RMS Leinster (2,640 gross tons) was built in 1897 at Laird Brothers, Birkenhead for the City of Dublin Steam Packet Company. At the time she was one of the fastest ships at sea with a speed of 24 knots. She operated between Holyhead and Kingstown (now Dun Laoghaire).
Shortly before 9.00 am on 10 October 1918 the RMS Leinster left Carlisle Pier, Kingstown, bound for Holyhead carrying 697passengers, 76 crew and 22 postal sorters from Dublin Post Office under the command of Captain William Birch. Of the passengers there were more than 180 civilians and 495 military personnel, going on, or returning, from leave.
Just before 10.00 am, having travelled about sixteen miles, a torpedo fired from the German submarine UB-123 struck the port side where the postal sorting room was located, causing an explosion, before ripping out through the starboard side. In an attempt to return to port, the listing Leinster turned back to Kingstown, and by this time lifeboats were being launched. Another torpedo struck the ship on the starboard side, causing massive destruction, with the ship sinking shortly afterwards. Officially, 501 people died in the tragedy. However, recent research has traced the names of 547 casualties.
Details of crewmembers from Holyhead lost on the Leinster can be found here - Holyhead War Memorial