Or . . . Why the Alternate Combat System became the StandardI've been meditating on the Weapon Vs. AC system I proposed and used a while back. As much as I like the idea intellectually, it has done much to make me realize why the "alternate combat system" of 0e became the default in later editions. When using a static "to hit" chart and an increasing number of attacks per round per round as in the Chainmail rules, the result is a combat system that is quick and brutal. Hit points do not outstrip the ability to do damage as in the alternate combat system. A 4HD creature has the capability to kill 4HD worth of opponents per round. Initiative becomes exponentially more important than in the alternate system and finding a way for combat to be anything other than a brief and brutal bloodbath is difficult.
For example, imagine a party of 4th level characters. To make things simple, I'll say they are all fighters. This means that the party has the capability to kill 16HD worth of monsters per round. If we assume that fighters are all armed with swords and they are going up against orcs wearing chainmail, this means the fighters have a 30% chance to hit per attack, using the table I used when I playtested my own version of the Chainmail rules using a d20 system. Using d6 damage and assuming the fighters have a +1 to damage, this means on average the fighters will do 22 points of damage per round (16 attacks x .3 chance to hit x 3.5+1 average damage). Compare that to the alternate system (as per LL) the same group of fighters would only do an average of 7 points per round (4 attacks x .4 chance to hit x 3.5+1 average damage). In other words, between four and five orcs are going to die every round versus one or two with the alternate combat system.
In order to make combat last more than one or two rounds and thus have any kind of meaning or drama, the number of HD brought to bear needs to be of a value close to that of the fighters; however the closer the HD equal each other the more likely it is that the fighters will have a casualty, especially if they lose initiative. In the end, I don't know how fun this system would be, especially when compared to the excitement the alternative combat system can generate, especially at higher levels.
Thus, it is no surprise that the alternate combat system quickly became the default combat system.
Thus, I have come to the conclusion that the direction I have been taking on Weapon vs. AC is as practical as the tables found in the 1st ed PHB (meaning not practical at all). This has me trying to think outside the box. Which brings me to the concept of a dynamic AC system. This could get complicated and ugly quickly, so I've been thinking of a simple, abstract system that includes the normal Base AC that we are all familiar with. Then there would be two other Armor Classes, indicating armor vs. a weapon class. These would be a simple +/- 1 and could be abbreviated sAC (slashing), bAC (blunt) and pAC for piercing. For example
Leather: AC = 7; sAC = 8; bAC = 6
Chain: AC = 5; pAC = 6; sAC = 4
Plate: AC = 3; bAC = 4; pAC = 2
Otherwise, combat proceeds as normal.