|Semi-relevant image from Wikipedia
Prior to second edition D&D, the attack progression of characters is jumpy. In OD&D, for example, fighters don’t improve at hitting things until 4th level, and progression is even slower for other classes. This system, in the original conception (where all classes use the same chart, but get better at different rates) can be thought of as attack ranks.
Rather than an attack bonus, DCC RPG has fighters use an attack die (plus a small additional bonus at high levels). In effect, fighters determine the attack bonus randomly round by round. This only applies to fighters and dwarves though; all other classes use standard d20-style fixed attack bonuses. The results of the die used to determine attack bonus (called the “deed” die) also feed back into the DCC stunt system: a deed result of 3 or more results in a successful stunt.
Recently, I also thought about promoting attack ranks to first order game constructs that could be used in ways other than just attack bonuses. Specifically, attack ranks could be used defensively. This would allowing fighters to “spend” attack ranks on a round by round basis to improve their own AC or defend companions. This idea can be expanded to cover other areas of combat.
Rather than using a better attack matrix (or improved attack bonus), characters have a number of combat dice equal to the combat rank. In my adjusted attack rank system for OD&D, fighters start off at attack rank 2 and top out at attack rank 6 (at high level), while clerics (for example) start at 1 and top out at 4. Using those numbers, fighters would start out with 2 combat dice, which could be used for various things.
I see four main ways to use combat dice: attack bonus, personal AC bonus, defending companions, and extra damage (though not all classes would have access to all options). Basically, this allows players to change focus between offense and defense round by round, but since the number of dice is relatively small (between 1 and 6, inclusive) there are fewer choices to consider (and thus reasoning will probably be more diegetic and less about mathematical optimization).
Combat dice options by class:
- Fighter: attack, armor, defend, damage
- Cleric: attack, defend, armor
- Thief: attack, damage
- Magic-user: none
Thus, combat dice become general resources that all classes use and they replace the other attack progression system. In some sense, the tenor of combat for a specific class becomes the combination of how fast combat dice are acquired and what they can be used for.