Complex sentence: The ship contracted by the UK Government to observe the radio ships off the Thames Estuary, a former sister ship to Laser 558, the'Gardline Tracker', did not return to continue its watch on Radio Caroline.
Split into simpler sentences: The ship contracted by the UK Government to observe the radio ships off the Thames Estuary. A former sister ship to Laser 558, the'Gardline Tracker', did not return to continue its watch on Radio Caroline.