The "Dulcibella" sailing yacht seen in the movie weighed seven tons and spanned 30 feet. The boat was discovered in Cornwall and converted for the film's sailing sequences. The yacht was actually built in the same shipyard as the vessel "Vixen" which was a boat owned by original source author Erskine Childers whose experiences aboard her inspired the film's "Riddle of the Sands" source novel.
The author of the novel, Erskine Childers, was a British Army veteran of the Boer War and World War I. He became an Irish nationalist and revolutionary leader. He was later executed during the Irish Civil War on November 24, 1922. His son Erskine Hamilton Childers served as the fourth President of Ireland from June 25, 1973 until his death on November 17, 1974.
To prepare for the sailing sequences in this picture, actors Jenny Agutter and Simon MacCorkindale went on a crash sailing course at Cowes prior to principal photography.
Kaiser Wilhelm II is never depicting using his left hand in the film. Wilhelm's left arm was withered from birth; he was very self-conscious about it and kept it hidden whenever possible.
This 1979 British film was not released in the USA until 1984, five years after it had premiered in the UK.