It’s hard to make an easier mistake, in writing about history, than to proclaim anything as the first time anything was done. When you look closely at anything interesting or intricate you realize that it becomes difficult to say what, exactly, are the defining traits of the interesting happening, and you realize there’s almost always a prior case that’s at least as strong a candidate for “the first”.
This is why I bring up the Paul Terry Aesop’s Fables-series cartoon Dinner Time, released to theaters in September and October 1928, which comes in comfortably ahead of Steamboat Willie. This is an important point, as Dinner Time is unmistakably a full sound cartoon, and properly, predates the cartoon everyone thinks of as the first. It’s easy to see why Steamboat Willie so overwhelmed Dinner Time; while Dinner Time is mature in some ways — particularly, it’s staged much more as a sound picture, without written-out words or floating music notes or other holdovers of silent cartoons — it’s not as fun a cartoon as Steamboat Willie, and of course Disney would be a somewhat more significant corporate entity than the Fables Pictures, Inc, company proved to be.
It’s recorded in RCA Photophone, one of the four systems of synchronized-sound recording developed in the 1920s, and one that would be used through to the rise of stereo sound recording. It isn’t the first sound cartoon either: even if we limit the discussion to commercially released films, the Fleischer brothers made a series of Song Car-Tunes from 1924 to 1926 using the DeForest Phonofilm recording system, and I don’t doubt the search for “a” first would lead us into a fascinatingly complicated world of early technology.
(The Aesop’s Fables series itself started out as a set of animated stories with morals included, although either the versions I’ve found lost the moral or by this point in the series Terry had given up on the gimmick.)