In "The Dark Side of Genius", Donald Spoto wrote that Tallulah Bankhead would climb a ladder every day to reach the tank where the filming took place. She never wore underwear and regularly received an ovation from the film crew.
During filming, several crew members noted that Tallulah Bankhead was not wearing underwear. When advised of this situation, Alfred Hitchcock observed, "I don't know if this is a matter for the costume department, makeup, or hairdressing."
The harsh conditions of the shoot took its toll: actors were soaked with water and oil, which led to two cases of pneumonia for Tallulah Bankhead, an illness for actress Mary Anderson and two cracked ribs for actor Hume Cronyn, according to his autobiography. Production was temporarily halted twice to allow for recovery of the cast.
Seasickness hit the entire cast at various times during production, and many of them caught pneumonia after constant exposure to cold water, Tallulah Bankhead having suffered twice from it. Hume Cronyn almost drowned in a storm scene when he got caught under a large metal water-activator, used for making waves. Joe Peterson, a lifeguard hired especially for the production, saved him in the nick of time. Cronyn also suffered from cracked ribs during the course of filming.
Tallulah Bankhead was cast in the film because Alfred Hitchcock wanted to use "the most oblique, incongruous person imaginable in such a situation". She was Hitchcock's first choice for the role of Constance 'Connie' Porter.
For the German-dubbed version the challenge was to maintain the tension between the English-speaking majority in the boat vs. Willy and Connie Porter talking German. This problem was "solved" having Willy pretend to be a Dutch volunteer with the Kriegsmarine and shifting the Willy-Porter conversation to the Dutch language.
The film was shot entirely on a restricted set in which the boat was secured in a large studio tank. Alfred Hitchcock, always striving for realism, insisted that the boat never remain stationary and that there always be an added touch of ocean mist and fog compounded of oil forced through dry ice.
Screenwriter John Steinbeck, a noted liberal, was outraged by what he regarded as director Alfred Hitchcock's racism as manifested in his condescension towards the George 'Joe' Spencer character played by Canada Lee.
in "before" and "after" pictures in a newspaper advertisement for Reduco Obesity Slayer. The pictures were genuine, as he had just been on a crash diet (although not with the fictional Reduco) from 300 to 200 lbs. However, the so-called "Reduco Obesity Slayer" diet pill or potion ad seemed so real that people who had seen the film called the studio and wrote letters to Hitchcock asking where could they get this product. (In Rope (1948), a neon sign advertising "Reduco" with Hitchcock's famous silhouette is seen outside the Manhattan apartment where the film takes place.)