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

[GreyLord]

Some thoughts...

Because, as it was derived...a 1 is an automatic miss.

I know...I know...that's not how it works in D&D with the AC vs To Hit Tables...but...

Yes...a 1 is always a miss.

Other reasons...it's guessed at strongly above, but it wasn't due to Chainmail, I don't think (Personal opinion) but the naval rules it was based off of. Also, using a 2d6 means that 2 was the lowest roll.

If your ship was an AC 12, (I know...I know...it only goes up to 9 or 10 depending on the version of D&D), it was automatically hit every time you attacked. No ship was that bad.

A 10 would mean that if you rolled a 10 or lower, you hit. A 9, 9 or lower you hit...and so on and so forth.

If you had an AC of 1, no one would ever be able to hit you (invulnerable ship). An AC of 2 meant that you would have to roll snake eyes to hit this thing...and that was pretty hard to do as well.

That is, until you start using a D12 or D20.

 

[Willie the Duck]

Assuming it is 2-9 to work with a 2D6 system: Without knowing the naval game in question it's conjecture whether the actual system was 2d6, if it's porting a Chainmail mechanic, or it was made up on the fly. Unfortunately, all searches I do for naval games or wargames called Ironclads reference modern games on Steam or a game first published in 1979.

Anyone have Jon Peterson's work at hand? I bet he's gone into inspiration for Hit Points. If Dave thinks the same game gave him the idea of HP and AC, Jon may well have reference to the actual game that would include published or some other search terms (or maybe even an overview or some visuals).

 

[Mannahnin]

Assuming it is 2-9 to work with a 2D6 system: Without knowing the naval game in question it's conjecture whether the actual system was 2d6, if it's porting a Chainmail mechanic, or it was made up on the fly. Unfortunately, all searches I do for naval games or wargames called Ironclads reference modern games on Steam or a game first published in 1979.

Anyone have Jon Peterson's work at hand? I bet he's gone into inspiration for Hit Points. If Dave thinks the same game gave him the idea of HP and AC, Jon may well have reference to the actual game that would include published or some other search terms (or maybe even an overview or some visuals).

My recollection from PatW is that Fletcher Pratt's naval wargame (started 1937, first published 1940?) was one of the earliest sources for the concept of units accumulating points of damage. I've attached an image of a ship damage chart from this game. The numbers on the left indicate the damage thresholds at which effects degrading its performance (speed and weapons) accrue, and on the right the exact effects. So it takes 743 points of damage before it starts to slow, and 23,034 to sink it.

Wait, no one's linked the 2018 article from Jon's blog yet?

Why Did Armor Class Descend from 9 to 2?

One of the great riddles that has vexed D&D players for generations is this: why did armor class in original D&D descend from 9 to 2 inst...

playingattheworld.blogspot.com

 

[Nikosandros]

My recollection from PatW is that Fletcher Pratt's naval wargame (started 1937, first published 1940?) was one of the earliest sources for the concept of units accumulating points of damage. I've attached an image of a ship damage chart from this game. The numbers on the left indicate the damage thresholds at which effects degrading its performance (speed and weapons) accrue, and on the right the exact effects. So it takes 743 points of damage before it starts to slow, and 23,034 to sink it.

Wait, no one's linked the 2018 article from Jon's blog yet?

Why Did Armor Class Descend from 9 to 2?

One of the great riddles that has vexed D&D players for generations is this: why did armor class in original D&D descend from 9 to 2 inst...

playingattheworld.blogspot.com

Thanks for sharing this, I was sure that something like this article was out there.

Still, it is all very arbitrary. I almost prefer (from an esthetic point of view) the 2d6 roll under explanation. The system described in the article could work equally well with AC starting at 1 and going up to 8: you just add the AC to 10 to get the required to-hit number.

 

[Willie the Duck]

Wait, no one's linked the 2018 article from Jon's blog yet?

Why Did Armor Class Descend from 9 to 2?

One of the great riddles that has vexed D&D players for generations is this: why did armor class in original D&D descend from 9 to 2 inst...

playingattheworld.blogspot.com

Is why I asked. For some reason my work internet blocks his blog, so he's often unavailable when I'm thinking of these discussions. Pulling up now on my phone.

Hmm. I don't actually like Peterson's logic -- AC is the number you subtract from 20 to get the number-or-higher a first level fighter needs to roll on a D20 to hit in the initial-draft oD&D. That explains what mathematically it is, but not why it is labelled 2-9 -- in that framing, it could have just as easily been 11-18 (or 0-7, as the number you subtract from 18 to achieve the same results, etc.) -- nor is it evidence that that is the why of the labelling. We're still missing a part of the causal chain, or at least Gary saying something like 'yes, it's just what I subtracted from 20 to get the hit percent I wanted.'

And it looks like, unsurprisingly, Gary and Dave disagree on the inspiration for AC. At least in this case it is reasonable, as how it differs from any wargame with different to-hurt numbers by troop type is a matter of degree, not type. So if Dave maybe thought he was borrowing from elsewhere for his proto-D&D and Gary thought it came straight from Chainmail, quite possible that that didn't bridge the communication between them as they collaborated on the game. Good to know that Peterson too can't definitively find the specific game Arneson was using.

My recollection from PatW is that Fletcher Pratt's naval wargame (started 1937, first published 1940?) was one of the earliest sources for the concept of units accumulating points of damage. I've attached an image of a ship damage chart from this game. The numbers on the left indicate the damage thresholds at which effects degrading its performance (speed and weapons) accrue, and on the right the exact effects. So it takes 743 points of damage before it starts to slow, and 23,034 to sink it.

A reasonable candidate, although honestly it might be a little old (do you know if there were reprints?) and some subsequent game that took that concept from it would be more likely. Especially when we consider games he himself might not have owned, but had access to from his wargaming friends, it's really hard to ge a complete picture of what he might have had access to (we can rule things in, but ruling them out is a real beast).

What interests me most about this game (other than those strangely high hp totals, like was there a value to that granularity?) is that it has degradation of combat effectiveness as you lost hp. D&D rather famously doesn't have that (cue discussion about monster at 1 hp still getting full counterattack). Now, it could be that Dave simply didn't port that part over, since the piece he wanted was simply a state in between full health and dead (to ameliorate the player frustration previously discussed). It could also mean that the game he borrowed it from (if I'm right about it being a subsequent game which stood on Pratt's shoulders) didn't have this.

 

[Moving Pictures]

Hmm. I don't actually like Peterson's logic -- AC is the number you subtract from 20 to get the number-or-higher a first level fighter needs to roll on a D20 to hit in the initial-draft oD&D. That explains what mathematically it is, but not why ...

I have AC starting at zero and ascending logically. Math works with a 2d10 to hit, Roll must >=10-F+AC.
So the math explains diddly.

Descending AC never made a lick of sense.