The screenplay is based on a novel by Anthony Dawson, the British character actor probably best known for playing Professor Dent in 'Dr. No'.
Director Guy Green later said that before the shooting, Peter Van Eyck did not know how to swim and no one ever told him he would have to learn.
When the characters speak Italian, the subtitles have a consistent error. When the character says "Signora (Mrs.)" the subtitle always has "Señora" which is Spanish not Italian. Similarly "Signor (Mr.)" is always shown as "Señor" and "Signorina (Miss)" becomes "Señorita".
Opening credits: All characters and incidents portrayed and the names used, are fictitious.