Complex sentence: Her predecessor had been the 74-gun third rate, a former French ship that had been captured at the Battle of Lagos on 19 August 1759 by a fleet under Admiral Edward Boscawen.
Split into simpler sentences: Her predecessor had been the 74-gun third rate. She was a former French ship, and had been captured at the Battle of Lagos on 19 August 1759 by a fleet under Admiral Edward Boscawen.