The British transatlantic liner, Lusitania, was sunk by a German U-boat on May 7th 1915.
Almost 1,200 people died when the ship was torpedoed off the Irish coast while on a crossing from New York to Liverpool.
More than 100 of the victims were Americans, provoking a diplomatic row between the neutral United States and Germany.
The Germans had given a warning that all merchant ships in the seas around Britain and Ireland risked attack without warning.
The move was in retaliation for the Allied naval blockade imposed at the start of the First World War, and the British declaration of the North Sea as a war zone in November 1914.
The Lusitania’s cargo included quantities of ammunition.