This was the only cinema film to be directed by S. Lee Pogostin, a well-known television writer. James Coburn later claimed in interviews that Pogostin was the cause of the film's considerable box-office failure, as he had refused to alter his extremely wordy script and then proved to have little idea of how to direct a film. According to Coburn, the actors more or less directed themselves whilst cameraman Jack Hildyard handled the technical details.
When Cunningham is in Brussels a fight breaks out in the bar over the issue of whether the official language of Belguim should be French or Flemish (a Dutch dialect). Belgium is a country roughly divided half-and-half between the two languages.
This film broke Sterling Hayden's five-year absence from movies. Since the early fifties he'd been working almost every year. It lessened in the late fifties and early sixties. Then, after this movie, his roles became frequent again: but as a character-actor and not always a lead or even co-star.
Filmed on location in Brussels, Belgium, Tangiers, Morocco, and Madrid and Torremolinos in Spain.
Italian censorship visa # 53929 delivered on 13 June 1969.