Battle of the Saltes Island The naval Battle of the Saltes Island or Battle of Saltes ( " Spanish : Batalla de la Isla Saltés " ) took place on 17 July 1381 , off Saltes Island , between the Kingdom of Castile and the Kingdom of Portugal during the Third Ferdinand War . The Castilian fleet commanded by Don Fernando Sánchez de Tovar defeated decisively the Portuguese fleet led by João Afonso Teles de Menezes , Count of Barcelos . The result of the battle was the destruction of the naval offensive capability of Portugal , achieving the Castilian naval supremacy in the Atlantic Ocean . Background . Ferdinand I of Portugal , following the death of Peter I of Castile , declared war on Kingdom of Castile for the possession of the Castilian throne . This series of conflicts were known as Ferdinand Wars . In 1381 , breaking the Treaty of Santarem ( 1373 ) , which brought peace to the second war , Ferdinand I decided to attack back to Castile , thus initiating the Third Ferdinand War . For this , he signed an alliance with the young Richard II of England . John of Gaunt , Duke of Lancaster , also had , since 1371 , claims to the Castilian throne , and saw in this deal a means of enforcement of this cause , and sent about 2 , 000 English soldiers under the command of the Earl of Cambridge to Lisbon , to support a Portuguese incursion into the Castilian territory . To prevent the English contingent being intercepted at sea by the navy of Castile , the Portuguese monarch planned a naval blockade . In mid - July 1381 , from Lisbon , a Portuguese fleet under the command of João Afonso Teles de Menezes , Count of Barcelos , sailed towards the mouth of the Guadalquivir river to prevent the passage of the Castilian fleet , which was anchored in Seville . At the same time , Admiral Fernando Sánchez de Tovar sailed from its base in Seville , heading out to the Portuguese coasts . On 17 July , sailing in opposite directions , the two fleets were sighted each other off the Algarve . At that time , after assessing the situation , the Castilian Admiral considered very unlikely to obtain a victory under such circumstances , and ordered to tack and return to port . His Portuguese counterpart then saw a unique opportunity to beat the rival , and began the chase of the Castilian fleet . From that moment it became clear the tactical intelligence of the Admiral De Tovar as sailor , and ordered to his men rowing at a fast pace , forcing his Portuguese pursuers maximize the effort to try to overcome the speed of the opponent , and the different speeds at which they advanced , would increase the distance between the Portuguese ships , breaking their formation . After about two hours , the exhaustion , the thirst and the heat of summer took their toll on the Portuguese rowers , and many of their ships were left behind . Eight of them , the vanguard of the Portuguese fleet , attacked the small island of Saltés and destroyed the property of the fishermen in the vicinity . Then , De Tovar , seeing that the Portuguese had fallen into his trap , launched their ships against the enemy in a compact formation , and captured easily the Portuguese galleys . The rest of the Portuguese fleet , approached in disarray one by one , and were captured by the Castilians without difficulty . Eventually , only one of the 23 Portuguese galleys , avoided being captured by the men of Fernando Sánchez de Tovar . The Castilian fleet obtained a brilliant victory . Consequences . Admiral Fernando Sánchez de Tovar entered triumphantly with his 22 galley s captured in the port of Seville , with great joy of its inhabitants . This fact allowed the English to dock in Lisbon without problems . Later , the English men of the Duke of Lancaster , arranged their boats to face off against the fleet of Sánchez de Tovar , but knowing that he had returned to Seville , the English ships returned to England , leaving in Lisbon to the English land forces . The resounding victory of Don Fernando Sánchez de Tovar had obvious implications for the Third Ferdinand War . Annulled the naval offensive capability of Portugal , achieving the Castilian naval supremacy in the Atlantic Ocean . That year , the Portuguese could not build more fleets against Castile , who , in turn , did not need to do the same , and the Castilians exercised an effective control of the sea . Therefore , the battle ended the naval Portuguese campaign of 1381 . The effects of the Portuguese defeat also felt in the following year , when the Kingdom of Portugal had to face , militarily weaker than usual , a vigorous attack by sea and land from the Crown of Castile . The Castilians came to the gates of Lisbon , forcing the King of Portugal to sign peace in August with John I of Castile , by the Treaty of Elvas .