Michael Douglas' movie debut.
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.
During filming in August 1965 John Wayne enraged director Melville Shavelson with his views on the Watts Riots.
Though not really trivia, it is there for all who view it to see, this film's opening prologue states: "The major events in this film actually happened. Some of them are still happening. The major characters actually lived. Many of them are still living. Although it was not easy." At the time of release, this statement was probably the case.