During the filming of the bicycle scene, a Krishna devotee approached all four Beatles with copies of a book about Hare Krishna, sparking the interest George Harrison would carry the rest of his life.
Film debut of Eleanor Bron.
In several early scenes, Klang and his stooges are using a "Mr. Whippy" ice cream truck as a hideout. American viewers might not be aware that Mr. Whippy is a real ice cream franchise, the equivalent of our own Mister Softee; it's based in New Zealand.
In the beach scene towards the end of the film, John Lennon had an appointment and could not be present. Another actor stood in for him.
In the deleted scene with Frankie Howerd and Wendy Richard, Frankie's character is "Sam Ahab", spelled backwards it's "Bahamas", where The Beatles eventually wind up.
In the final "I'm going to miss the sacrifice" scene where Klang's men, The Beatles, Ahme and the good police of the Bahamas are on the beach where they are rolling around in the sand fighting, a strange shot of a pair of very feminine legs and skin covered with sand is inserted for a flash of a second.
In the pub scene, the other three Beatles are persuading Ringo to have his ring finger amputated. Ringo refuses, insisting that he will miss the digit. Paul counters with, "You don't miss your tonsils!" Ringo actually underwent a tonsillectomy two months prior to filming.
In the scene where TNT is placed underground, one of the boxes says "EQUAL TO EXACTLY ONE MILLIONTH OF ALL THE HIGH EXPLOSIVE EXPLODED IN ONE WEEK OF THE SECOND WORLD WAR."
It is a popular belief that the first time John appeared in public wearing his trademark glasses was in film How I Won the War. This is not true; John can be seen wearing his granny glasses during the scene in which the Beatles are in disguise at an airport, waiting for a flight to the Bahamas. In an earlier scene at the Indian restaurant, John can be seen spooning the same pair - or same type - of glasses out of his soup.
One of the film's original taglines was, "Please do not reveal the beginning of this movie to your friends (they'd never believe it, anyway)". This is a spoof of the tagline from 'Alfred Hitchcock''s Psycho, which implored its audience, "Please do not reveal the ending of this movie to your friends (it's the only one we have)".
Originally, the Beatles were going to make a western picture. The story was going to be set in Texas and involved the four of them fighting over the affections of a cattle baron's daughter. There are even publicity photos showing them on horseback and wearing cowboy outfits. However the film shut down production and the Beatles ended up making this film instead.
The "ferocious man-eating tiger" which terrifies Ringo in the cellar of the pub is actually only a cub; it appears to be about ten months old. A real full-grown tiger would be MUCH larger. In addition to this, Ringo was also behind several inches of glass, separating between him and the tiger (this was mentioned in the special edition DVD).
The actors had 16 days, meaning 10 pages per day to memorize.
The Bahamas scenes, which are the final ones, were actually the first to be shot. The Alps scenes were filmed second, and the England scenes were filmed last. One scene which never appeared in the final film involves Ringo milking a cow in the back room. It was supposed to take place just before John takes a book from the shelf and sits down in his pit.
The Bahamas, which is where the "Another Girl" sequence was filmed, was actually rather cold during filming. This why all the Beatles except Paul are wearing long-sleeve shirts in what looks like very hot weather.
The Beatles were dissatisfied with this movie, saying that they "felt like extras in their own movie".
The Hindu god that Klang and his occult worships is "Kali" (Also known as Kali-Ma). Kali is the eastern equivalent to the "Grim Reaper". She is also the god worshiped by the occult in Indiana Jones and the Temple of Doom.
The horse that Paul is astride in the "Ticket to Ride" sequence is a Haflinger horse, which originated in the Austrian Alps.
The lockup scene was filmed at a psychiatric hospital in the Bahamas. Not long afterward, the band attended a dinner with the Minister of Finance, where John Lennon criticized the hospital's conditions.