The armor in the climactic battle with the Nazis was authentic medieval armor, previously used in Camelot and El Cid. When any item of armor was to be destroyed, exact fiberglass replicas were created and used.
The castle in the background of the town is real and situated in Dorset, England. Both the castle and the town where it resides are called Corfe Castle, where many Thomas Hardy adaptations have been filmed since.
Walt Disney bought the film rights to the two Mary Norton books in the early 1960s, around the same time as work on Mary Poppins. When "Poppins" author P.L. Travers stonewalled on the movie rights negotiations to her books, most of the story development along with many of the songs for this film were written at this time. Had Travers not granted the film rights to her own books, Bedknobs and Broomsticks would have been made instead.
The Sherman Brothers wrote two songs that never made it past preproduction despite Richard M. Sherman's protests. The first, "The Fundamental Element," had Miss Price explain her kindly philosophy to the children after turning Charlie into a rabbit. The second was a Music Hall pastiche called "Solid Citizen," which Miss Price would have sung to distract King Leonidas and get the magic star; ultimately, the soccer game replaced it. Both of them went unheard until demos performed by Richard M. Sherman appeared on the CD soundtrack reissue.
The film premiered at the Radio City Music Hall in New York City, a booking which had serious repercussions. The Music Hall's Christmas stage show ran so long, whatever film premiered there had to be under two hours. After much debate, Disney cut the film down to 117 minutes rather than cancel the booking. After seeing the same thing happen to The Happiest Millionaire and The One and Only, Genuine, Original Family Band, the Sherman Brothers decided not to renew their contract with Disney. In 1995, Scott MacQueen, who headed Disney's restoration department, discovered that two of the cut songs, "With a Flair" and "A Step in the Right Direction" were still on the soundtrack album and quoted throughout the underscore. When he learned the extent of the film's edits, he persuaded Disney to reconstruct the longer cut.
While the name of the King of Naboombu is never spoken in the film or mentioned in the credits, all merchandise and peripheral material related to the film refers to him as "King Leonidas," named after the Spartan king who died at the Battle of Thermopylae in 480 B.C.
While Julie Andrews initially turned down the role of Miss Price, she eventually reconsidered, believing she owed her film career to the Disney studio and wanting to work there again. However, when she told the studio she changed her mind, Angela Lansbury had already accepted the part, having signed her contract for the role on Halloween of 1969.
Angela Lansbury hated what she called "by the numbers" acting in this film. Due to the heavy special effects, the entire film had to be storyboarded in advance, shot for shot. Lansbury found this approach constraining to her performance, as it meant every moment was pre-determined and the actress wasn't free to explore the character naturally.
According to the Laws of the Game, as authorized by the International Football Association Board, no goal should have been awarded during the soccer match. The referee would properly have stopped play at the point where the ball burst or became deflated (Law 2), if not earlier for substandard field surface or goalposts (Law 1), short-sidedness (Law 3), insufficient equipment (Law 4), severe injury (Law 5), advantage gained by being in an offside position (Law 11), or any of various fouls and misconduct (Law 12), including but not limited to: dangerous play, dissent, unsporting behavior, serious foul play, and leaving the field of play without permission.