"The seas' ruler, he gazed southward over the bay, empty save for the smokeplume of the mailboat vague on the bright skyline and a sail tacking by the Muglins." (U1.575)
This PC shows RMS (= Royal Mail Service) Leinster, one of the mailboats in service on the Irish Sea in 1904. The others were RMS Munster, Ulster, and Connaught. They carried the mail from Kingstown to Holyhead (Wales), from whence it was distributed by train to its various destinations. The mailboats also took passengers. RMS Leinster was built and started service in 1897; she was sunk by a German U-boat on her way to Holyhead in 1918.