Complex sentence: The Cork route was operated by "Tregastel" and "Quiberon", later to be joined by "Celtic Pride", operated by Swansea Cork Ferries, supplying a midweek Cork-Roscoff round trip.
Split into simpler sentences: The Cork route was operated by "Tregastel" and "Quiberon". They would later be joined by "Celtic Pride" operated by Swansea Cork Ferries who supplied a midweek Cork-Roscoff round trip.