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.

Royal Mail Ship, usually seen in its abbreviated form RMS, is the ship prefix used for seagoing vessels that carry mail under contract to the British Royal Mail. The designation dates back to 1840. Any vessel designated as "RMS" has the right both to fly the pennant of the Royal Mail when sailing and to include the Royal Mail "crown" insignia with any identifying device and/or design for the ship.