Battle of Monte Santiago The naval Battle of Monte Santiago was a naval battle on 7 – 8 April 1827 , between the Argentine Navy and Brazilian Imperial Navy , during the Cisplatine War . It was a decisive Brazilian victory , though the Brazilian Navy lost twice as many ships as the Argentine Navy . The battle is highlighted by Argentine historians as one of the most courageous and ferocious naval encounters in the country ' s history . On that day , Sgt . Mayor Francis Drummond ( engaged to Admiral Brown ' s daughter Elisa ) died on deck , firing his marooned ship ' s cannons instead of retreating . The Argentine Navy had severe losses and Brazil gained naval supremacy in the Rio de la Plata . The battle . While the Brazilian Navy had high seas vessels , with more firepower but lesser speed , the Argentine Navy relied on fast maneuvering ships . Some Argentine commanders believed that the lack of maneuvering of the Imperial vessels in shallow waters and the speed of their own ships could decide some engagements in their favor . The Argentine commander was confident that , by using the surprise element , his more maneuverable ships could inflict damage and that he could escape before the Brazilian force could counterattack . Unfortunately for him , he was unaware of the enemy ' s initial three - to - one advantage in terms of ships on the first day of battle ( which escaled into a four - to - one advantage by the second day ) . Brown also underestimated the Brazilian fleet ' s ability to cut off any route of escaping in time . As a result , the battle was a two - day pouring of shells onto his men . On the second day , the Brazilian vessel " Paula " opened fire at the brigantine " Independencia " . The " Independencia " ( which had lesser firepower ) lost its masts , and to prevent the ship from sinking , 12 cannons were thrown overboard . As a consequence Francis Drummond , its captain , was wounded by a sliver that cut his ear . At 4 pm Drummond had no powder left , and had already fired his supply of three thousand rounds . Drummond managed to use anchor chains as amunition . He ordered " abandon ship " , but the crew fiercely refused his command . Then Drummond , in order to resupply amunition , sailed in a lifeboat to the flagship " Republica " . At that moment he was hit by a 24 lb cannonball that destroyed his pelvis and right leg and died . Aftermath . The losses in this battle , along with the loss of the " 25 de Mayo " ( Argentine major vessel ) in the battle of Punta Lara - Quilmes ( June 29 – 30 , 1826 ) , gave the Brazilian Navy control of the River Plate . The Argentine Navy was almost completely destroyed and Brazil achieved naval supremacy . Only raids against commerce could be undertaken by Argentine Navy , mostly from its Atlantic base at Carmen de Patagones , since they could not fight the medium and large ships of the Brazilian Navy . Montevideo and Colonia , the two largest cities in the Banda Oriental , remained under Brazilian control . But the heavy losses sustained by the Brazilians during these battles discouraged them from extending the naval war into the interior rivers of Argentina or attempting a direct attack against Buenos Aires . This situation continued until the Preliminary Peace Convention , by which Oriental Province became the independent nation of Uruguay .