When this film was made, there were about 100 stunt performers in the United States. About 80 of them worked on this film.
For the intermission of the premiere engagement at the Cinerama Dome in Hollywood, the filmmakers recorded messages supposedly sent over police radios describing what was happening to various characters. These messages were played not only in the auditorium during the intermission but at the concession stand and even in the restrooms.
Jack Benny's cameo role was originally offered to Stan Laurel, but Laurel turned it down. When his best friend and partner Oliver Hardy died in 1957, he pledged never to perform again. He kept that promise for the rest of his life. By the time this happened, a long shot of the character had already been filmed with a stand-in wearing Laurel's trademark bowler hat. This is why Benny is seen wearing a bowler hat despite never having worn one as part of his regular work.
The scene where Melville accidentally knocks the blowtorch into the stairs with the sledgehammer took 86 takes to get just right.
The film was so crammed with action that each leading actor was given two scripts: one for the dialogue and one for physical comedy.