It is an account of scientific voyages taken by Cousteau, the world-famous oceanographer, aboard his ship, the Calypso. Cousteau and his crew roam far and wide, exploring the Mediterranean Sea, the Red Sea, and the Indian Ocean. Cousteau's men demonstrate the effectiveness of scuba gear over old-timey diving suits. They take samples of coral reefs and the fish that live therein. They observe sea turtles laying their eggs on a remote island. They map the sea floor with sonar. They even manage to find and explore a sunken World War II freighter. They use underwater cameras to take spectacular footage.
They also kill a lot of animals. A lot. It's one thing when they harvest for breakfast the fish that leap up onto the deck. It's maybe defensible when divers from the Calypso snatch up lobsters from down below and bring them to the ship to eat. But it's not so defensible when Cousteau's men take joyrides on sea turtles underwater, as the turtles struggle to make it to the surface and breathe. In another scene Cousteau's crew elect to get a representative sample of the fish that lurk in coral reefs by dynamiting the reef and harvesting all the fish that are killed. In the worst scene, Cousteau's crew massacres a whole school of sharks that are only there to feast on the fresh corpse of a baby sperm whale. The good news is that Cousteau learned his lesson and for the rest of his career would take a leading role in the environmental movement.
- For Science!: The odd thing is that Cousteau obviously recognizes that blowing up a coral reef to kill all the fish in it is a bad thing. He calls using dynamite to fish "vandalism". But he still uses dynamite to get his samples of fish, for science.
- Friendly, Playful Dolphin: A school of porpoises tags along with the Calypso for a while, leaping out of the water, getting way too close for Cousteau's comfort.
- In Medias Res: No opening scene where voiceover introduces what the story's about. Instead we open with a pretty spectacular shot of Cousteau's divers going deep, underwater torches in hand.
- Narrator: Mostly by Cousteau himself, narrating the voyages of the Calypso.
- Nature Documentary: A surprisingly violent one.
- Scenery Porn: Shockingly beautiful underwater photography, starting with the first scene, in which Cousteau's divers swim into the depths in formation, holding sticks that burn underwater to light their way.
- Silence Is Golden: Well it is called The Silent World. One of the most amazing sequences, the exploration of the sunken Allied freighter ship, lasts a full 10 minutes, without a word of dialog being stolen.
- Title Drop: At both the beginning and the end the narration describes the depths of the ocean as "a mysterious realm, the silent world."
- Turtle Power: Sea turtles. When underwater, the divers use sea turtles as transportation, holding onto them and riding as the turtles struggle to break free and get to the surface to breathe. On land, Cousteau's men ride around on the turtles and use them as stools. We also see a mama turtle laying a prodigious amount of eggs, followed by baby turtles waddling across the beach to the sea.