A monster on the verge of eating an adventurer.

Ascending AC for OD&D

by Ramanan Sivaranjan on December 23, 2014

Tagged: mastersofcarcosa od&d

I have been using ascending AC for my OD&D Carcosa game. Players roll a d20 to hit, add their attack bonus, and try and score higher than their opponent’s AC. An unarmoured combatant has an ascending AC of 10; plate armour and a shield confers an AC of 17. It’s a much simpler system for adjudicating combat in my opinion. People know if they have hit or not without having to look at a table, and the arithmetic is all quite straight forward.

What follows are the tables from the first OD&D book MEN & MAGIC redone so they work with ascending AC. (I am certain I am not the first person to do this, but there wasn’t an obvious hit when I looked on Google.)

The attack bonus progression for the Fighters is:

Level Attack Bonus
1–3 +0
4–6 +2
7–9 +5
10–12 +7
13–15 +9
16+ +12

For Clerics:

Level Attack Bonus
1–4 +0
5–8 +2
9–12 +5
13–16 +7
17+ +9

And for Magic-Users:

Level Attack Bonus
1–5 +0
6–10 +2
11–15 +5
16+ +7

Monsters use the following table.

HD Attack Bonus
up to 1 +0
up to 2 +1
up to 3 +2
up to 4 +4
up to 6 +5
up to 8 +6
up to 10 +8
11+ +10

The tables are simple enough to make. In a descending AC system a first level characters needs to roll a 10 to hit AC 9 (an unarmoured person), which we determine by looking at the attack table in MEN & MAGIC. To hit that same character who has an ascending AC of 10 by rolling a 10 (or more) implies a 1st level character has no attack bonus. A 4th level fighter only needs an 8 to hit that same character, so their attack bonus is +2.