RMS Leinster

RMS Leinster was an Irish ship operated by the City of Dublin Steam Packet Company. She served as the Kingstown-Holyhead mailboat until she was torpedoed and sunk by the German submarine on 10 October 1918, while bound for Holyhead. She sank just outside Dublin Bay at a point 4 nmi east of the Kish light.

The exact number of dead is unknown but researchers from the National Maritime Museum of Ireland believe it was at least 564, which would make it the largest single loss of life in the Irish Sea.