Double Trouble

Two weapon fighting, or dual wielding, is a common trope in modern fantasy - ingrained by future editions, but absent from the original Basic line; likewise missing from many a retro-clone. Commonly house-ruled, commonly back-ported, and commonly discussed - here are my rules for fighting with two weapons in a B/X-compatible game. This rule is designed for two-weapon fighters to provide versatility to the character at the cost of maximum effect: a parrying dagger will never be as effective as a kite shield; nor will a side sword empower you to strike as heavily as hefting a mighty zweihander.

Dual-Wielding, or Fighting with Two Weapons

When fighting with two weapons, a character may choose to fight in one of two positions: an offensive position (or, striking) or a defensive position (or, parrying).

• When striking, a character is presumed to be attacking with both weapons: using one to feint and then the other to strike; using one to trip or engage the shield while looking for an opportunity with the other; or perhaps even coming down with both in haymaker swings. A character so positioned gains a +1 bonus to hit on their attacks.
  
  
• When parrying, a character is presumed to be attacking with one weapon, but using the other to distract, to parry, or perhaps to ward off opponents, keeping distance between the two of them, such that they become more difficult to hit. A character so positioned gains a +1 bonus to their Armor Class against melee attacks only.
  

A character which is surprised should benefit from neither during the surprise round, adopting a position, or stance, in the first combat round in which they are aware of their adversaries.

Note, a "bonus" of +1 in any sense should benefit the character to whom the bonus is applied. Specifically, when using descending armor class, a +1 bonus to armor class will, numerically, reduce the armor class value by 1 point: making the beneficiary more difficult to hit.

Optionally, when fighting with two weapons of mismatched size - that is, say, a sword dealing d8 and a dagger dealing d4 - the referee may rule that, on a hit exactly matching the armor class of the target, damage is dealt using the off-hand weapon. So, for the character with the sword and dagger striking an adversary of AC 6, a successful hit on AC 5, 4, 3, or so on would deal 1-8 damage; whereas a successful hit on an AC of 6, explicitly, would instead deal 1-4 - potentially making an exception if striking an adversary against whom a natural 20 is required to hit.

Optionally, when a character in an offensive stance scores a critical hit - that is, rolls a natural 20 on the attack roll or otherwise performs in a manner determined by the referee to constitute a critical success - the referee may allow the player to roll the damage dice of both weapons, either summing the result or taking the better of the two, depending on the referee's situational jurisprudence.

Optionally, when a character in a defensive stance is hit in melee exactly on their AC, the referee may allow them to disarm themselves of or to damage or destroy their off-hand weapon in order to negate the hit. So, for a character with an AC of 5 that is parrying against an Ogre, if the Ogre rolls to hit AC 6, 7, or so on, the character is safe; however if the Ogre rolls to hit AC 5, the referee may allow the player to declare that the force of the blow sends their parrying arm into the stone floor, snapping it in half - but dealing no damage to the character. Were the Ogre to hit AC 4, 3, or so on, the parrying character would be hit normally.

Why have "stances" as opposed to static bonuses? The objective is to produce versatility, not to grant an advantage. It is intended to be no more powerful, nor less powerful, than sword-and-board versus great-axe approach. By forcing a decision between two options, slightly less powerful than similar options that do not allow for the decision to be made, it grants different advantages under different circumstances: which is neutral, in terms of benefit to drawback.To grant static bonuses would, in my opinion, make the ability objectively better.

Why a to-hit bonus? There should be consequences of wielding two weapons. If it's all fluff, that is - your character has no changes, mechanically, to the game when fighting with two weapons - then they have no incentive to do it over using a two handed weapon. This is fine for some referees who don't want dual-wielding in their games, citing style or historical reasoning - for them, I say (though the historical reasoning is flawed) ignore this suggested ruling. For me, though, I want to include it - and for other referees who enjoy a bit of variety, a bit of agency, and a bit of cinematic verisimilitude over gritty realism, rule away!

To answer the question, however, the purpose for the bonus is to increase mean damage output: but not to increase mean damage output so much as a two-handed weapon would provide. When fighting with two weapons, thus, a bonus to the attack roll will offer a moderate increase to damage. Assuming standard THAC0 ranges or attack matrices, the chance of scoring a hit against various armor values are as follows, where the first percentage is wearing the armor, only and the second percentage is wearing the armor and carrying a shield:

		Chance To Hit
Ftr. Tier	THAC0	Clothing		Leather		Mail		Plate
1-3	19	55%	50%	45%	40%	35%	30%	25%	20%
4-6	17	65%	60%	55%	50%	45%	40%	35%	30%
7-9	14	80%	75%	70%	65%	60%	55%	50%	45%
10-12	12	90%	85%	80%	75%	70%	65%	60%	55%
13-15	10	95%	95%	90%	85%	80%	75%	70%	65%

This will afford damage per round of combat as follows, assuming variable damage for weapons, again with the first damage per round value equating to the damage per round against that armor exclusively and the second equating to damage per round against that armor plus shield:

		Damage per Round, D4
Ftr. Tier	THAC0	Clothing		Leather		Mail		Plate
1-3	19	1.375	1.25	1.125	1	0.875	0.75	0.625	0.5
4-6	17	1.625	1.5	1.375	1.25	1.125	1	0.875	0.75
7-9	14	2	1.875	1.75	1.625	1.5	1.375	1.25	1.125
10-12	12	2.25	2.125	2	1.875	1.75	1.625	1.5	1.375
13-15	10	2.375	2.375	2.25	2.125	2	1.875	1.75	1.625
		Damage per Round, D6
1-3	19	1.925	1.75	1.575	1.4	1.225	1.05	0.875	0.7
4-6	17	2.275	2.1	1.925	1.75	1.575	1.4	1.225	1.05
7-9	14	2.8	2.625	2.45	2.275	2.1	1.925	1.75	1.575
10-12	12	3.15	2.975	2.8	2.625	2.45	2.275	2.1	1.925
13-15	10	3.325	3.325	3.15	2.975	2.8	2.625	2.45	2.275
		Damage per Round, D8
1-3	19	2.475	2.25	2.025	1.8	1.575	1.35	1.125	0.9
4-6	17	2.925	2.7	2.475	2.25	2.025	1.8	1.575	1.35
7-9	14	3.6	3.375	3.15	2.925	2.7	2.475	2.25	2.025
10-12	12	4.05	3.825	3.6	3.375	3.15	2.925	2.7	2.475
13-15	10	4.275	4.275	4.05	3.825	3.6	3.375	3.15	2.925
		Damage per Round, D10
1-3	19	3.025	2.75	2.475	2.2	1.925	1.65	1.375	1.1
4-6	17	3.575	3.3	3.025	2.75	2.475	2.2	1.925	1.65
7-9	14	4.4	4.125	3.85	3.575	3.3	3.025	2.75	2.475
10-12	12	4.95	4.675	4.4	4.125	3.85	3.575	3.3	3.025
13-15	10	5.225	5.225	4.95	4.675	4.4	4.125	3.85	3.575

The above excludes the mismatched weapons provision for the one-in-twenty chance of altered damage range for a hit; as that makes for much more complex to calculate math.

Thus, a level 4 (tier two) character striking a target with chainmail armor will - wielding a one handed sword that deals d8 damage - inflict an average of 2.025 damage per round or - wielding a two-handed sword that deals d10 damage - inflict an average of 2.475 damage per round: a net difference of 0.45 damage per round: or about 18%. Knowing, however, that shields separate armor class by 1 point and that each tier of armor is separated by two points, this provides us a linear progression: to compare how much damage you would have with a +1 bonus to hit, you can shift your gaze left one cell in the above tables. So, comparing a level 4 (tier two) character striking a target with chainmail, again, will still inflict an average of 2.475 damage per round using a two-handed sword, but using a one-handed sword at a +1 bonus to hit will instead inflict an average of 2.25 damage per round - the equivalent of striking leather armor with a shield - cutting the delta in half to 0.225 damage: or about 9%.

Using a d6 weapon, the difference compared to a two-handed sword is slightly less profound: 1.575 damage per round versus 1.75 damage per round with a +1 bonus to hit, compared to 2.475 damage per round with a two-handed sword, a 0.9 (~36%) and 0.725 (~29%) difference in damage output: or, about 7% improvement in the difference between the two. However, if you instead compare the d6 weapon against a d8 weapon - say, a two-handed battle axe - the change looks more familiar: 1.575 improves to 1.75 versus the two-handed axe at 2.025: 0.45 damage delta per round versus 0.275 damage delta per round: a difference of 0.175, or about 9%.

At each level of die progression, this is consistent, with +1 bonuses to hit resulting in an improvement to the damage per round as follows:

	Pct. Damage Delta per +1
Ftr. Tier	Clothing		Leather		Mail		Plate
1-3	9.09%	10.00%	11.11%	12.50%	14.29%	16.67%	20.00%	25.00%
4-6	7.69%	8.33%	9.09%	10.00%	11.11%	12.50%	14.29%	16.67%
7-9	6.25%	6.67%	7.14%	7.69%	8.33%	9.09%	10.00%	11.11%
10-12	5.56%	5.88%	6.25%	6.67%	7.14%	7.69%	8.33%	9.09%
13-15	5.26%	0.00%	5.56%	5.88%	6.25%	6.67%	7.14%	7.69%

Interestingly, the value of the +1 is higher at lower levels versus higher AC and is lower at higher levels, in general, but also lower relatively at higher levels: an interesting data point being that no improvement at all occurs between a top-tier fighter striking a character with clothing only versus clothing and a shield, highlighted in italics: a phenomenon occurring because the fighter has, at that point, to roll a 2+ to hit clothing or clothing and shield, so a bonus to hit offers no benefit. But this is in scope for a different discussion.

Dice d6 and d8 being the most common among one-handed weapons, comparing d6 or d8 at a +1 bonus to each other and versus d10 results in the following breakdown, where the number represents the difference between damage per round of the higher die (the two-handed weapon) versus the lower die at plus one (the one handed weapon being used while two-weapon fighting):

Ftr. Tier	Net Damage: D6 at +1 vs D8 at +0
1-3	-0.325	-0.275	-0.225	-0.175	-0.125	-0.075	-0.025	0.025
4-6	-0.425	-0.375	-0.325	-0.275	-0.225	-0.175	-0.125	-0.075
7-9	-0.575	-0.525	-0.475	-0.425	-0.375	-0.325	-0.275	-0.225
10-12	-0.675	-0.625	-0.575	-0.525	-0.475	-0.425	-0.375	-0.325
13-15	-0.95	-0.725	-0.675	-0.625	-0.575	-0.525	-0.475	-0.425
	Net Damage: D6 at +1 vs D10 at +0
1-3	-0.825	-0.725	-0.625	-0.525	-0.425	-0.325	-0.225	-0.125
4-6	-1.025	-0.925	-0.825	-0.725	-0.625	-0.525	-0.425	-0.325
7-9	-1.325	-1.225	-1.125	-1.025	-0.925	-0.825	-0.725	-0.625
10-12	-1.525	-1.425	-1.325	-1.225	-1.125	-1.025	-0.925	-0.825
13-15	-1.9	-1.625	-1.525	-1.425	-1.325	-1.225	-1.125	-1.025
	Net Damage: D8 at +1 vs D10 at +0
1-3	-0.275	-0.225	-0.175	-0.125	-0.075	-0.025	0.025	0.075
4-6	-0.375	-0.325	-0.275	-0.225	-0.175	-0.125	-0.075	-0.025
7-9	-0.525	-0.475	-0.425	-0.375	-0.325	-0.275	-0.225	-0.175
10-12	-0.625	-0.575	-0.525	-0.475	-0.425	-0.375	-0.325	-0.275
13-15	-0.95	-0.675	-0.625	-0.575	-0.525	-0.475	-0.425	-0.375

Again, some interesting data points occur, where tier-1 fighters will deal more damage per round to an extremely high AC, highlighted in italics - but again, speculation for another time, as without doubt, we are commonly sick of looking at tables by now.

Why not simply attack twice? Attacking twice is the de-facto standard for most two-weapon rules. Commonly, to mitigate the damage increase, there is a corresponding accuracy penalty: -4 in some systems, -2 in others, or sometimes mixed penalties based on whether you're attacking with the primary hand or the off hand. However - in all cases - extra attacks slow down play. Rolling two attacks, adjudicating two damage rolls, it takes twice as long on a player's turn: a problem that gets exponentially more noticeable later, if working in a system that grants extra attacks based on level progression. Although you can mathematically make rolling two attacks add up, average out, the same way this rule does - in the interest of keeping the game as sleek and streamlined as possible, I try to eschew extra rolls if I don't need them.

Why the "parry" AC? The objective of the rule is to produce a middle ground. A two-weapon fighter should, as explained above, inflict more damage than a fighter with one weapon but less damage than a fighter with a large two-handed weapon. Similarly and conversely, a two-weapon fighter should have better defense than a fighter with a large two-handed weapon but worse defense than a fighter with a shield. This is reflected in the parry action, the defensive stance: a defensive boost at the cost of the offense, but not so useful as having a shield would be.

To support this, consider the table above indicating likelihood of hitting based on level and armor. Inverting the perspective, this can likewise be used as an indicator for getting hit. That is, if you are wearing chainmail, a low level (tier-1) attacker will deal ~14.29% damage less to you per round if you don a shield as well. This amounts to about the following, in terms of damage per round less than a character would have taken, per -1 to a character's armor class:

	d4	d6	d8	d10
Dmg. Delta:	-0.125	-0.175	-0.225	-0.275

As such, a character with 10 hit points wearing leather armor will, if attacked by a tier-1 attacker using a 1d8 weapon, drop on the 5th round of combat: having taken 2.025 damage per round. This same character, if using a shield (or gaining equivalent bonus to AC in melee by fighting defensively with two weapons) would drop to the same opponent instead on the 6th round of combat: having taken an average of 1.8 damage per round, instead: the result of the opponent rolling more misses.

On a smaller weapon, this is proportionally less pronounced: the same character being attacked by the same tier-1 attacker using a 1d6 weapon instead of 1d8 would drop on the 7th round of combat, taking 1.575 damage per round; compared to dropping on the 8th round of combat after taking 1.4 damage per round on average. With a larger weapon, 1d10, the character would drop on the 5th and 6th rounds, respectively: same as a 1d8 weapon, to a tier-1 attacker.

Parrying offers the same protection of a shield in melee only - but to maintain the balance - leaves the two-weapon fighter vulnerable to missile attacks.

How about Shields Shall Be Sundered? Up to you: if you want to allow a two-weapon fighter in a parry stance to sunder his weapon to avoid a hit? Run it! And tell me how it goes!

May the dice smile on your ventures!

Public domain art lovingly pilfered from OldBookIllustrations.com in October of 2020 and adapted for thematic use. Attributions in alt text.