decides to roll the six engine dice and gets a result of {10,6,5,16,15,3}, causing 2 engine hits. Then he rolls the four gyro dice with a result of {4,17,12,7} for a single gyro hit. Lastly he rolls the two other slots, rolling a nine and a seven for no hits. If the player had six dice of one colour, four of another and one each of two other colours he could have rolled this result all in one throw with no change in the odds.

Lastly the machine gun is rolled, hitting the Left Torso, Critical. The LT has two heat sinks, an LRM-5 and one section of LRM-5 ammo. The machine gun has a critical to-hit of one. Amazingly he rolls {1,1,1,4} which takes out two heat sinks, the LRM launcher but misses the ammo.

Having an almost destroyed engine and gyro, a blown off arm and most of its arsenal destroyed, the severely battered Vindicator nonetheless is still able to walk away....

Other Notes[edit]

If a die with a lower number of faces, such as a d6 or d10, is to be used then the modifiers for the amount of damage the weapon causes should either be altered or, if desired, left as is and simply accept the much higher lethality. That is to say rolling over five on a ten sided die is a lot less likely than rolling over five on a twenty sided die. It is worth noting that the increased likelihood of critical hits from a large weapon such as a Gauss Rifle or AC/20 means that such weapons are made much more useful than they traditionally have been in Total Warfare[3]. Since many consider the AC's to be underpowered for their mass and size, this could be seen as something of a balancing point to justify the number of canonical units that are equipped with such weapons. Left up to the reader is the exercise of whether it is better for a locations structure to be hit with four five-point groups or one twenty-point hit. Along this same line this also allows for an additional attribute to be added to the weapons table: a modifier to the base to hit number separate from the weapons damage.

This critical hit resolution method does have a problem in relation to mech design. Some `Mechs are designed with a distribution of equipment in locations intended to protect critical items. For example, stuffing machine guns and such in a location that has an ammo bin so that any critical hits rolled are likely to be absorbed by something other than the ammo. The proposed critical hit system in this writing makes a given location equally likely to be hit if it is the only item in the location or if it is only one of twelve items in the location. This has the effect of making items like Anti Spalling Buffers useless.

Some credit for this concept should be given to Avalon Hill. A system very much like the one described here was used in the vehicle hit system in the 1984 game "Firepower", an infantry scale contemporary man to man combat game and formed the inspiration for this rule-set.


  1. Total Warfare, p. 124
  2. Record Sheets: 3039, p. 115
  3. Tech Manual, p. 208


External Links[edit]

Avalon Hill's "Firepower"