When I recently played in Evan’s Uz campaign, he had hit dice do double duty as attack bonus. Uz is based on Swords & Wizardry WhiteBox, which, like OD&D, only uses the d6 for hit dice (modulating the difference between classes using bonuses as described here). The elegance of this approach impressed me. Only one number is required for both hit points and offensive ability. And it generalizes to monsters, though you might want to cap the bonus depending on the campaign power curve (max +10 seems pretty reasonable to me).
I don’t remember exactly how he did it, but this is how I might do something similar. Fighters find their attack bonus by adding their hit dice expression together. For example, a fighter with HD 5+1 has a +6 attack bonus. All other classes ignore the bonus part of the hit dice expression and just use the base HD. So, a cleric with 4+1 hit dice attacks with +4. Tougher classes always have more hit dice than weaker classes, which is also how attack bonuses should work.
This is what the attack bonuses would look like given the recently posted rationalized hit dice progression (hit dice are in parentheses):
|1||+2 (1d6+1)||+1 (1d6)||+1 (1d6)|
|2||+3 (2d6+1)||+2 (2d6)||+1 (1d6+1)|
|3||+4 (3d6+1)||+2 (2d6+1)||+2 (2d6)|
|4||+5 (4d6+1)||+3 (3d6)||+2 (2d6+1)|
|5||+6 (5d6+1)||+4 (4d6)||+3 (3d6)|
|6||+7 (6d6+1)||+4 (4d6+1)||+3 (3d6+1)|
|7||+8 (7d6+1)||+5 (5d6)||+4 (4d6)|
|8||+9 (8d6+1)||+6 (6d6)||+4 (4d6+1)|
|9||+10 (9d6+1)||+6 (6d6+1)||+5 (5d6)|
|10||+11 (10d6+1)||+7 (7d6)||+5 (5d6+1)|
Another way to look at this rule would be that all classes use base hit dice as attack bonus, but fighters get an additional +1. Or, one could just use the additive hit dice for all classes, which makes things simpler (no special case for the fighter) at the cost of decreasing the relative power of the fighter slightly.
Using this system necessitates running with ascending AC. I have actually been considering switching to ascending AC off and on for a while now anyways. This attack bonus system is probably simpler and easier to understand than my attack ranks system, and it does away with another table (usually a good thing).
Instead of switching to AAC, use Philotomy’s system: take the characters attack bonus (which you described) + d20 + opponent’s AC (using regular THAC0 AC). If this is greater than 20, the character hit. This gives players a nice simple rule to remember and you get to keep the original AC.
That’s a good alternative, but it does mean that I have to reveal target ACs, which feels weird to me. That’s always been something that I have kept behind the screen, along with enemy hit dice and HP remaining.
I have been using HD as attack bonus in plenty of games with great success – and also with descending AC and the Target20 system described above.
I don’t understand why the Referee should reveal AC in this case, though; the player simply rolls, add his HD, and says the number – it’s up to the Referee to tell him if he’s hit or missed.
I suppose you are right. Player takes die number and adds hit dice, referee adds (descending) AC to that number and checks if it is higher than 20. Not intuitive for me, but that’s probably because I’m not used to target 20. After a few games, I bet it would become natural.
I’ve been using HD as fighter levels so I only have one to-hit table. A Magic-user with 4 hit dice is treated as a level 4 fighter (I’m not big on niche protection for Fighters don’t get special rules). I’m surprised that it wasn’t this way from the beginning. Perhaps, those early designers felt that attack chance and hit points shouldn’t be directly tied together. I noticed that in Dragon #1, Len Lakofka produced a variant set of rules that game monsters a separate attack level (called “Strength”) independent of their hit dice.
Hit dice as attack modifier is exactly how I use it in my shortened multi-edition stat blocks.