1) Determine surprise
This isn't as difficult as it sounds, even though it takes about five readings to understand. Roll a d6 for each side, 1 or 2 means that side is surprised. There is a chart on pg. 62 that can be extrapolated to cover just about any surprise conditions. Each segment of surprise allows a full round of combat actions for the unsurprised party. However, DEX adjusts this and does not allow melee nor missile attacks (from what I can determine) to affect certain individuals. A thief with a 17 DEX (+2 reaction) would only be a viable target if there were 3 segments of surprise. All those spell casting times rated in segments make more sense now: Magic Missile and Sleep can be cast during 1 segment of surprise. Supposing there were 2 segments of surprise and a MU cast Fireball; the spell would occur on segment 1 of the first combat round, regardless of initiative. Considering some of the rules about interrupting spell casting during melee, it's not a bad idea to start casting a lengthy spell during surprise. This does mean that high level wizards who surprise parties can royally fuck them up beyond belief. This is counteracted by being pathetic during regular melee, and pretty much a liability when facing high level fighters unless they have some sort of magic item. I knew there was a reason for all those staves and wands...
2) Determine distance
Again on pg. 62 there is extensive detail on how to determine distance. Unless charging, it takes 1 segment to move 1" (10'), so melee is generally impossible unless surprise occurs within 10' initially. Moving during surprise segments is a valid action, so if 2" separate the combatants, using 2 segments of surprise to close the gap is a good idea. In retrospect, I always thought surprise was ridiculously overpowered, but really, using the distance rules it's really not that bad. Essentially you catch a monster with its pants down 30' away, you run up to it before it has a chance to figure out what's going on. If it bumbles around a corner, smack the hell out of it before it can react, etc. Anyway, this is vitally important because if the distance is far enough, the first melee round will be combatants moving into position, giving spell casters an opportunity to do some damage. If it's close, the wizard better pull out a wand or staff.
3) Determine initiative
There is a document called ADDICT which essentially does the same thing this post tries to do, but much more complexly. I believe it comes to the same conclusions, but goddamn the section on initiative is hard to comprehend. Basically, a d6 is rolled per side. Higher roll goes first, ties result in simultaneous actions. High level fighters with multiple attacks go before everyone else, no matter what the initiative says, their attacks staggered as necessary. If firing a missile, the reaction bonus is added to personal initiative roll. This last part resulted in an epiphany: DEX doesn't help bows hit. It helps them fire sooner during a round. Given later information in the DMG about bows created to utilize STR bonus, it makes perfect sense. STR is the only ability that helps attacks hit. Period. Anyone complaining about fighters not being very good needs to use all the rules...
4) Determine actions
This is actually detailed fairly well; specific actions occur before others.
- Run away
- Fire missiles, use magic devices, cast spells, turn undead
- Move or charge
- Set weapons against charge
Now comes all the fun stuff...specifically spell casting during melee. Page 65. Reading through this section, you are an idiot if you cast a spell during a general melee unless you have some beefy fighters for protection. No movement, no DEX bonus to AC, can be interrupted with a successful attack. If on the losing side of initiative, an attack will always occur before the spell goes off. This also means high level fighters get to attack before any spell can be started. Ouch. Tied initiative, compare weapon speed to casting time in segments. I KNEW WEAPON SPEED WAS THERE FOR A REASON! If initiative is won, the initiative rolls subtracted from weapon speed to determine segment of attack and compared to casting time. This means if a MU won initiative and is casting Sleep (1 segment), he can be interrupted by a punch, but that's about it. Daggers can disrupt a Fireball, however, even if initiative is lost. During tied initiative, weapon speed is further used to see which side attacks first. This only occurs when weapons are used; against natural (monster) attacks, simultaneous attacks mean both take effect. Further, multiple attacks are possible if the weapon speed is more than twice as much (or 5 total), 1 additional attack is possible. 10 or greater, 2 attacks before and 1 simultaneous attack. Certainly a reason to use a dagger in melee, right?
More fun stuff: picking a specific target in melee is generally not possible. The DMG recommends randomly determining targets. Breaking away from melee results in a free attack with no DEX bonus, shield bonus and at +4. Vicious. Getting really drunk is beneficial for villagers against high-powered opponents. They get a +3 to hit points which easily outweighs their -5 to attack; if you have to roll a 20 to hit, what's the difference? Speaking of 20s, the to-hit chart implies a natural 20 is required to hit certain ACs, and a natural 20 with bonus required to strike extremely low ACs. Further, a 1 isn't an automatic miss. In fact, high level fighters with magic items and great strength pretty much hit everything, every time. For example, a 17th level fighter with an 18/00 STR and a +5 weapon will hit AC -5 or below without even rolling. Any roll of 6 or higher will hit AC -10, or literally 75% of the time. High level paladins fucking up demons beyond belief is very plausible...
After going through this, I decided to re-read ADDICT in detail. To be perfectly honest, it IS exactly how AD&D combat is performed, but holy shit, good luck doing it that way. Strangely, there aren't any contradictory rules if you take the system as a total as opposed to piecemeal. I don't think I'm ever going to run combat this way, but it gives me a good reason to consider weapon speed factors. Quite frankly, I always hate the way spell casters dominate melee, casting spells that determine the outcome of every fight. Using the AD&D combat system, they'll rely greatly on magic items and use spells rarely during fights and instead focus on more utility magic. That's pretty awesome.