Naval Battle of Riachuelo The Battle of Riachuelo or simply Battle of Riachuelo , Fought to June 11 of 1865 on the banks of Riachuelo stream , A stream of Paraguay River , province of Corrientes in Argentina . This is regarded by military historians as the most important battles of Paraguayan War ( 1864 - 1870 ) . The forces . Brazilian Empire . The Brazilian forces in the battle of Riachuelo were comprised of a corvette , a steamer and seven gunboats The background . The basin Rio de la Plata was strategic for communications between the Atlantic Ocean and the eastern forts in Andes foothills . The transport of people , animals and goods was done by the rivers , since almost no roads until the second half of twentieth century . The country that controls the navigation of its rivers , but above its mouth , would control the interior of the territory and its economy . Paraguay had no direct outlet to the sea , since the bowl was in the hands of Argentina and Uruguay , the latter in constant dispute between the interests of the Republic of Argentina and Empire of Brazil . For this reason , the most important fortifications of Paraguay had been erected on the banks of the lower course of the river Paraguay . At the beginning of the conflict , the Paraguayan troops had occupied areas of then - province of Mato Grosso ( current state of Mato Grosso do Sul ) in the Empire of Brazil and the Republic of Argentina . If he won the battle of Riachuelo , could navigate freely through the Paraguay River , down the Parana River , conquer Montevideo at Uruguay and , from there , then occupy the province of Rio Grande do Sul . This would be so great Paraguay , because would open the Atlantic for trade with other nations . The Battle of Riachuelo . The Paraguayan fleet left humaita on the night of June 10 , 1865 , headed to the port of Corrientes . López had given specific orders that they should approach stealthly the docked Brazilian steamers before sunrise and board them , thus leaving the ground Brazilian forces bereft of their navy early on during the war . For this , López sent nine steamers , Tacuarí , Ygureí , Marqués de Olinda , Paraguarí , Salto Guairá , Rio Apa , Yporá , Pirabebé and Yberá ; under the command of Captain Meza who was aboard the Tacuarí . However , some two leagues after leaving Humaitá , upon reaching a point known as Nuatá - pytá , the engine of the Yberá broke down . After losing some hours in an attempt to fix it , it was decided to continue with only the remaining 8 steamers . The fleet arrived at Corrientes afer sunrise , however , due to a dense fog , the plan was still executable since most , if not all , Brazilian forces where still on land . However , Captain Meza , not following López ' es orders , ordered that instead of approaching and boarding the docked steamer , the fleet was to continue down the river and fire at the camp and docked vessels as they passed by . This new course of action proved catastrophic . The Paraguayans passed in a line parallel to the Brazilian fleet and continued down the stream . Upon Captain Meza ' s order , the entire fleet opened fire on the docked Brazilian steamers . The land troops hastily , upon realization that they were under attacked , boarded their own ships and began returning fire . One of the Paraguayan steamers was hit in the boiler and one of the " chatas " was damaged as well . Once out of range , they turned upstream and anchored the chatas , forming a line in a very narrow part of the river . This was intended to trap the Brazilian fleet . Admiral Barroso noticed the Paraguayan tactic and turned down the stream to go after the Paraguayans . However , the Paraguayans started to fire from the shore into the lead ship , " Belmonte " . The second ship in the line , " Jequitinhonha " , inadvertently turned upstream and was followed by the whole fleet , thus leaving " Belmonte " alone to receive the full firepower of the Paraguayan fleet — it was soon put out of action . " Jequitinhonha " ran aground after the turn , becoming an easy prey for the Paraguayans . Admiral Barroso , on board of the steamer " Amazonas " , trying to avoid chaos and reorganize the Brazilian fleet , decided to lead the fleet down the stream again and fight the Paraguayans in order to prevent their escape , rather than save " Amazonas " . Four steamers ( " Beberibe " , " Iguatemi " , " Mearim " and " Araguari " ) followed " Amazonas " . The Paraguayan admiral ( Meza ) left his position and attacked the Brazilian line , sending three ships after " Araguari " . " Parnaíba " remained near " Jequitinhonha " and was also attacked by three ships that were trying to board it . The Brazilian line was effectively cut in two . Inside " Parnaíba " a ferocious battle was taking place when the " Marquez de Olinda " joined the attackers . Barroso , at this time heading upstream , decided to turn the tide of the battle with a desperate measure . The first ship that faced " Amazonas " was the " Paraguarí " which was rammed and put out of action . Then he rammed " Marquez de Olinda " and " Salto " , and sank a " chata " . At this point " Paraguari " was already out of action . Therefore , the Paraguayans tried to disengage . " Beberibe " and " Araguari " pursued the Paraguayans , heavily damaging " Tacuary " and the " Pirabebé " , but the nightfall prevented the sinking of these ships . " Jequitinhonha " had to be put afire by " Paraguari " and " Marquez de Olinda " . In the end , the Paraguayans lost four steamers and all of the " chatas " , while the Brazilians only lost the " Jequitinhonha " , coincidentally the ship responsible for the confusion The consequences . The Brazilian fleet left the vicinity of the coast and landed in Corrientes Coast Chaco , To heal the wounded , bury the dead and reorganize . The next morning , the Brazilians weighed anchor and set off downstream toward the south . They were attacked on 12 and 13 June by the batteries of Captain Bruguez . The " Paraguarí " , Who had been hit by the " Amazon " But resisted because it was armored , some months later , Lopez ordered to spend the metal defense " Yporá " And lead to " Paraguarí " Yeyuí River , sinking it here . In order of Lopez , a month after the battle , " Yporá " return to the site of the battle , and protected by the darkness of the night for a possible attack by a Brazilian ship located in the vicinity , came to the remains of " Jequitinhonha " , Stealing one of their guns . Meza was shot in the chest during the battle , and died eight days later in hospital Humaita . Lee , hearing of his death , said : " If he had not died with a bullet , was to die with four , " that is , that should have been shot by the defeat , and ordered that no officer was present at his funeral . Manuel Trujillo , one of the Paraguayan soldiers at the battle , remembered " " When we long for the Brazilian fleet at full steam on the morning of November , we were all surprised because we knew that everything had to do was approach the vapors ' to approach ' " . " He also recalled that during the battle , the ground troops carried the fleet to approach the Brazilian fleet shouted " " Let us go to the vapors ! " We came to steal them , not to be killed by them ! " " . The defeat prevented the Paraguayan column in Paraná River government support to the Uruguay River : the advance of the troops of General Robles stopped at Santa Lucia River , and then ordered him back to Lopez Corrientes . On the other hand , the short - lived conquest of the city and the victory of the Riachuelo up the morale of the Argentine troops , as well as depressed of the Paraguayans and their allies in Corrientes . Besides the overhelming victory for the Brazilians , the battle of Riachuelo got one more victory : they prevented the Paraguayan expansion to the Atlantic Ocean .