The film chronicles Continental Shelf Station Two, or "Conshelf Two", the first ambitious attempt to create an environment in which men could live and work on the seafloor.

Men on the bottom performed a number of experiments intended to determine the practicality of working on the sea floor and were subjected to continual medical examinations.

Funded in part by the French petrochemical industry, the Conshelf Two experiment was originally intended to demonstrate the practicality of exploitation of the sea using underwater habitats as base stations.

Memorable sequences involve men cavorting with fishes, an underwater chess game and the diving saucer reaching depths of 300 meters, encountering new and unique forms of life.

Cousteau, taking great offense, went on to demonstrate how he and his son Philippe produced the shot with a combination of ropes and small underwater motorized vehicles.