Germany’s 1916 pledge to stop sinking merchant ships without warning was called the Sussex Pledge.
Germany issued the pledge to the United States on May 4, 1916, after a German submarine torpedoed the French passenger ferry Sussex without warning on March 24. The attack badly damaged the vessel and killed about 80 people, including the Spanish composer Enrique Granados; several Americans were injured.
Under the pledge, Germany promised that passenger ships would not be targeted and that merchant ships would not be sunk before their military status was established, if necessary through a search. Submarines were also expected to provide for passengers’ and crews’ safety before sinking a vessel.
The pledge temporarily eased tensions between Berlin and Washington, but it did not end the wider submarine-war crisis. Germany abandoned it in January 1917 after deciding that unrestricted submarine warfare might defeat Britain before American intervention mattered. The renewed campaign, alongside the Zimmermann Telegram, helped lead the United States to declare war on Germany on April 6, 1917. The pledge is named after the Sussex, not the Lusitania.