"The multiplane camera is a special motion picture camera used in the traditional animation process that moves a number of pieces of artwork past the camera at various speeds and at various distances from one another. This creates a three-dimensional effect, although it is not actually stereoscopic.
Various parts of the artwork layers are left transparent, to allow other layers to be seen behind them. The movements are calculated and photographed frame-by-frame, with the result being an illusion of depth by having several layers of artwork moving at different speeds - the further away from the camera, the slower the speed. The multiplane effect is sometimes referred to as a parallax process.
The trailer for Walt Disney's Snow White 1937:
The Multiplane Camera explained.
Walt Disney Would Famously Bring HIs Animation Film Skills To National Television When He Helped Sell The Public On The Idea of Space Travel. Interesting how Disney teamed with a SS Nazi to do so. So goes the history of Hollywood and the military.
Operation Paper Clip Brings The Nazis to America