On 4 October 1918, only six days before RMS Leinster was sunk, U-boat UB-91 attacked and sank the Japanese merchant ship, Hiranu Maru, 200 miles south of Ireland. There were only 29 survivors from 320 on board. Japan at that time was an ally of Britain and the ship was therefore considered a legitimate target. This tragedy demonstrates how dangerous the seas were in the western approaches to Britain and along the Irish Sea during this stage of the war.
Previously, in January 1918, the Hiranu Maru was in collision with the British ship SS Hildena about 4 miles north of the Skerries, Anglesey. It happened at night when the vessel was travelling in a convoy without lights. SS Hildena floundered with the loss of all hands. Among the crew was 2nd Engineer, Robert Jones of Holyhead.