Sunday, November 22, 2015
The die roll value required for an attack to hit an armor class of zero, or "THAC0," is the signature combat mechanism of the second edition of Advanced Dungeons & Dragons. Revered by some and reviled by others, THAC0 replaced the combat matrices of first edition AD&D with pre-calculated values intended to be faster and more intuitive. Astute observers have long noted foreshadowing of a THAC0 system sprinkled throughout some first edition AD&D texts. It is however less widely known that THAC0 was in use with the original Dungeons & Dragons game, prior to the publication of the Players Handbook or Dungeon Masters Guide. The excerpt above is from Alarums & Excursions #31 (February 1978), and it describes the contemporary use of THAC0, including the acronym itself.