 The film was shot mainly aboard a real ocean liner. The Hamburg had  recently been sold by its German owners to the Soviet Union. Before  the Soviets took delivery of the liner, they rented it to the film  company. The liner was painted in the livery of a fictional shipping  line, very similar to the livery used by the Soviet Morpasflot line,  and renamed the Britannic. Advertisements were run in British  papers, soliciting extras who would take a lengthy cruise in the  North Sea for free, but with the knowledge that the ship would  actually seek out the worst possible weather, as the story demanded  seas too rough for the lifeboats to be lowered, trapping the  passengers on board.