The module A3 Assault on the Aerie of the Slave Lords has an interesting appendix - rules for loosing missiles into melee.
The DUNGEON MASTERS GUIDE also has some on p. 63. Let's compare.
It starts off with one of those really pedantically overstated Gary Gygax lines, before it gets into a long and complex discussion of the issue that is naturally described as "easily handled."
"Likewise, discharge of missiles into on existing melee is easily handled. It is permissible, of course, and the results might not be too incompatible with the desires of the discharging party. Assign probabilities to each participant in the melee or target group according to sheer numbers. In the case of participants of varying size use half value for size "S', normal value for size "M", and one and one-half value for size "L" creatures which ore not too much larger than man-size. Total the values for each group and ratio one over the other. If side A has 4 man-sized participants, and side B hos 3 smaller than man-sized participants and 1 size "L" bugbear, the ratio is 4:3. Then, according to the direction of the missile discharge, determine hits by using the same ratio. If 7 missiles were loosed, 4 would have o chance to hit side A, 3 side B. In cases where the ratio does not match the number of missiles, convert it to a percentage chance: 117 = 14% or 15%, depending on whether the missiles are coming from ahead of side A (14%) or from behind (15%). Thus 4/7 = 56% or 60% chance per missile that it will hit side A. The minor difference represents the fact that there will be considerable shifting and maneuvering during combat which will tend to expose both opponents to fire on o near equal basis. Such missiles must then be assigned (by situation or by random determination) to target creatures, a "to hit" determination made, and damage assessed for those which do hit."
It's probably explained in a more complex manner than it needs to be, but even so, the steps are:
- determine how many combatants and their size to establish a ratio
- use that ratio to split up missiles
- determine a target
- roll to hit.
It does state later that for sufficiently large targets you can just toss this - "this writer, for instance, always allows archery hits to hit a giant or a similar creature engaged against a human or similar opponent."
A3 has a different version* on p. 23:
"Tournament Missile Fire into Melee
If characters wish to fire missiles into melee, the following simpler system shall be used in place of normal AD&D procedures (described in the DUNGEON MASTERS GUIDE):
1. A specific target is declared by the player.
2. The DM secretly determines the real target, as follows:
a. Find the total "man-sized units" present in the melee pairing (as opposed to the entire melee); small creature = 1/2, man-sized = 1, larger = 1 1/2, huge (e.g. anhkheg, dragon) = 2.
b. Roll randomly to determine which man-sized unit becomes the target of the missile: determine by half-units if necessary.
3. The player rolls a "To hit" roll, announcing the adjusted total to the DM.
4. The DM compares the number to the armor class of the actual target (not necessarily the intended one) to determine hits.
5. ANY miss will miss the entire melee, and NEVER hits an alternate target.
EXAMPLE: Blodgett (halfling thief, AC 3, rear AC 7) tries to slip around behind a melee with gnolls,but is spotted and attacked by 2 of them. Freda the Forester decides to help with arrow fire. The total number of man-sized units is 3 1/2 (1 1/2 per gnoll, 1/2 for the halfling). The DM rolls a d8: 1-3 = 1st gnoll, 4-6 = 2nd gnoll, 7 = Blodgett, 8 = reroll. Unfortunately,a 7 is rolled, and Freda's "To hit" roll is compared to Blodgett's REAR AC (7)to determine the results of the shot.
In these cases, a character target's AC must be carefully determined: rear AC isthe most commonly encountered, but occasionally only shieldless AC is used. If a character expects missile fire, include dexterity adjustments to AC."
That does seem significantly simpler than the DMG version. It's easier to do it missile by missile instead of a system that works better if you determine all of the missiles fired and then start to divvy them up.
What's odd to me is that in either case:
- there is no chance to hit the wrong target if you miss the selected target, something I've gotten very used to in GURPS. A miss, misses everyone.
- and moreover, your skill doesn't help you hit the target you want to. Even if you're a DEX 18 10th level fighter with a Crossbow of Accuracy +2 and a Bolt +2, you can't easily pick out an unfriendly target. You take your chances and then see what happens. The better your "to hit" the more dangerous it is for you to fire into a melee with a friendly. You almost may as well if your allies have great AC and you have a sucky "to hit" roll. If they have lousy AC or you are very accurate or both, they are more at risk.
I think the next time we play AD&D we'll use the A3 system unless I come up with one I like on my own. It seems like you should just have a penalty to hit a specific target, and a chance to hit the wrong target. That could just be my experience with GURPS talking, but that does both reward high skill with a better ability to sort friend from foe in a melee and punish failure by seeing if someone else took the hit. Is there a third system floating out there that does this?
* I'm not sure why this is in A3, in any case. It's not like there is any more or less combats that could involve missiles fired into a melee. Maybe this was the first time there was space to fit it in.