Complex sentence: The fleet managed to chase the Portuguese from Muscat, modern Aden, in August 1552 in the Capture of Muscat, but what unsuccessful in the Siege of Hormuz in September of the same year.
Split into simpler sentences: The fleet managed to chase the Portuguese from Muscat, modern Aden, in August 1552 in the Capture of Muscat. However, they were unsuccessful in the Siege of Hormuz in September of the same year.