The B&CDR had owned and run steamships since 1893, mainly between
Belfast and
Bangor but also to other destinations in
County Down and
County Antrim. At the end of the 1911 summer season the railway planned to sell , which dated from 1894, and replace her with a new, larger and more modern ship. The company ordered ''Erin's Isle
from A&J Inglis of Pointhouse, Glasgow, who launched her on 12 June 1912 and fitted her out in less than a month. The B&CDR named her after "Erin", the Hiberno-English version of the Irish Éirinn'', meaning Ireland. ''Erin's Isle'' entered B&CDR service on 12 July 1912. She worked seasonally from mid-May to the end of September each year, making regular scheduled runs between Belfast and Bangor and between Bangor and
Larne, plus excursions from Bangor to other destinations. She ended her fourth summer season on 29 September 1915. ==With the Royal Navy==