As one might guess from the premise, the film is utterly humourless. That’s not a bad thing, particularly in light of the existence of Stanley Kubrick’s already-mentioned film, which looks at the exact same issue with a similar character configuration, but through a satirical lens. The two films complement each other.
The tonal lack of cheerfulness is underscored (no pun intended) by the complete lack of music, the stark black and white photography, and the controlled editing with many close-ups and long takes. As a result, the film’s mood starts uncomfortable and suspenseful and grows increasingly tense as it becomes more and more unlikely that the bombers can be stopped. The actors, including Henry Fonda as the President and a young Larry Hagman as his translator, do their part not to let the audience off the hook with any expression or linereading that might break the tension.
I wasn’t alive back then, but I’m guessing this is what it must have felt like during the Cuban missile crisis and its aftermath, and Fail-Safe is a powerful warning to the two superpowers (but particularly the audience at home, in the United States) that Mutually Assured Destruction is not a game, but a highly dangerous policy with potentially deadly and unforeseen consequences.