After the humiliating defeat at the Battle of Papudo and the indecisive Battle of Abtao, Rear Admiral Casto Méndez Núñez was ordered to take punitive action against South American ports. When the Chilean government ordered that vessels supplying or communicating with the Spanish fleet should not be allowed to enter Chilean ports, Méndez Núñez's first target became the most important and undefended Chilean city of Valparaíso.