Following on my discussion of OD&D AC yesterday, here is how to use OD&D attack ranks with the d20 SRD armor system (which uses armor class as target number, also known as ascending AC).

NOTES

Read the table like: clerics of levels 9 through 12 have attained attack rank 3 and have a base attack bonus of +5.

Again we see the power of three at work here. Weak, average, and strong fighting capabilities are enough to distinguish the classes from each other. Other than a category for not progressing at all, I can’t see any finer granularity adding much value to gameplay.

I have capped the progression of the weak and average classes. It should be obvious how to extrapolate the progression if you want it to be unlimited for all classes. I prefer that the pinacle of fighter combat achievement be higher than other classes.

Yes, it’s a table lookup, but it’s offline, not during the game, so who cares?

Simplified d20 SRD armor bonuses:

The really cool thing about this is that there are only 24 different possibilities to remember, and all of them are distinct. So players could potentially use whatever interface they prefer, and it would be all the same to me. So, all are equivalent: I hit plate, or I hit AC 3, or I hit AC 16 (my notes generally use the “AC as plate” form).

The penalty is for ability checks and thief abilities. This is taken directly from the d20 SRD, but the numbers work with the original game, so why not? The movement rates are the same as in this encumbrance system, just presented in a slightly different form.

I’m sure you have seen similar tables to this before, but I include this one here to show the minimum knowledge I need to keep in my head. You’ll also notice that the ascending AC column above is identical to the first OD&D combat rank.

In OD&D, there are only 8 armor classes. AC 9 is the worst (unarmored) and AC 2 is the best (plate & shield). Each number maps reliably back to a given armor type. So, presented with AC 5, you know that means chain armor (or medium armor, if you’re abstracting it).

Probably medium armor, depending on your setting (source)

2. Plate & shield
3. Plate
4. Chain & shield
5. Chain
6. Leather & shield
7. Leather
8. Shield
9. Unarmored

There are no other armor classes in the whole world. If you roll well enough on your starting gold, you can begin at first level with the best armor class in the game (plate armor and a shield cost 60 GP, well below the expected value of 3d6 * 10 starting GP, which is 105 GP). Contrast this with the cost of full plate in Second Edition: 4000 – 10000 GP.

Magic armor does not modify AC, but rather penalizes the attack roll, and the most potent magic armor in Men & Magic is rated +2. By the book, magic shields only help one third of the time, and only if the magical bonus of the shield is greater than that of the armor (i.e., they don’t stack). That requires an extra die roll per combat (extra fiddly), and so will almost certainly be something I jettison. Maybe I’ll house rule magic shields to an additional flat penalty of 1 to the attacker’s roll, along with the full magic bonus for certain saving throws (like dragon breath). I’ve always liked the idea if shields being extra good against dragon breath. [Edit: see here for a clever way from Talysman to handle the shield chance without resorting to another die roll.]

In addition to this form of fixed descending AC, OD&D uses something that I referred to in a previous post as a matrix of combat ranks (my words, not from the book) rather than THAC0 or attack bonus. All classes move through the same ranks, but fighters move through them faster (advancing to the second rank at level 4, when attaining the “hero” title). From Men & Magic, page 19:

Magic-users advance in steps based on five levels/group (1-5, 6-10, etc.), and Clerics in steps based on four levels/group (1-4, 5-8, etc.). Normal men equal 1st level fighters.

I actually like this staggered progression (which is preserved in Moldvay Basic), because it means that PCs need to survive by their wits for a while before they get any mechanical advancement (though I can see why some people might like a smoother progression, and in fact using Target 20 with a smoothly advancing attack bonus seems to be one of the more common OD&D house rules).

Attack Matrix 1

The OD&D approach does have some drawbacks compared to both THAC0 and armor class as target number (more commonly known as ascending armor class). THAC0 is easier to reason with than attack matrices, and direct target numbers don’t require any math (other than situational bonuses and penalties, though in practice those modifiers can end up being rather complicated in 3E).

In the end, all these systems are about the same level of complexity, and all require writing the same amount of numbers on the character sheet. In OD&D, you write down your attack rank column (which is a list of target numbers). In 2E, you write down your THAC0 (and probably derive your other target numbers from that). In 3E, you write your base attack bonus adjusted by all the other modifiers next to every weapon (if you are efficient).

However, the matrix approach does have some benefits, the main one being that anchoring AC helps prevent absurd bonus inflation (especially coupled with the simplicity of ability scores in OD&D). This helps make it clear that while mechanical combat advancement is part of the game, it is not the biggest part of the reward structure. Also, simple AC categories may help make weapon versus AC possible (though you do have to deal with rulings about monster hide being similar to what kind of armor).

This is one reason why I don’t care for the extra d20 SRD armor types that managed to creep into Labyrinth Lord. They break the elegant simplicity of the light, medium, or heavy armor types (modified by a potential shield) present in OD&D and Basic D&D. Obviously there are more types of armor than leather, chain, and plate; however, it does not seem useful to make a distinction regarding armor class past that threefold categorization (other differences can be handled by ruling; for example, chain mail could be used as a crude filter, something that it would be difficult to do with hide armor).

There are some nice firearms rules in the Second Edition AD&D supplement HR4 A Mighty Fortress (see pages 60 and 61).

Here is a summary, for ease of use. Check out the book though, if you have a chance. There are lots of interesting elements contained within.

• Target AC ignores armor (i.e., using newer terminology, is a ranged touch attack); thus, defense against firearms comes from cover and dexterity.
• Exploding damage dice on rolls of 8, 10, and 12 without limit.
• Misfire on a roll of 1 (requires 10 rounds to clean).
• Hanging fire on a roll of 2; this means the shot does not go off, and the fumble range is increased by 1 on subsequent shots until the firearm is cleaned (e.g., after hanging fire once, a misfire happens on a roll of 1 or 2 and hanging fire on 3).
• Fouling (called out as an optional rule): three normal shots count as a hanging shot with regard to misfire and hanging fire chances (to represent the accumulating burned powder.
• Point blank attacks (within 5 feet) inflict +1 burn damage.
• Matchlock firearms: caliver (1d8), arquebus (1d10), musket with rest (1d12).
• Snaplock & flintlock firearms:  pistol (1d8), musket (1d12).
• Wheellock pistols: belt pistol (1d8), horse pistol (1d10).

In the past, I have often just treated firearms like crossbows (that are easier to conceal but make more noise). The HR4 rules suggestions seem reasonable, though, and not overly cumbersome.

My understanding of 3E and 4E initiative is as follows. Each character or monster has an initiative bonus, which is influenced by the dexterity modifier and other situational modifiers (including things like the improved initiative feat). Each character rolls initiative which is 1d20 plus the bonus, and then all characters act in the order of highest to lowest. This is only rolled once, at the beginning of combat, and then the order is followed statically for every following round, and is modified only if characters decide to delay their action (and thus voluntarily place themselves later in the order). Monster initiative is often done as a group, to simplify the referee’s job.

In terms of the math, this type of initiative system is much like achieving surprise: it can benefit you in the first round, but never afterwards. To see why this is, consider a simple initiative order with four entities, acting in the following order: A, B, C, D. Thus, assuming no entity is removed from the combat or delays, the actions would go:

• A, B, C, D, A, B, C, D, A, B, C, D, …

It is clear that A, B, and C have some relative degree of advantage at the beginning of the combat, but after that it is much less clear. For example, the following initiative orders are all also true if ignoring some or all of the first round (as they are all subsequences):

• B, C, D, A
• C, D, A, B
• D, A, B, C

Thus, not much dynamism or potential character advantage is actually gained by using this system, which is relatively cumbersome at the table (all the numbers have to be rolled, written down, and then reordered). Mechanical aids can help; I’ve seen (but never used) magnet systems, smartphone apps, and small whiteboards designed to help with d20 initiative. If you know the initiative bonuses of all combatants beforehand, you could precompile several sample orders, but that seems like a lot of work to me (with little benefit).

Given that, why not just let the character with the highest dexterity go first, and then go around the table? For added impact, seat players around the table in order of dexterity score (or initiative bonus, if you are playing a game that uses such a thing). The referee could use a Holmes-like system and roll 3d6 for monster dexterity at the beginning of combat, and then have a roll-off to determine if the cycle would start with the monsters or the PC with highest dexterity (the advantage here is 2 rolls per combat rather than N rolls, and no need to write down the order or bounce around the table).

For comparison, it is also worth mentioning the AD&D/segment “count up” system, which is similar to, but more elegant than, the d20 system. In the “count up” system, everyone rolls 1d10 and then subtracts their dexterity bonus and adds things like casting times and other penalties. The referee then counts up from one until every entity has acted (thus, lower is better). The advantage here is that weapon speed factors and individual dexterity can contribute to the order of actions without needing to write down an initiative sequence. Since everyone tracks only one single number, it can even be rerolled every turn, so that characters with quick weapons or high dexterity scores will go first more often than not, but nothing is guaranteed (making combat more interesting and less predictable).

It seems to me that the d20 style of initiative is a clear example of a misapplied core mechanic. Roll a d20, higher is always better just doesn’t seem to be convenient for the problem of determining initiative order. I’m probably missing some subtle awesome stuff that can be done with delaying actions in the d20 system. If so, please enlighten me!

Personally, I am quite happy with the Moldvay D&D method of rolling d6 per side every round (I even used that system with Fourth Edition), but I was thinking about this and just wanted to get my thoughts down. The dexterity bonus is only applied to initiative rolls in Moldvay for one on one combats; otherwise, it is a d6 roll unmodified by any character stats.

Here is a quick method for changing how armor works that has been floating around in my head. I don’t claim any originality for this system. It was inspired by Combat Musings over at The Jovial Priest and St. Innocent of Alaska over at Blood of Prokopius.

This assumes a B/X substrate. It would play well with damage by hit die rules, I think.

First, instead of AC there is an evasion score. This is 10 + dexterity mod. This is how hard it is for a character or monster to be hit. You would need to improvise the evasion score for monsters, but I think that should be easy. Sample: goblin, 12; pixie, 17; dragon, 10.

Second, armor provides a damage reduction die. Light (leather) armor is d4, medium (chain) armor is d6, and heavy (plate) armor is d8. If you are wearing armor and take physical damage, you roll your armor die and reduce damage by that much. This is similar to “soak” rules in other games, but I think this implementation integrates nicely with other traditional D&D rules. Monsters also require improv DR scores. Sample: wolf, d4; bear, d6; dragon 2d6.

That’s the core of the system. Here are a few optional rules for added detail.

1. Armor damage. If you ever take a full damage blow (e.g., 4 points from a d4 attack or 6 points from a d6 attack), you roll damage reduction as normal, but mark down a point next to your armor. When N such points have been accumulated (e.g., 8 points for heavy armor), the armor is degraded one step (so degraded plate armor would reduce damage by d6 after one level of degradation). Armor can be repaired, probably at half cost.
2. Weapon versus AC. Using a weapon that is “good against” a particular armor drops the damage reduction die by one step. So, plate armor would only block 1d6 damage from a military pick. Firearms could ignore armor entirely or drop the damage reduction die by one or two steps, depending on how much influence you would like gunpowder to have on your setting.
3. Bulky armor. Armor reduces evasion by one point per class. For example, plate armor would reduce evasion by 3, leather by 1.
4. Armor competency. The damage reduction die is limited by class hit die. So magic-users can wear plate armor, but they still only get d4 damage reduction, and all evasion and encumbrance penalties still apply. Maybe there is some method to gain proficiency with armor for classes other than fighters? That’s beyond the scope of this post, though.

Edit: damage reduction numbers for d6-centric OD&D using 2DTH: light (leather) 2d6 take lowest, medium (chain) 1d6, heavy (plate) 2d6 take highest. Evasion calculated using the B/X dexterity modifier, though it would not apply to anything else.