Michael Douglas' uncredited role (and theatrical movie debut) came about when an Israeli actor refused to perform a driving stunt, claiming it was too dangerous. Kirk Douglas, trusting his son's skill as a driver, enlisted Michael to fill in on the spot.
Writer, Producer, and Director Melville Shavelson and Kirk Douglas fought throughout the shoot. At one point, Shavelson even walked off the set, leaving his assistant to take over for the day.
This was Topol's first American picture. Five years later he would attain U.S. stardom as Tevye in the film version of Fiddler on the Roof (1971).
During filming in August 1965, John Wayne enraged Writer, Producer, and Director Melville Shavelson with his views on the Watts Riots.
This is the second of 3 consecutive films John Wayne & Kirk Douglas made together: In Harm's Way (1965), this film in 1966, and The War Wagon (1967).