In April 1975 Sealink closed the Heysham - Belfast car ferry service operated by the sisters Duke of Lancaster and Duke of Argyll. An effort to maintain the link between the two ports was made a few months later when, in a joint venture with the Belfast Steamship Co (P&O) the Ro-Ro ferry Penda was introduced. Joining the Penda in 1978 was the former Stranraer vessel Dalriada.



In January 1980, in an effort to boost the struggling service, the Penda and the Dalriada were both replaced by two larger and newly chartered Ro-Ro ferries; the Lagan Bridge and the Lune Bridge. Each ship operated six nights a week, offering sailings in each direction. Regular weekend sailings on the Holyhead - Dun Laoghaire service were also offered between their scheduled Heysham crossings.