Stephen Boyd nearly drowned while shooting this film. He was saved by co-star David Wayne, according to Boyd in a December 11, 1960 appearance as a Mystery Guest on What's My Line? (1950).
Despite the fact that Dublin was chosen because of its gray skies and regular rain showers, the weather during the shoot was unseasonably good, and Dublin fire crews were needed to hose down key locations to make the streets look wet.
Darryl F. Zanuck behaved very badly on the set, according to director Richard Fleischer. He was not only there for scenes involving his girlfriend Juliette Gréco, but for the other actors as well--including rehearsals. He sat in his chair smoking a cigar, but not looking up from the script ON the set, something that Fleischer had never seen before or since. If an actor had to move, he had to move around Zanuck.
Despite the fact that Stephen Boyd was born in Glengormley outside Belfast, this was the only time he appeared in a movie shot in Ireland.
Second-unit director Elmo Williams screwed up a scene during shooting, filming an oversized colonial helmet for an actor. The only way to save him from producer Darryl F. Zanuck's wrath was for director Richard Fleischer, an old friend of Williams, to shoot many other scenes again, delete, burn already shot sequences with the oversized helmet; all this without saying anything to Zanuck. Years later, during shooting of The Longest Day (1962), part of which Williams directed, he and Zanuck became good friends. However, Zanuck and Fleischer eventually got into a long and bitter feud, and when it came time for Williams to choose between the two, he chose Zanuck, conveniently forgetting that it was Fleischer who saved his neck on this picture.