Thoughts on Man-to-Man in D&D

Dragons fight as "4 heavy horse", which is simple on the mass Combat table, but unclear on Man to Man.
But wait, "Barding" is an armor option on the M2M table.
Dragon armor rating can simply be equal to Barding, with the appropriate number of Hit Die as referenced in D&D Book 2.
Then they also have that Achilles Heel of being shot out of the sky by a Hero on a roll of 12

I'm not a fan of multiple attack rolls. One "chance to hit" per attack is enough.
Hit Points should (and do) replace simultaneous hits with cumulative hits. There's no need to model extra attacks or anything on top of that.

Light, Heavy and Armored Foot troop types can map directly onto the Leather, Chain, and Plate armor types.
Light,  Medium, Heavy and Draft Horses are purchasable mounts in D&D, and with the addition of Barding can be armored.

In Chainmail, while flanking, the defender is hit as if he was one lower troop type. This correlates to a 2 step drop in armor type on M2M, with consideration given for a shield. It's also probably the origin of the "+2 to hit" rule in AD&D. In both AD&D and Supplement 1, the right flank gets no protection from a shield.

Digging into the Chainmail M2M rules has given me a new appreciation of Supplement I: Greyhawk as merely an attempt to translate Chainmail rules into the D&D chassis. The implementation is a bit tortured and some of the math is wrong, but its what we've come to expect from Gygax. I feel like a fuller explanation of the imported systems would have benefited the supplement, and apparently Gygax did too, as that's what he wrote in AD&D (and had issues describing it there as well)

House rules for D&D + Chainmail

The races: Human, Elf, Dwarf and Hobbit

The classes: Fighting-Man, Magic-User, Cleric

No multi classing, elves must choose a single class

Stats are rolled 3d6 arrange as desired, starting gold is 3d6x10 for personal equipment 

There are no hit points. A single hit is death for Man- type characters. It takes 4 concurrent successes on d6 for a Man to hit a Hero.

In almost all cases the Mass Combat Table will be used for combat resolution, the Man-to-Man Melee table will only be used for individual combat between Hero types and those rare cases when it applies against Monsters

Super Heroes may roll twice on the Man-to-Man Melee table to attempt to hit a Hero. Hero and Super Hero will use the Mass Combat table against Man characters.

The Man-to-Man Combat Table and D&D

I don't think the Man-to-Man table was ever intended to be used with D&D. The Mass Combat rules dovetail so nicely with both the Fighting Capability column and Monster HD that it does feel like the game was developed out of those rules, while the M2M table and D&D's level progression seem at odds with each other. Generally, every attempt to reconcile them has some struggles - the very first can be seen by Gygax himself in Supplement 1: Greyhawk.

I've seen some implementations that try to use the M2M table as the universal melee resolution mechanic for D&D, but I think that only works when two combatants are of the same type. For example, if two men are fighting or two heroes. In the case of Man vs. Hero or Superhero, it makes more sense to me to revert to the Mass Combat rules. I prefer squad combat and simultaneous hits over individual combat and tracking hitpoints over multiple rounds. Actually I don't even use hitpoints in the PbP game that I'm running, just the appropriate number of successes on d6 for a hit.

If you select the M2M table for use only against opponents of the same category, then you can still involve the "Fighting Capability" column of D&D for bonuses. For example, a "Man + 1" would roll 2d6+1 for his chance to hit another Man

OD&D + Chainmail

 I love this so much. It really makes OD&D so much more playable when you just use it as a campaign system for Chainmail. So while all battles would be fought with Chainmail, OD&D would be used to calculate overland campaign movement rates, fleeing success, terrain types, random encounters, treasure, and allow a method whereby your troops get stronger and become hero types.

I've seen a lot of attempts to meld the d20 combat system with Chainmail's Man-to-Man combat table. The two earliest attempts were from Gary Gygax himself, first in Supplement 1: Greyhawk and again in AD&D 1e. I like the 1e table and I use it when I play AD&D, but for OD&D I think it's better to ditch the d20 system completely and only use Chainmail's d6 dice pools and 2d6 system.

I only use the Man-to-Man table in the case of Hero vs Hero combat or in the rare instances where it applies to Hero vs Monster combat. For everything else I use the Mass Combat system detailed earlier in Chainmail, where it takes a minimum of 4 light footmen to damage 1 heavy horseman. That means that if the player only has 3 light footmen, the heavy horseman is functionally invincible against them and can damage them with impunity. This is the expected result when strong monsters, such as dragons, attack regular troops.

This system works best with large troop numbers, so it isn't well suited to underground dungeon crawls with a small group of characters. Which is fine, as it works really well for overland campaigning with large armies and mass combat. Raising and maintaining an army is a huge money sink in this game and justifies a constant need for treasure. In fact I find it interesting if the players immediately jump into overland campaigning on day 2 of their adventure, after having gotten just enough gold to raise their first contingent of soldiers.