OD&D Why is AC 2 the best armor class?

[Nikosandros]

From my understanding (which could be wrong), armor class derived from some naval wargame and is descending because, in OD&D, it is a "static" value which depends only on armor and shield and, thus, it is an indicator in which lower numbers represent a better "class" of armor. This makes sense. With only leather, chain and plate there is no overlap. Why then is the lowest class 2 and not 1? It seems to be that no monsters has an AC lower than 2, so it does not appear to be reserved for natural armor better than plate.

 

[Spectral Anomaly]

Monsters weren't worthy of having first class armor.

 

[Jack Daniel]

▯

 

[Nikosandros]

I don't know, but if I had to take a guess, it derives from baseline odds of 2 in 6. Lots of things in Chainmail and OD&D happen on 1–2 on 1d6.

If you average together all the saving throw numbers for 1st level characters of all classes, you get 14+ on the d20. That's 35%, pretty darned close to one third.

And the chance of a 1st level player character (THAC0 19) with no exceptional stats or magic to hit the median armor class, chainmail without a shield, AC 5? That also happens on 14+, or about a third of the time.

Since the to-hit tables are equally arbitrary, they could have shifted the tables and the ACs by 1 and obtained the same odds.

 

[Willie the Duck]

From my understanding (which could be wrong), armor class derived from some naval wargame and is descending because, in OD&D, it is a "static" value which depends only on armor and shield and, thus, it is an indicator in which lower numbers represent a better "class" of armor. This makes sense. With only leather, chain and plate there is no overlap. Why then is the lowest class 2 and not 1? It seems to be that no monsters has an AC lower than 2, so it does not appear to be reserved for natural armor better than plate.

Looking at the Chainmail rules, the instance where 'class of armor' is referenced (Individual Fires With Missiles) lists classes of armor as 1-8 (unarmored, leather, chain, and plate; each with- and without- shields). Shifting that right one nets you the 2-9 we see in oD&D. I don't see anything in Chainmail that exactly matches that. However, I'll note that the chance to hit (kill for singular unexceptional unit) chart Man-to-Man Melee table uses a 2d6 resolution system, with target numbers of 5+ (e.g. mounted lance vs. unarmored) to 12+ (spear vs. plate). If we flip that that to TN or less on 2d6, the same likelihood range is 9- to 2-. Thus it's always been my guess that the 2-9 range was for a planned 2d6 resolution matrix that was superseded by what we ended up getting.

 

[Nikosandros]

Looking at the Chainmail rules, the instance where 'class of armor' is referenced (Individual Fires With Missiles) lists classes of armor as 1-8 (unarmored, leather, chain, and plate; each with- and without- shields). Shifting that right one nets you the 2-9 we see in oD&D. I don't see anything in Chainmail that exactly matches that. However, I'll note that the chance to hit (kill for singular unexceptional unit) chart Man-to-Man Melee table uses a 2d6 resolution system, with target numbers of 5+ (e.g. mounted lance vs. unarmored) to 12+ (spear vs. plate). If we flip that that to TN or less on 2d6, the same likelihood range is 9- to 2-. Thus it's always been my guess that the 2-9 range was for a planned 2d6 resolution matrix that was superseded by what we ended up getting.

That's an interesting hypothesis.

 

[Gus L]

"I adopted the rules I'd done earlier for a Civil War game called Ironclads that had hit points and armor class. It meant that players had a chance to live longer and do more. They didn't care that they had hit points to keep track of because they were just keeping track of little detailed records for their character and not trying to do it for an entire army. They didn't care if they could kill a monster in one blow, but they didn't want the monster to kill them in one blow."

- Dave Arneson, UK Gamespy Interview (2004)

Not much to be had there. As far as why 2 is max AC instead of 1 I suspect it has something to do with the use of 2D6 as a determination dice in Chainmail .., but AC isn't meant to work with Chainmail so that doesn't really make sense. It's more likely an artifact of the "Ironclads" game - which I've never seen the rules for. Perhaps that used 2D6 as well and require a 2 to bust through the toughest armor? Wild conjecture really.

I do like a game where the max AC is 2 descending/18 ascending because it makes armor beside plate and shield more viable for PCs and makes it so at higher levels everyone almost always hits. This in turn favors more interesting special abilities and magic item abilities in my experience. Otherwise the combat game becomes a race to -5 AC or lower by mid levels.

 

[Moving Pictures]

I do like a game where the max AC is 2 descending/18 ascending because it makes armor beside plate and shield more viable for PCs and makes it so at higher levels everyone almost always hits. This in turn favors more interesting special abilities and magic item abilities in my experience. Otherwise the combat game becomes a race to -5 AC or lower by mid levels.

When I rebooted, I had no armour at zero. Boiled leather at 3. Mail at 5. Shields adds 2. Easy to do the combat stuff as well.

 

[Bill Zebub]

Somewhere in here is a really clever Spinal Tap reference.

 

[James Gasik]

2e Red Dragons: "our AC goes to -11!"