The use of unrestricted submarine warfare was announced by Germany on January 9th, 1917. The use of unrestricted submarine warfare was to have a major impact on World War One as it was one of the main reasons why America joined the war.
When the German Chancellor Bethmann Hollweg announced Germany's intention to use unrestricted submarine warfare, his one major concern and fear was that it would provoke an American response – in this he was to be correct.
