From what I understand, Dave Arneson replaced the Chainmail Combat System with a rule system using the Armor Class Mechanic which he based on concepts from a naval combat game called Civil War Ironclads.

It seems to me that this was a pretty brilliant move. I dont know much about Chainmail, but so many other RPGs involve an attack roll, followed by a defense roll. One of the advantages of AC is that you eliminate one of the dice rolls, speeding up combat considerably.

The odd side of AC in D&D is of course that it doesnt distinguish between attacks that miss the opponents and attacks that hit, but dont cause damage.

What do you think of the Armor Class rules?

-Havard

1. "Civil War Ironclads" was, as I remember it, a game also written by Dave but never published.

2. I think that the attack value versus defense value (which was also the main combat system behind most Avalon Hill and SPI wargames of the era) is much more efficient than what later RPGs put together in the name of "realism." Adding in parry or dodge or armor absorption rules simply slows the whole process down.

3. As to AC, I still have frustration that low is better and this is a rule I "fixed" decades ago in my own game. I can see where it comes from, however, when "First Line" or "First Class" ships were the best ones, "Second Line" were second best, and so on. Logical in context, perhaps, but illogical in a RPG, unless...

4. ...my personal theory is that one of the early combat systems goes back to 2d6 and trying to roll under AC to hit. This also explains why the best AC in the original game was 2 instead of 1. So, to hit an unarmored foe (AC9) you would have to roll 9-12 on 2d6, but to hit someone in plate and shield (AC2) you would have to roll 2 on 2d6. I would still have reversed it (let plate & shield be AC12 and unarmored be AC5, for example) so you would roll under, but that's just one guy's preference. :P