Reasons behind Thanc0/AC in 1E/2E

[GreyWizard77]

A friend of mine is playing through the Planescape PC game and is wondering why adding armor LOWERS AC, and a LOWER Thac0 is better. He's just recently started playing 3.5, so for him the current version of AC/BAB makes much more sense. Personally, I agree with him. I never really understood why the older editions had negative AC's.

I'm sure Gary had his reasons for originally designing things they were, but does anyone know some of the reasons behind the old design descisions?

 

[Ourph]

The simple answer is that the original concept for Armor Class was derived from another game that used a similar method. My understanding is that the term "Armor Class" refers to classifications in terms of "First Class Armor", "Second Class Armor", "Third Class Armor" etc. So, obviously, "First Class" armor (i.e AC=1) is going to be better than "Second Class" armor (i.e. AC=2) and so on.

 

[thedungeondelver]

The simple answer is that the original concept for Armor Class was derived from another game that used a similar method. My understanding is that the term "Armor Class" refers to classifications in terms of "First Class Armor", "Second Class Armor", "Third Class Armor" etc. So, obviously, "First Class" armor (i.e AC=1) is going to be better than "Second Class" armor (i.e. AC=2) and so on.

That is correct. It came from a naval battles wargame involving ironclads whereby "Grade 1" or "class 1" armor was better steel or iron than "class 2". "First class" versus "Second class" versus "Third class" all the way up to "Tenth class" (or ninth class, as the case may be).

 

[(Psi)SeveredHead]

A friend of mine is playing through the Planescape PC game and is wondering why adding armor LOWERS AC, and a LOWER Thac0 is better. He's just recently started playing 3.5, so for him the current version of AC/BAB makes much more sense. Personally, I agree with him. I never really understood why the older editions had negative AC's.

I'm sure Gary had his reasons for originally designing things they were, but does anyone know some of the reasons behind the old design descisions?

I'm glad you're getting reasonable responses to the question. I've seen this question asked many times, and often the answer is an elitist "to keep out the mental riffraff, of course!"

 

[Philotomy Jurament]

It's also worth pointing out that the older approach to AC wasn't as closely tied to the concept of a mathematical formula as it became, later. AC started out as an indicator of the type of armor you wore. In OD&D, very little modified your AC (not Dex, not magic armor, not magic rings, etc), and if your AC was 2, that almost always meant you were wearing plate mail and carrying a shield. Also, since the rules assumed the use of the combat tables, AC could just as easily have been designated with letters, instead of numbers. You weren't computing anything, you were just looking up the values on the appropriate table. This assumption is clearly seen in the 1E combat tables, with its repeating 20s that throw off any nice and simple formula. The old way of doing AC isn't math, it's a table heading.

In 1E, THAC0 was a formula that would work in many (but not all) cases (again, tables were the default assumption), was only referenced in the DMG's monster tables, and was never really explained. In 2E, THAC0 became the whole ball-of-wax. 2E abandoned tables, and made AC and "to hit" a formula you compute, instead. 3E is basically the same thing with the negative progression reversed to make the formula more intuitive.

One thing I've been toying with doing is house-ruling AD&D AC such that non-magical modifiers can never bring your AC below 0. This would create a symbolic break between "natural" and "supernatural" ACs (which almost exists in the RAW, anyway). I think I read about that idea on a Knights-n-Knaves or Dragonsfoot thread.

 

[RFisher]

I think for a number of game (board, war, role-playing, or whatever) designers--especially in that era--up/down, high/low were insignificant details. They really didn't think about it at all. & tables were generally thought to be more user friendly than formulas.

& as PJ pointed out, AC's direction was probably set before modifiers were applied to it, & THAC0 was derived from a table rather than being designed that way.

(In a Strategic Review article expanding the man-to-man weapon table for Chainmail, Gary used AC numbers, though they weren't used in Chainmail. Which suggests to me that PJ is right about the numbers originally being just an abbreviation rather than a mathematical quantity. Like "Mark I", "Mark II" or "first class", "second class", &c.)

 

[Cadriel]

I've always sort of liked the idea of Armor Class going down - it creates the idea of "AC 0" as a gold standard that just isn't there in 3.x. THAC0 was a much welcome simplification, but the problem in 2nd edition (the bulk of my experience) IME was that all the resulting subtraction was counter-intuitive, and one or two people at the table would wind up doing all of the AC calculations. When we switched to a system from Dragon that called it Attack Combat Value and Defense Combat Value (ACV / DCV) and made the numbers positive, it was pretty well received across the board. But even running Castles & Crusades these days, it's just plain weird to me to see AC 15 instead of AC 5. It was just the way it was.

- Wayne

 

[JDJblatherings]

AC stared out as an index and wasn't actually a score. It coudl have been A,B,C... also, it didn't matter as long as one could tell better from worse. Of course factoring in modifiers directly into AC screwed all that up.

Lets say your base aC was 5 and you had a 2 point bonus. I think it should have been written as AC: 5+2 meaning strike vs AC 5 and add 2 to the required score to hit. It even turned up that way now and again in old old olden days in some thrid party stuff.


Thaco as others discussed was initially a quickie short cut and similar methods turned up in the odl days as well. the monster&treasure asortments listed ones ability to hit AC 9 for a while and I've seen third party supplements listing NPc ability to hit AC 2. THACO is mathimatically easy and clean, except for it not completely working in 1st AD&D becasue there were repeated to hit score of 20 and over 20 here and there in the charts.

 

[Philotomy Jurament]

THAC0 was a much welcome simplification...

I've heard that a lot, so it must be a commonly-held opinion, but I don't see it that way. Typically, players had their "row" from the to hit charts written on their sheets; obtaining the number they need to hit doesn't get much simpler than glancing at the character sheet. No calculations required. THAC0 isn't a complicated calculation, but I don't see it as a leap forward in reducing complexity.

 

[Cadriel]

I've heard that a lot, so it must be a commonly-held opinion, but I don't see it that way. Typically, players had their "row" from the to hit charts written on their sheets; obtaining the number they need to hit doesn't get much simpler than glancing at the character sheet. No calculations required. THAC0 isn't a complicated calculation, but I don't see it as a leap forward in reducing complexity.

Well, I came into AD&D when 2nd edition was the rule of the day, so it's a bit different context, but in a lot of time online and a lot of play at the table, I can't remember anyone looking back with fondness on the old to-hit tables. (And I did actually talk a good deal to people who were into 1st edition -- I had all of the rule books from 1st ed. and used them pretty much interchangeably with 2nd ed. material.)

THAC0 and the 3.x BAB are the same thing expressed in different ways, and IIRC most or all of the charts were straightforward about the matter. The reason THAC0 was really welcome was simple: monster and NPC stat blocks could include a to-hit number and no further reference was needed.