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

Abstract

This essay explains the desire for an alternative BattleMech critical hit resolution method. A basic system using multiple d20 or d10 rolls is outlined with variations for optional increased interior blast effects for larger weapons.

Background

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. 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

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. 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:

Damage	To Hit
1-4	20
5-9	19
10-14	18
15-19	17
20 +	16

Example

An unlucky VND-1AA Vindicator 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 8 missiles hit, 5 to one location 3 to another.

The Large Laser hits the Right Arm, taking out all 5 armor points and 3 internal structure points. That arm has a shoulder, upper and lower arm actuators (but no hand) and a PPC. The Large Laser, having done 8 damage, has a base to hit of 19 on the Critical Hits table. The roll is (in order from top to bottom) {19,9,17,15,20,19}. This damages the shoulder and hits the PPC twice. In addition, since the arm received 3 critical hits it is blown off.

The LRM 10 happens to hit Left arm, which was damaged in a previous round, with 5 points and then hits the left arm again with 3 points. Of the first salvo 4 damage is done to the armor and 1 to the internal structure. Doing 5 points of damage the base to hit on the critical table is 19. With a full set of actuators and a small laser the roll is {13,19,4,10,11}. This hits the upper arm actuator only. The 3 points from the second group also roll for critical, but since this is only a 3 point group, the base to hit is 20. As the upper arm actuator was hit previously, it need not be re rolled. The roll is {6,15,5,2} resulting in no critical hits.

The AC/20 hits the center torso doing 12 damage to the armor and 8 to the structure. Being a 20 point weapon, the critical base to hit is 16. As this is a big roll, the player decides to roll the 6 engine dice and gets a result of {10,2,19,6,15,18}, causing 2 engine hits. Then he rolls the 4 gyro dice with a result of {4,17,12,7} for a single gyro hit. Lastly he rolls the 2 other slots, rolling a 4 and a 7 for no hits. If the player had 6 dice of one colour, 4 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 MG is rolled, hitting the Left Torso, Critical. The LT has 2 heat sinks, an LRM-5 and one section of LRM-5 ammo. The MG has a critical to-hit of 20. Amazingly he rolls {20,20,20,4} which takes out two heat sinks, the LRM launcher but amazingly misses the ammo.

Severely battered, having lost one arm and most of its arsenal and with an almost destroyed engine and gyro the Vindicator nonetheless still able to walk away....