While filming Os Bravos Morrem Lutando (1965), Brad Dexter had apparently rescued Frank Sinatra from drowning when he got into difficulty swimming. As a thank-you, Sinatra agreed to star in this film when Dexter was starting out as a producer; however, it was reported that he was very difficult throughout the filming and gave Dexter and director Sidney Furie many headaches.
The gun prop used in this film was later converted to become Han Solo's blaster in Star Wars: Episódio IV - Uma Nova Esperança (1977).
Filmed on location in London and Copenhagen.
Final film of Nadia Gray .