In his autobiography "Sun and Shadow", Jean-Pierre Aumont, who played Jacques, spoke of scheduling conflicts between Spencer Tracy and Frank Sinatra: "[Tracy], a genial man who was not well at the time, couldn't work past the morning. The problem was that Sinatra would only work in the afternoon. In the morning he hired a private plane and hopped from island to island trying to convince the startled inhabitants to vote for [John F. Kennedy] in the next presidential election. Around two o'clock he returned, exhausted, at the precise moment when Tracy was retiring for the day to his rooms. How, in these conditions, the scenes between Tracy and Sinatra were shot is a mystery to me."
The volcano in this film was built from scratch in farmland outside Fallbrook, California. Each shot required packing with hundreds of pounds of explosives and a carefully-orchestrated "eruption" to be filmed by the cameraman seated on the front skids of a helicopter. One eruption went off a little early and nearly took out the chopper, burning off the cameraman's eyebrows and some of his hair. Because the eruptions looked so good, this ersatz volcano provided stock footage for decades of other films, commercials, etc.
Richard Widmark has said that Spencer Tracy told him that a broomstick was used as Frank Sinatra's stand-in during Sinatra's absences, marking his position in a scene, the brush end representing Sinatra's head. Tracy had to act opposite it whilst a script girl read Sinatra's lines.
The meaning and relevance of this film's title is that its literary origins are said to have derived from a proverb that says, "It is hard for a man to be brave when he knows he is going to meet the devil at four o'clock". Moreover, in the film's story, the team of rescuer adventurers goes out to save lepers on the mountain after the volcano has erupted and the island evacuated. They must return by 4:00 o'clock the next day, which is the deadline for when the last schooner will depart the island.
Director Mervyn LeRoy, said of this film in his autobiography, "Mervyn LeRoy: Take One": " . . . what made it a problem was that the climactic scene involved a volcano, and that's the kind of thing you have to worry about and plan for with extreme care . . . It was done partly on a Hollywood sound stage, partly in the Hawaiian Islands. And we also used miniatures extensively. We built a mountain near La Jolla, on Gil Hodges' farm. Mostly, though, we shot in Lahaina, on the Hawaiian island of Maui. We built a lovely set there--an entire village, complete with a street, a church and even a jail. Even though we were shooting in one of the most beautiful places on earth, it was a tough picture."
Though Spencer Tracy had top billing on this picture and Frank Sinatra second billing, it's Sinatra's image that's centrally situated at the forefront of the movie's principal theatrical movie poster, not Tracy. BarBara Luna and Tracy are positioned secondarily behind Sinatra.
"Digitally Obsessed" said of this picture, "Even though they both began their careers at the movie studio that boasted the claim of "more stars than there are in the heavens" [MGM], it took nearly 20 years and a rival company [Columbia Pictures] to bring Frank Sinatra and Spencer Tracy together for their first and only collaboration."
"DVD Verdict" said of this movie, "Spencer Tracy and Frank Sinatra were already signed for the two lead roles, but there were problems coming up with a director, apparently because no one was particularly thrilled with the script. Finally, veteran Mervyn LeRoy was persuaded to take on the task and actually spent some time himself massaging the script into its final form. Filming involved some work on a Hollywood sound stage and the use of miniatures, but most of it took place in Lahaina on the Hawaiian island of Maui."
The picture's main poster connected it with two classic movies in its slogan that stated: "In the great high-adventure tradition of "The Guns of Navarone (1961)" and The Bridge on the River Kwai (1957)"." Notably, those two pictures were war movies and this film is not.
Kerwin Mathews wanted to welcome Katharine Hepburn, who had accompanied Spencer Tracy, to Hawaii by giving her a book about the history of the Island. Hepburn threw it into the ocean, saying" Who wants to know anything about this awful place?".