Mannahnin
Scion of Murgen (He/Him)
And the 1e AD&D attack tables contained a note that as an optional rule you could "smooth" the progression of Fighter attacks to be a 1pt improvement per level instead of 2 points every two levels. And of course this was itself a smoothing of the progression from OD&D and the Basic line, where the Fighter's attack progression jumped three points at 4th level.* Give or take a point – One of the differences between 1e and 2e was that 1e had attack tables for each class where you'd cross-reference level with the target's AC to get the number you need to roll to hit, while 2e used a mathematical formula to generate a THAC0 value. The two mostly worked out the same, but the fighter attack table advanced 2 points per 2 levels, while the THAC0 formula advanced 1 point per level. Monster THAC0 remained at 2/2 in 2e, probably to maintain continuity with old monster descriptions.
In an amusing historical revelation, it turns out that the original concept was a 5% (1pt) improvement every level of advancement, but that they altered it for the 1974 publication, apparently in part because of space limitations for the tables!

Why Did Armor Class Descend from 9 to 2?
One of the great riddles that has vexed D&D players for generations is this: why did armor class in original D&D descend from 9 to 2 inst...