I lost 5 points in a pub trivia contest for believing Song of the South
(1946) was the first film to combine live action and animation.
The correct answer is Anchors Aweigh
(1945), starring Frank Sinatra and Gene Kelly. The animation comes in form of Jerry, the bloody mouse from the Tom and Jerry
The screaming pain of losing five points still echoes within me.
I'm not sure even this is correct. Live action and animation had been combined in silent movies, e.g. Gertie the Dinosaur.