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:9876543210-1-2-3
Roll Req’d:10111213141516171819202020

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.

Example from DIY D&D remake of Palace of the Silver Princess,

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 TypeBasicAD&Dd205e
Unarmoured9101010
Leather781211
Chain mail551516
Plate mail331818
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 TypeRoll Required (1d20 + To Hit Bonus)
Unarmoured10
Leather12
Chain mail15
Plate mail18
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).

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