This was the only time that David Niven ever smoked cigarettes on-screen. Niven was a life-long non-smoker.
During shooting, Gregory Peck and David Niven became close friends, bonding initially over Peck's ability to consume vast quantities of brandy, which the actors used to "stay warm" while filming in a cold studio tank, without muffing a line. Their families visited each other frequently in later years, and Peck would deliver the eulogy at Niven's funeral.
Although in the plot, Mallory is supposed to be fluent in German, Gregory Peck could not speak the language, and so his German lines are all dubbed by Robert Rietty. Peck was also dubbed when speaking Greek.
David Niven initially felt that he was badly miscast in the offbeat role of a Corporal, but he later said he considered it to be one of his best performances, despite being too old for the part.