Richard Fleischer was surprised at being considered for the director's chair for this film, as he was the son of Disney's biggest competitor, Max Fleischer. He approached Walt Disney to inquire if Disney knew who he was. Disney told him that he was well aware of who he was and hired him because he thought he was the best man for the job. Richard Fleischer also asked his father if he minded having his son working for his rival but Max Fleischer made no objection and even asked Richard to tell Disney that he thought he had made an excellent choice for his director!
This production was so large that Disney had to use facilities at other studios. This included Universal International (exterior sets redressed for the opening scenes) and 20th Century Fox (large exterior tank for the larger models).
The skiff was made of wood, painted to look like metal, and had to be weighted with sandbags to look heavy in the water. When towing it to the cannibals' island, the crew took the sandbags out to make their job easier, and they forgot to put them back in. When filming the scene where Ned and Conseil get in the boat to row away from the cannibals, Kirk Douglas expected the boat to be low in the water. He didn't lower the oars far enough to catch the water, and when he started to row, he fell on his back. Director Richard Fleischer thought the shot was so funny he left it in the film. When Ned starts to row, he clearly tips back, and his legs shoot up in the air.
In 1969, Captain Nemo's pipe organ, which had been on display in Disneyland, was redressed and now resides in the ballroom of Disneyland's Haunted Mansion. A duplicate was constructed for the ballroom of Walt Disney World's Magic Kingdom Haunted Mansion, which opened in 1971, and over a decade later another duplicate was built for Tokyo Disneyland.
When Disney executives saw some underwater scenes their photographers had filmed in the new VistaVision wide-screen format, they decided to make "20,000 Leagues Under the Sea" and incorporate some of the shots in it.
Actors portraying the cannibals chasing Ned Land painted humorous messages on their foreheads (not legible on-screen). In particular, one actor wrote "Eat at Joe's" while another actor behind him wrote "I ate Joe".
During the underwater shooting of the Treasure Chest scene, an unscripted nurse shark approached Ned, Conseil and the camera crew. All underwater personnel, as seen in Disney's Wonderful World of Color Sunday Night television episode highlighting the upcoming film, attempted to warn the shark off, but the interruption was considered so exciting that portions were left in the final film.
The world's first functional replica of Captain Nemo's diving helmet, built by Pat Regan of Vulcania Submarine, Hawaii, is on display in the Florida Keys History of Diving Museum in Islamorada, along with items from the film. He has also restored the one known surviving 'crown' or crewman diving helmet to operational condition.
According to Kirk Douglas in his autobiography, "Ragman's Son", the scene at the beginning of the film where Ned Land strolls up (with a beautiful girl on each arm) to the lecturing sailor - and the ensuing fight - was written into the film at his request. At the time this film was shot, Douglas was in the prime of his career and very concerned about promoting and preserving his reputation with the movie-going public as both a dashing ladies man and a "macho" actor known for tough, physical roles that showcased his image as an action hero (fight scenes and so forth). When he first read the first draft script for this film, he was somewhat disappointed to find that his character Ned Land made no appearances with any women whatsoever, had no real rousing fight scenes, other than the battle with the squid, and spent most of the movie talking instead of being in action. Having expressed these concerns both to Walt Disney and director Richard Fleischer, the San Francisco street scene at the beginning of the film - featuring his character involved with two beautiful women in addition a rousing action/fight scene - was added especially for him (in at least two later films Douglas also made sure his character would be seen with two beautiful women at the same time and be involved in plenty of rough & tumble action: The Vikings [also directed by Fleischer] and The War Wagon.
This was Walt Disney's first feature using the new CinemaScope process, as well as one of the first productions outside of 20th Century-Fox use that anamorphic wide screen process. At the time, Bausch & Lomb had not been able to manufacture enough anamorphic lenses to meet the demand, so the Disney studios needed to lease the single available CinemaScope lens from 20th Century-Fox. This prevented multiple units from shooting at the same time, which not only contributed to the lengthy production schedule, but also--since Disney wanted the best possible value for the CinemaScope lens rental--explains the almost complete absence of close-up shots in the movie.
In the opening credits, the title banner does not have a comma between the first and second zeroes ("20000 Leagues Under the Sea"), although a comma does appear on the poster and all related print advertisements.
The climactic squid battle on the Nautilus was originally shot with a serene sunset and a calm sea. Director Richard Fleischer was troubled by the look of it because the cams and gears that operated the squid could easily be seen, making it look obviously fake. Walt Disney visited the set one day and Fleischer told him about the problem. Disney came up with the idea of having the squid battle take place during a fierce storm (another story is that it was actually screenwriter Earl Felton who came up with the idea). The scene was reshot that way and is considered by many to be the highlight of the film.
Until the late 1960s, many of the sets representing the interior of the Nautilus were used as an attraction at Disneyland. This included the chart room, the salon, with organ, and one of the observation windows. The squid from the movie was fastened over the observation window and was animated so that the beak would emerge, snap several times, and then retract. When the building housing the "20,000 Leagues" display was needed for a newer attraction, the sets were removed and many were destroyed.
This was the first new full-length Disney film released by Buena Vista, Disney's new in-house distributor. Previous Disney films had been released by RKO, and re-releases of old Disney films were handled by Buena Vista from 1954 onwards.
This was the one of the first Disney films shown in a two-hour time slot on television (although very slightly edited). Most previous telecasts of Disney films, all shown on the anthology series Walt Disney's Wonderful World of Color (aka "The Wonderful World of Color" and "The Wonderful World of Disney") had either featured the films edited down to fit a one-hour time slot or broken them up into two or more one-hour segments shown over a period of several weeks.
Walt Disney originally considered making this film as an animated feature; the detailed pre-production sketches by artist Harper Goff, as well as Goff's enthusiastic suggestion that it be done as live action feature, convinced him otherwise.
During his 'Whale of a Tale' tune, two of the girls Ned sings about are named 'Mermaid Minnie' and 'Typhoon Tessie'. Minnie and Tessie were the two girls on his arms at the beginning of the film - you can hear him shout their names at one point during the street brawl.
Although Percy Helton was billed in the opening credits, his role (as a coach driver) was almost entirely eliminated; in the release version, he appears in only one shot (no dialogue), waiting for passenger Lukas to finish his interview with the reporters.
Cast members carried herring in their pockets to reward Esmerelda the seal after their scenes with her. Director Richard Fleischer was especially amused when the distinguished James Mason had to reach into his pocket after a shot. Fleischer said the cast smelled like the Fulton Fish Market.
Richard Fleischer was the son of Max Fleischer, head of a rival animation studio. Richard was reluctant at first to take the job until his father encouraged him to do so, sending with him his compliments to Walt Disney on his taste in directors.
In this film, the power source for the Nautilus is clearly implied as nuclear power. This is intimated by, among other things, the nuclear explosion of Nemo's island at the end of the film. In the original Jules Verne novel, however, Nemo explains to the professor a system which most resembles a fuel-cell battery originally powered by coal burning. Disney's decision on this matter was clearly influenced by the discovery of nuclear energy (i.e. the atomic bomb) only 10 years before this film. Meanwhile, in the 21st century, it is predicted that cars will run on fuel cell batteries and the original power source will be coal-fired power plants, which is ironically a return to Verne's ideas from 150 years ago.