This was the first ever movie to receive a rating from the MPAA in 1968.
This was Hammer Films' most profitable movie.
In a 2011 interview, Veronica Carlson talked about auditioning for the movie. She said she was modeling and Hammer studio head James Carreras saw a photo of her coming out of the waves in a white bikini on the front page of a tabloid newspaper and said he wanted her in his next movie. She auditioned with Barry Andrews, producer Aida Young, and director Freddie Francis. Then they had dinner afterward. She was very nervous and started worrying they were going to turn her down. To avoid being embarrassed, she thanked them for the meal and suddenly left. When she got home, her mother said the studio called saying they wanted her for the role.
Hammer stalwart Terence Fisher was due to direct this until he was forced to bow out following an automobile accident, leaving cameraman Freddie Francis at the helm.
During production, Hammer Productions became the first movie studio to be presented with the Queen's Award for Industry.