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 8 to 9 February 1827, in the waters of the Río de la Plata.
The two squadrons were initially of roughly equal strength, but because of superior command and control, and gunnery 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 Cisplatina province, was completely destroyed. The result was the biggest naval victory for Argentina in the Cisplatine War.

The situation before the battle

The divisions of the imperial fleet

During the second year of the Cisplatine War, the Brazilians took advantage of their numerical superiority on sea and divided their naval forces operating in the Río de la Plata sector into three squadrons, or "divisions".

The first division, "Bloqueio", was placed under the command of John Charles Pritz. It was tasked with blockading traffic to and from the port of Buenos Aires and secondary departure points such as Las Conchas, Ensenada de Barragán, and the mouth of the Salado River;
The second division, named "Oriental" or "Mariath", was tasked with securing the Uruguayan coast from the mouth of the Uruguay River to the Río de la Plata. The bulk of this division was put under the command of Frederico Mariath, who would later support the Third Division;
The "Third Division", under the command of Jacinto Roque de Sena Pereira, was to remain in the Uruguay River in order to divide the Argentine front and exploit political fault lines between the province of Entre Ríos and Buenos Aires that had been exacerbated by the passing of the Unitary Constitution of 1826. By controlling the Uruguay River, the supply lines to an Argentine expeditionary force in the contested territory of Cisplatina would be cut, and the Brazilians would have freedom of maneuver for a later attack on the Argentine flank.
First Argentine advance

To confront the three threats, each of similar or superior strength to his own forces, the Argentine commander, William Brown, acted rapidly to organize a squadron to advance past the mouth of the Uruguay River, then find and destroy the Third Division.
Simultaneously, to stop reinforcements from arriving from the Mariath Division and to secure his rear, he moved to fortify the island of Martin Garcia while he left the defense of the Buenos Aires coast to his flagship, the brig Independencia, along with the brig Republica, the barque Congreso, and four gunboats under the command of Leonardo Rosales.
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 26 December 1826, arriving on the Uruguay River on 28 December. After finding the Third Division, the squadron chased it, catching it in the Yanguari the next day. Brown sent John Halstead Coe, captain of Sarandí to the Brazilian commander as an emissary to request the Brazilians to surrender. Sena Pereira responded by taking Coe prisoner and joining the battle, which lasted until 30 December. However, due to the lack of wind and the narrowness of the channel maneuvering was difficult and the fighting was inconclusive.
Unable from gaining access to the narrow channel, Brown withdrew to the south towards Punta Gorda to await the Brazilians. He landed a small force on the Vizcaino Island to secure it and sent 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 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 Sarandí 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 6 January the fortification work was begun. The Mariath Division launched an advance on the island with the corvette Maceió and nine other gunships. On 18 January 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 did not 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 Pereira 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 Guedes informed Sena Pereira of the orders given to Frederico Mariath to advance towards the south. Brown deduced that the Third Division would descend the river on 7 February in order to link up with Mariath. Brown believed that the fortifications and batteries of Martin Garcia would be ready 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 Santa Barbara. On 5 February, 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 6 February it approached Higuerita where it arrived the next day. That same day, Brown outlined his plan and assigned each ship a role in the battle. At 10 pm, 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

Sarandi 7
Balcarce 23
Maldonado 8
Pepa 2
Guanaco 8
Union 10
Uruguay 7
8 1-gun launches
Brazil (Pereira)

17 vessels, about 750 men

Oriental 11 - Captured
Januaria 14 - Captured
Bertioga 8 - Captured
4 2-gun schooners - Captured
4 2-gun gunboats - Captured
? - Captured
3 vessels - Burnt
2 others

The Argentine squadron numbered 15 vessels, including three major ships: the flagship goleta under the direct command of Brown, the goleta Maldonado under the command of the young Francisco Drummond—fiance of Brown's daughter—and Bergantín Balcarce, with 14 cannon and under the command of Francisco José Seguí. Rounding out the squadron were the schooners La Pepa, under Calixto Silva, Guanaco, Unión, the smack Uruguay, and eight gunboats. In total, 69 cannon and a crew of approximately 750 men.
The Brazilian squadron included 17 vessels: the flagship goleta Oriental under the command of Jacinto Roque de Sena Pereira, Bergantín Dona Januária under Pedro Antonio Carvalho, the goleta Bertioga under Lieutenant George Broom, Liberdade do Sul under Lieutenant Augusto Venceslau da Silva Lisboa, 12 de Outubro, the goleta Fortuna, 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 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 7 February anchored between Juncal Island and the west bank of the river. At dawn on 8 February the sails of the Brazilians were spotted descending the river, taking advantage of a gentle north wind. Brown gave the order to weigh anchor and placed 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 am, at which point it anchored some from the Argentine line, with the flagship Oriental'' in the center.

Beginning of the battle

The weather on 8 February 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 six of his gunboats, which could fire at a longer range than his other vessels with their 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 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 were disastrous: the goleta Liberdade do Sul grounded, while Dona Januária left the formation and strayed within range of the fire of General Balcarce, Sarandí, and three gunboats.
At 3:00 pm 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. 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. 12 de Outubro could only be saved with 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 Fortunas capture John Halstead 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.