Complex sentence: The frigate's name was changed to "Unicorn II" in February 1939, but she was renamed HMS "Cressy" on 20 November 1941, regaining her original name on 14 July 1959 when the carrier was scrapped.
Split into simpler sentences: The frigate's name was changed to "Unicorn II" in February 1939, then to HMS "Cressy" on 20 November 1941. The firgate regained her original name on 14 July 1959, after the carrier was scrapped.