Complex sentence: The ship, and her sister HMS "St. David" (originally "Suffolk Conquest") were returned to their original owner in November 1983 and reverted to their former names and converted into oil rig safety/standby vessels.
Split into simpler sentences: The ship, and her sister HMS "St. David" (originally "Suffolk Conquest") were returned to their original owner in November 1983. They reverted to their former names and were converted into oil rig safety/standby vessels.