Marlon Brando initially refused to go on a press tour to promote the film. The studio threatened him, as he was contractually required to promote the film, so Brando made an appearance at one press conference at which he said, "You will be unable to proceed in life unless you see Morituri." The studio released him from doing more press appearances after this sarcastic statement.
Initially, Trevor Howard was reluctant to work alongside Marlon Brando again, following their strained relationship while filming "Mutiny on the Bounty" (1962). However, since Howard only had a one scene appearance, he finally agreed.
Esther, played by Janet Margolin, uses the surname Goddard instead of her own surname Levy in order to conceal her Jewish ethnicity. This reflects the real life situation of Hollywood actress Paulette Goddard who changed her name from Marion Levy in order to downplay her own Jewish ethnicity.
The Morse code heard at the end of the movie says "CQ CQ CQ DE SS INGO (then code for a new line: BT) CARGO SHIP OUT OF . . . " (code fades as music rises). The repeated CQ's are an invitation to whoever may be listening to reply. [DE is code shorthand meaning "from"]
This movie bombed at the box-office upon initial release. It was a financial disaster for Twentieth Century-Fox, coming on the heels of Cleopatra (1963), another high-profile drain on the studio. The film brought in only $4,045,000, less than half of it's break-even amount of $10.5M according to studio records. It is believed that the film's title was not understood by the public. As such, when re-released, the film was re-named "Saboteur: Code Name Morituri."