Complex sentence: When "Guerrière" spotted two other frigates which did not appear to answer her signals correctly, she erroneously believed them to be part of the American squadron, and veered away but the two frigates were in fact "Belvidera" and "Aeolus".
Split into simpler sentences: When "Guerrière" spotted two other frigates which did not appear to answer her signals correctly, she erroneously believed them to be part of the American squadron, and veered away. The two frigates were in fact "Belvidera" and "Aeolus".