OSR Armour

Apparently people are really ideological about the ascending/descending armour class issue. I never understood this. I can understand why some people prefer ascending armour class and positive to hit bonuses to THAC0, on the basis that addition is easier than subtraction, I guess, but on my Basic D&D character sheet, I always wrote down the score needed to hit each armour class. As a player anyway this is even easier than ascending armour classes and bonuses to hit – you just add your Strength bonus to your roll and glance at the table to see whether you hit an opponent with a given AC. For example (for level 1 characters in Basic D&D):

To hit AC:	9	8	7	6	5	4	3	2	1	0	-1	-2	-3
Roll Req’d:	10	11	12	13	14	15	16	17	18	19	20	20	20

To avoid blundering into the ascending/descending AC holy war (seriously people), and also to remain compatible with AD&D’s different base AC I suppose, many OSR/DIY D&D modules now present monster and NPC armour class not with a number, but with an armour type.

This is quite neat. Let’s look at the basic armour types from Basic D&D and their numeric armour classes from Basic, AD&D, d20 and 5e (slightly simplified):

Armour Type	Basic	AD&D	d20	5e
Unarmoured	9	10	10	10
Leather	7	8	12	11
Chain mail	5	5	15	16
Plate mail	3	3	18	18
Shield	-1	-1	+1	+2

Not only are there different armour classes between each generation of D&D as shown in the table above, but the gaps between armour classes is also inconsistent. In trying to provide a “look up” table similar to the kind written on your character sheet in Basic D&D with rolls required to hit for each armour type listed, I have by coincidence settled upon the d20 AC numbers (they tend to be either the same as the roll required in Basic or between that number and the 5e AC):

Armour Type	Roll Required (1d20 + To Hit Bonus)
Unarmoured	10
Leather	12
Chain mail	15
Plate mail	18
Shield	+1

The “To Hit Bonus” is the Strength (melee) or Dexterity (ranged) modifier plus the proficiency bonus (5e), base attack bonus (d20), or 20 – your THAC0 (in TSR versions of the game).