The RMS Lusitania was a British-registered ocean liner that was torpedoed by an Imperial German Navy U-boat during the First World War on 7 May 1915, about 11 nautical miles off the Old Head of Kinsale, Ireland. The attack took place in the declared maritime war-zone around the UK, three months after unrestricted submarine warfare against the ships of the United Kingdom had been announced by Germany following the Allied powers' implementation of a naval blockade against it and the other Central Powers.

RMS Lusitania was an ocean liner launched by the Cunard Line in 1906. She was the world's largest passenger ship until the completion of the Mauretania three months later and was awarded the Blue Riband appellation for the fastest Atlantic crossing in 1908. The Lusitania was sunk on her 202nd trans-Atlantic crossing, on 7 May 1915 by a German U-boat 11 miles (18 km) off the Old Head of Kinsale, Ireland, killing 1,197 passengers, crew and stowaways. The sinking occurred about two years before the United States declaration of war on Germany but significantly increased public support in the US for entering the war.