Complex sentence: The French conceived a plan by which a squadron from Brest, under rear Admiral Willaumez, would sail to Lorient, engage the blockading ships and distract them while Troude's squadron would set sail and make its junction with Willaumez' forces.
Split into simpler sentences: The French conceived a plan by which a squadron from Brest, under rear Admiral Willaumez, would sail to Lorient. It would then engage the blockading ships and distract them while Troude's squadron would set sail and make its junction with Willaumez' forces.