This episode of "The Magical World of Disney" is essentially a giant commercial encouraging folks to go see the studio's newest epic, "20,000 Leagues Under the Sea". At times, it seems to talk about other things....but the bulk of this one is a big advertisement.
The beginning of the show looks like it's just a lesson on the history of underwater diving. But then after a lecture and some cartoon footage, the episode begins talking at length about the movie and how wonderful it is.
To me, this was probably more interesting than to the average person because they talked a lot about scuba and showed some very early and primitive examples....and I am a diver myself. Otherwise, it's not among the best examples of this old show because its intent clearly is less on entertaining the folks at home but convincing them to go to the theater to see the film.