Sink Or Swim.

Champion Johnny Weismuller teaches a class of girls the fundamentals of the American Crawl—first they learn on land to kick without bending their knees, then the arm movements follow. Breathing is important, it's done in exactly the reverse of what health and good manners dictate ashore. Then the entire class is taken into, and beneath the waves, to study and copy how easily the ducks, the turtles, and the fish can do the job.