Battle of Juncal The naval Battle of Juncal took place between a squadron of the newly independent United Provinces of the River Plate under command of William Brown and a squadron belonging to the Brazilian Empire , commanded by Sena Pereira . It spanned two days , from the 8th to the 9th of February , 1827 , in the waters of the Rio de la Plata . The two squadrons were initially of roughly equal strength , but because of superior command and control , and artillery training , the Argentines scored a decisive victory : out of 17 Brazilian vessels , 12 — including the flagship with its admiral — were captured and 3 were burnt . Not a single Argentine vessel was lost . In the aftermath of the battle , the Third Division , the arm of the Brazilian fleet tasked with controlling the Uruguay River and thus disrupting communications with the Argentine army then operating in the Banda Oriental , was completely destroyed . The result was the biggest naval victory for Argentina in the Cisplatine War The situation before the battle . The division of the imperial fleet . During the second year of the Argentina - Brazil War , the Brazilians took advantage of their numerical superiority and divided their naval forces operating in the Rio de la Plata sector into three squadrons , or " divisions " . First Argentine advance . To confront the three threats , each of similar or superior strength to his own forces , William Brown acted rapidly to organize a squadron to advance past the mouth of the Uruguay , then find and destroy the Third Division . Typical of Brown ' s audacity , the force he dispatched was in the best case only the equal of the Third Division , while the defense of Buenos Aires was clearly imperiled . The Argentine squadron sailed on the 26th of December 1826 , arriving on the Uruguay River on the 28th . Finding the Third Division , the squadron gave chase , catching it in the Yanguari the next day . Brown sent John Halstead Coe , captain of the " Sarandi " to the Brazilian commander as an emissary to suggest Brazilian surrender . Sena Pereira brusquely responded by taking Coe prisoner and joining the battle , which lasted until the 30th . Due to the lack of wind and the narrowness of the channel , however , maneuver was difficult and the fighting was inconclusive . Impeded from gaining access to the narrow channel , Brown withdrew to the south towards Punta Gorda to wait for the Brazilians . He landed a small force on Vizcaino Island to secure it and send instructions to the militia of Santo Domingo de Soriano to cut supplies to the Brazilian fleet . In response , the Brazilians withdrew further north to Concepción del Uruguay ( then still usually called " Arroyo de la China " ) where they could secure supplies . Worried about the menace that the Mariath Division posed to his rear , Brown decided to fully return to Buenos Aires in search of reinforcements for Martin Garcia Island . He ordered Rosales to return the " Goleta Sarandi " to Uruguay via the Paraná de las Palmas while he finished the preparations , after which he rejoined the fleet by travelling aboard a small whaler . Preparations . On the 6th of January the fortification work was begun . The Mariath Division launched an advance on the island with the corvette " Maceio " and 9 other gunships . On the 18th Brown twice ordered his forces out to meet the Brazilian squadron and both times the Brazilians withdrew after an exchange of cannon fire . Brown wanted on one side to lure the Third Division into combat , yet at the same time he didn ' t want the Mariath Division to join the Third or attack his rear . Helping him navigate the delicate situation was an excellent intelligence network which gave him daily updates on the movement of the Imperial fleet . Essentially , the emissary carrying Rodrigo Pinto Guedes ' orders to Sena Periera had been co - opted by Argentine patriots in Montevideo , and as a result Brown received timely news of the Imperial fleet ' s intentions . Thus , he took notice when Pinto Guerdes communicated to Sena Pereira the orders given to Mariath to advance towards the south . Brown deduced that the Third Division would descend the river on February 7 in order to link up with Mariath . Brown believed that the fortifications and batteries of Martin Garcia would be prepared by then , allowing him to block the Mariath Division while forcing the Third Division into battle . The work at the new fort was duly accelerated ; Brown himself worked as a master mason in the hold of the " Santa Barbara " . On the 5th , the works were ready and in a solemn ceremony Brown named the fort " " Constitución " " . In his speech to the garrison , he informed them that he expected the Argentine squadron to meet Sena Pereira within the next couple days . At the beginning of February there was word that the Third Division was taking on provisions at Arroyo de la China ; by the third it had passed Paysandú and on the 6th it approached Higuerita ( today ' s Nueva Palmira , where it arrived the next day . That same day , Brown outlined his plan and assigning each ship a role in the battle . At 10 that night , the vanguard of the Argentine fleet reached the mouth of the Paraná Guazú River and waited for the rest of the fleet to arrive . The battle . Combatants . Argentina ( Brown ) . 15 vessels , 73 guns , approximately 750 men Brazil ( Pereira ) . 17 vessels , about 750 men The Argentine squadron numbered 15 vessels , including three major ships : the flagship " Goleta Sarandí " under the direct command of Brown , the " Goleta Maldonado " under the command of the young Francisco Drummond — fiance of Brown ' s daughter — and the Bergantín Balcarce , with 14 cannons and under the command of Francisco José Seguí . Rounding out the squadron were the schooners " La Pepa " , under Calixto Silva , " Guanaco " ( Guillermo Enrique Granville ) , " Unión " ( Shannon Malcolm ) , the smack " Uruguay " ( Guillermo Mason ) , and 8 gunboats . In total , 69 cannons and a crew of approximately 750 men . The Brazilian squadron included 17 vessels : the flagship " Goleta Oriental " under command of Jacinto Roque de Sena Pereira , the " Bergantín Dona Januária " under Pedro Antonio Carvalho , the " Goleta Bertioga " under Lieutenant George Broom , the " Liberdade do Sul " under Lieutenant Augusto Venceslau da Silva Lisboa , the " 12 de Outubro " , the " Goleta Fortuna " ( a hospital ship ) , the " Goleta Vitoria de Colonia " , the " Goleta Itapoã " under the command of lieutenant Germano Máximo de Souza Aranha , the " Goleta 7 de Março " , the " Goleta Brocoió " under Francisco de Paula Osório , the " Goleta 9 de Janeiro " , the " Goleta 7 de Setembro " , two gun schooners ( the " Atrevida " and the " Paraty " ) and the " cañoneras " " Cananéia " , " Paranaguá " , and " Iguapé " . In total , 65 guns and approximately 750 men . For the first and only time during the war , there was relative parity between the forces , or at least , the Brazilian advantage was not so great . Approach of the fleets . The Argentine squadron spent the night of February 7 anchored between Juncal Island and the west bank of the river . At dawn on the 8th the sails of the Brazilians were spotted descending the river , taking advantage of a gentle north wind . Brown gave the order to weigh anchors and place his ships in a line of battle arrayed obliquely to the southeast from Juncal Island . The " goleta " " Sarandi " formed the center of the line , with " Maldonando " in the vanguard and " Balcarce " in the rear . The Brazilian fleet continued its advance until the wind died down around 11 : 30 , at which point it anchored some 1 , 000 yards from the Argentine line , with the flagship " Oriental " in the center . Beginning of the battle . The weather on the 8th was stormy , hot and humid , with light and variable winds ; typical for that time of year in the litoral regions . Sena Pereira anchored his ships and unleashed a fire ship toward the enemy fleet . However , this was promptly sunk by Argentine gunfire . At noon Brown ordered forward a detachment of 6 of his gunboats , which could fire at a longer range than his other vessels with their 18 pounder guns . However the Argentine long guns had longer range and were manned by superior gunners . After exchanging fire for approximately two hours , a sudden " sudestada " ( Sudestada ( Southeast blow ) is the Spanish name for a climatic phenomenon common to the Río de la Plata ) separated the fleets and forced them to suspend the battle . The Brazilians maintained the dominant , windward position ; because the wind was blowing towards the Argentines , the Brazilians had the initiative . Sena Pereira duly tried to stage his ships in an attack line . However , the maneuvers of the vessels was disastrous : the goleta " Liberdade do Sul " grounded , while the " Dona Januária " left the formation and strayed within range of the fire of " General Balcarce " , the " Sarandí " , and 3 gunboats . At 3 in the afternoon the wind again died down , and the action was again reduced to a long range artillery duel . Visibility was steadily reduced by the smoke of the guns , which were audible as far away as Buenos Aires and Colonia del Sacramento . Once again a severe storm rolled in and the fleets struggled fruitlessly to maintain their positions . The " General Balcarce " began to settle , but succeeded in remaining afloat . Eventually the storm died down and was replaced by a northeast breeze . Sena Pereira attempted to take advantage of the new wind by retiring to the north to take up better positions . Once again , the resulting maneuver was poor . The " 12 de Outubro " could only be saved by the help of the remaining ships , while the hospital ship " Fortuna " was unable to anchor and was blown towards the Argentine lines , where she was captured . As a result of the " Fortuna ' s " capture John Halstead Coe ( comodoro Juan Coe ) was freed after having been a prisoner on board since December 1826 . It was midnight before the Brazilian squadron was fully reunited in a disorderly anchorage near Sola Island . Second day . Exhausted , the Brazilians were not able to lay any plans that night . At dawn , the captains of the fleet boarded the " Oriental " to decided the plan of battle ; basically , to choose between fighting while maneuvering or to remain anchored . Sena Pereira did not make a decision and opted to choose his tactics as the situation developed . For his part , Brown was ready . At 8 am , with a southeast breeze , he ordered the " Sarandí " to run up a red flag , the signal for the Argentines to occupy the windward position , marshal into a battle line , and advance towards the Brazilians . In response , Sena Pereira gave the order to form a battle line and drop anchor . However , once again , the result was confusion and disorder : some of the gunboat drifted out of formation and downwind . Sena Pereira , shouting ineffectively with a megaphone , tried to restore order . With the Argentines closing quickly and in good order , he changed his decision , now ordering his fleet to raise anchors and attempt to maneuver . The " Dona Januária " , the " Bertioga " and the " Oriental " duly advanced on the approaching Argentines , but without the support of the rest of the squadron , which remained dispersed behind them . The three ships were quickly engaged by the " General Balcarce " and the Argentine vanguard . The Argentine fire was effective : a shot from the " General Balcarce " soon destroyed the " Januária " ' s bowsprit , and another knocked down her foremast , causing such disruption that she was on the point of foundering . Sena Pereira ordered the small schooner " Vitoria de Colonia " to take " Januária " under tow , but the schooner " Uruguay " blocked the way . The attack was so rapid and devastating that the captain of the " Januária " , Lieutenant Pedro Antonio Carvalho , ordered his cannons to concentrate on the Argentine artillery while a team remained to attempt to scuttle the ship and he departed with the crew in boats towards the east . For his part , Drummond , commander of the " Maldonado " , attacked the " Bertioga " , under the command of his old comrade , Lieutenant George Broom . An accurate shot from a heavy Argentine gun knocked down the main mast of the " Bertioga " and the ship , now unable to maneuver , was forced to surrender after a half hour of combat . Throughout this time , the " General Balcarce " under Francisco Seguí led a combined attack against the " Oriental " . The intense crossing fire knocked out the " Oriental " ' s cannons , half of its carronades , and caused 37 casualties , including Sena Pereira . Despite the losses the Brazilians refused to strike their colors , which had been nailed to the mast . Finally the ship was boarded and Seguí accepted the sword of the Brazilian commander as a sign of surrender . With the surrender of the " Oriental " , the remaining vessels of the Brazilian fleet disengaged and attempted to flee , turning the Argentine victory into a rout . Brown transferred his flag to the " General Balcarce " and ordered the " Sarandí " and the gunboats to give chase to the broken Brazilian squadron . He boarded the surrendered Brazilian flagship and was presented with the sword of the Brazilian commander , at which he commended Francisco Seguí with the words " " Usted es el héroe " " ( " You are the hero " ) . Brown retired with four of the prizes towards Martín García to repair damages , write his report , and prepare for the eventual attempt of the Mariath Division , stationed to the south of the island , to force its way north . Martín García . Mariath ' s orders were to use his 10 vessels to overcome the fortifications at Martín García , attack the Argentine rear , and reinforce the Third Division . Although he could already hear cannon fire in the distance , Mariath moved slowly and with great caution . As the main Argentine battery ( consisting of 9 24 pounders ) were on the west side , covering the Grand Canal , Mariath sent a schooner down the Canal del Infierno , the passage to the east of the island , in order to determine if the water was deep enough for his squadron . In response , the garrison moved its mobile battery ( consisting of 2 12 pounders and a Congreve rocket launcher ) to the east to defend against a possible landing . The move proved unnecessary , however , as the Brazilian vessel ran hard aground . Mariath was thus dissuaded from taking the eastern route , although his pilot thought it still possible . He commenced an artillery duel with the main batteries , until the storm obliged him to suspend the indecisive action . At this point , Mariath believed that the shallow water , the unpredictable weather , and the formidable batteries at Martín García made passing the island too risky . Thus , on the 9th , while the Third Division was being destroyed , the Mariath Division remained in the distance as a spectator . On the 10th , Mariath finally decided to withdraw in the direction of Colonia de Sacramento , where he arrived a week later . The first news of the defeat reached the Brazilians on the morning of February 12 , when 8 survivors of the " Oriental " arrived . Their stories were confirmed by the boat of Lieutenant Carvalho , and later , on the 14th , by the arrival of the only survivors , the schooner " Vitoria de Colonia " and a gunboat , escorted by the frigate " Dona Paula " . The chase . On the day following the battle , the schooner " Brocoio " was pursued and captured , in addition to two gunboats ( the " Paraty " and the " Iguape " ) that ran aground in the mouth of the Paraná River and were likewise made Argentine prizes . At this point the Third Division was reduced to the schooners " Liberdade do Sul " , " Itapoã " , " 7 de Março " , " 9 de Janeiro " and " 7 de Setembro " , the gunboats " Cananéia " y " Paranaguá " , and an assortment of smaller launches . All of these surviving and functioning vessels were in full flight north up the Uruguay River . The German skipper of the schooner " Itapoã " , a Lieutenant Souza Aranha , took command of the reduced squadron , which soon suffered further setbacks : the schooners " Liberdade do Sul " , the " Itapoã " and the " 7 de Março " all ran aground and were burnt to prevent capture . The dwindling fleet continued north with a total of 351 officers and crew piled aboard , with the intent of surrendering to the authorities of the Province of Entre Ríos . Rapidly completing the reorganization of his forces , and in face of the withdrawal of the Mariath Division , Brown quickly returned his attention to the survivors of Juncal . Already on the 14th he had returned to the Uruguay River in the " Maldonado " , accompanied by some 6 other vessels . On the 15th he arrived at Fray Bentos and received the news that Souza Aranha , after casting his cannons into the sea , had surrendered his ships to the governor of Entre Ríos . Brown anchored outside Gualeguaychú and asked for the handover of the ships and prisoners . However , the Entre Ríos authorities resisted these demands , foreseeing that such a capitulation would have grave results for their own cherished autonomy . In response to this rebuff Brown mounted a successful combined land and sea operation which resulted in the final capture of the Brazilian fleet . Aftermath . With 12 vessels captured , three burnt , and only two survivors , the battle imposed a significant loss on the Brazilians and represented the greatest triumph of the Argentine fleet . In the larger scope of the war , the victory frustrated the Brazilian attempt to cut the lines of communication to the expeditionary force . In addition , it denied the Brazilians use of the Uruguay River to stage an offensive against the Argentine litoral , an offensive which at a minimum could have detached the litoral provinces from the Confederation and at worst may have threatened its existence . In Buenos Aires , Brown was received with bonfires and orchestras . He was elevated to most popular figure of the Republic . Sena Pereira remained a prisoner of Brown , who recognized his valor and commended him to the Argentine government " for his brave and intrepid defense , performed by a soldier " . However , Pereira refused to give any pledge and eventually escaped . At the beginning of 1829 , he would be one of those who handed over the plaza of Montevideo to the westerners . The republican naval victory off Juncal was rapidly followed on land by Ituzaingó ( 20 Feb ) and Carmen de Patagones ( 28 Feb ) . After this , the conflict ground to a halt , as the Brazilian Empire had been defeated in various fronts while Argentina was incapable of taking advantage of the situation given that the Naval blockade still persisted , especially after the Battle of Monte Santiago which almost fully destroyed the Navy of the United Provinces of the Rio de la Plata , and also given that Montevideo and Colonia , the two largest cities in the Banda Oriental , were still under control by the Empire of Brazil . This situation would continue until the Preliminary Peace Convention , by which Oriental Province became the independent Western State of Uruguay .