| Conflict: | Assault on Barroso and Rio Grande |
| Partof: | the Paraguayan War |
| Place: | Tagy, left bank of the Paraguay River |
| Result: | Brazilian victory |
| Combatant1: |  Paraguay |
| Commander2: |
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| Strength1: | 20 canoes
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| Strength2: | 2 ironclads: |
| Casualties1: | 74: 42 killed 32 captured |
| Casualties2: | 11: 3 killed 8 wounded |
The assault on the battleship Barroso and the monitor Rio Grande, also known as assault on the battleships at Tagy, was a Paraguayan naval operation carried out during the Paraguayan War. The Imperial Brazilian Navy was present in the main actions of the allied forces. President Francisco Solano López knew of the threat that the navy posed and wanted to capture some of its ships, the ironclads. The seizure was also seen as a form of compensation for the losses incurred as a result of the war. Assault plans were created and executed in 1868.
On 9 July 1868, at 11:50 pm, 270 Paraguayan soldiers, known as, attacked two Brazilian battleships, Barroso and Rio Grande, anchored near the Tagy ravine, located on the left bank of the Paraguay River. The approach attempt was not simultaneous, which allowed each vessel to support itself with their respective artillery pieces. Imperial Brazilian Army infantry encamped near Tagy also supported the ships. Despite being well armed and having managed to climb to the deck of both vessels, the bogavantes were not successful, being quickly repelled. The Paraguayans suffered 74 casualties and the Brazilians 11.
After the defeat of the bogavantes, the last forces that protected the fortress of Humaitá and that depended on their victory abandoned the stronghold and tried to flee to the Chaco, however they were surrounded and defeated by Brazilian troops. The fortress was occupied shortly thereafter.
The defeat of the Paraguayan navy in the Naval Battle of Riachuelo, on 11 June 1865, forced Solano López's forces to retreat to their own territory. Then, the allied invasion of Paraguay began with the Battle of Paso de Patria in 1866, when the allies landed in the country. The tactic employed by the invading forces was the use of the Imperial Navy as a support force for the troops on land, transporting men, supplies and fighting the various fortifications and vessels along the Paraguay River and its tributaries. However, the allied defeat at the on 22 September 1866 halted their operations for at least a year until allied naval forces broke through the fort on 15 August 1867, supported by land troops who also carried out the capture of the Tagy ravine, located on the left bank of the river and above the fortress of Humaitá, another stronghold to be overcome. With the conquest of Curupayty and Tagy, the allies were able to coordinate logistics that supported the battleships stationed below Humaitá so that they could also force their transposition. It was not until 19 February 1868 that six Brazilian ironclads successfully transposed Humaitá.
After the passage, Humaitá became unreachable by the river, which forced the Paraguayans to build a road in the Chaco that linked the fortress to the so that supplies were not cut. However, the constant bombardment by Brazilian ironclads and the siege mounted by allied forces on land contributed to the Paraguayan decision to abandon Humaitá. Such events probably prompted the Paraguayans to draw up plans to assault the other ships anchored between Humaitá and Curupayty. The first movement occurred shortly after the passage on 19 February, when a fleet of 40 canoes tried to board the Brazilian monitor Alagoas but failed. The Paraguayans again attempted an assault, this time against two battleships, Cabral and Lima Barros, on 2 March, but once again failed after being repelled by the ships' crews and support from other vessels. After this latter failure, López ordered the abandonment of Humaitá with over 12,000 troops the following day.
These last Paraguayan actions led the Brazilian naval command to suspect that a new boarding attempt could occur against ships that were ahead of Humaitá. Indeed, several Paraguayan prisoners, including officers, reported that Solano López was training soldiers from various divisions of the army and navy, known as bogavantes, to board and seize imperial battleships. Second sergeant of the Paraguayan 12th Cavalry Regiment, Evaristo Chamorro, a prisoner since 9 June, reported that López wanted to assault the monitor Rio Grande, anchored in the Tagy ravine, with a force under the command of an ensign who participated in the assault on 2 March. After the battle at Tagy, second sergeant José Fructo Guerrero, another Paraguayan prisoner, confirmed the information given by Chamorro. This account demonstrated that the allies knew an attack on Tagy was expected, but did not know when it would happen.
Witnesses from the Paraguayan side such as George Thompson and Juan Crisóstomo Centurión agree that, when attacking the battleships, the Paraguayans intended to somehow protect the fortress of Humaitá. Soon after the passage of Humaitá by Brazilian ironclads, the siege by the allied troops, the occupation of the Chaco and the abandonment by López, Humaitá was completely unable to receive supplies. Still, the remaining Paraguayan forces wanted at all costs to keep the fortress in their possession. There is also the argument that López wished to obtain these battleships for himself in an attempt to reverse the course of the war in his favor. Another reason would be a kind of revenge by Solano López for the fact that Brazil bought the five battleships that were originally ordered by Paraguay, but that were not delivered due to non-payment by the Paraguayan government, as López knew that his navy was deficient from the beginning. Whatever it is, the approach was based on the principle of taking only one vessel: the monitor Rio Grande.
On 5 July, a conference was held between general Bernardino Caballero, commander of the Timbó fort, and Solano López to report that the bogavante forces were heading from the Chaco to the Bermejo River, from where they would depart to assault the ships, since the mouth of that river was located very close to Tagy. The Brazilian naval command began to receive reports, mainly from Paraguayan deserters, that Paraguayan forces could attack the Brazilian lines coming from the fortifications at Tebicuary. To protect the Tagy ravine, the monitor Rio Grande was ordered to anchor at that position in order to fire at any enemy incursions there. The other five battleships that had passed Humaitá began to bomb this position and Timbó, in addition to serving to transport troops and supplies for the allied forces in the Chaco and also in Tagy. It was during this period that the naval command received information from officer Chamorro about the battleships' boarding preparations.
The bogavantes, as the assault forces were called, were trained in a region that was in the upper part of the mouth of the Tebicuary River in a place where the Paraguay River had a channel. There, they practiced the assault with some wooden steamers that were anchored. These soldiers were drawn from infantry, cavalry and navy units, always soldiers who had a good reputation with their superiors, good swimmers and daring. The place destined for the assault, Tagy, was a ravine erected on the left bank of the Paraguay River. The Paraguayans had garrisoned that position with several cannons in order to try to neutralize the action of the Imperial Navy in that region of the river. However, by that time, such position was already under Brazilian control.
Imperial Army positions existed around the ravine, in addition to a telegraph line that linked the Brazilian base camp to that region. There are few sources that clearly demonstrate the details of the Paraguayan movements before the assault on the battleships. Days before the final attack on 9 July, from 6 to 8 July, the battleships Barroso and Rio Grande were not in Tagy, as they were replenishing their supplies and bombing Timbó. However, on the ninth, both vessels were located by the Paraguayans near Tagy.
Brazilian vessels had a vulnerability that facilitated the assault: their low freeboard. The ironclad Barroso, commanded by Artur Silveira da Mota, later Baron of Jaceguai, had a little more than one meter of freeboard, which decreased even further when the ship had to use its cannons, since about half of the edge was removable, reaching just over 60 centimeters the distance between the main floor and the water line. The Rio Grande belonged to a class of ships specifically designed with low freeboard. This characteristic of the ships allowed for an easier boarding. One resource that could be used was the anti-boarding net, very common on wooden ships at the time. However, if this protection was installed on the battleships it would prevent the use of their weapons, since if used it would destroy the net itself. The most viable solution was to intern the entire crew inside the vessel and carry out the defense from there.
The boarders numbered 270 men divided into two divisions of 20 canoes, under the command of major Francisco Lino Cabriza. The Paraguayans used aquatic plants in an attempt to camouflage their approach. The flood period contributed positively to this deception, since the sighting of such plants down the river was common. At 11:50 pm, the first elements of the Paraguayan divisions were sighted by the garrison of Barroso, which totaled 149 crewmen and officers, who were not being taken by surprise due to officer Alfredo Pereira de Araújo Neves acting in advance by suspecting the possible enemy movement against the vessels. However, the Paraguayans managed to surround the ship before the first shot. The assailants jumped on the battleship's deck armed with hand grenades, spears, pikes, hatchets and tubes loaded with asphyxiating materials. As they climbed aboard, they prevented the anchor from being hoisted, perhaps in an attempt to prevent the Barroso from moving and prostrating further below the site and getting close enough to being targeted by the army batteries and the Rio Grande that had not yet been boarded.
The entire Barroso garrison fought the assailants, but a detail that contributed to a more effective defense was that the vessel had a defensive structure called the bulwark above its casemate, from which seven men were garrisoned during the entire battle. If the bogavantes took this position, it would not be possible for the garrison inside the vessel to fight them. The small force above the casemate had a clear path to hit the invaders, unlike the inside crew that could only attack through existing openings. Still, they managed to inflict casualties on the enemy. The commander of Barroso decided to use the forward guns of the battleship only when a considerable number of bogavantes occupied the deck, since after firing the pieces needed men outside for the reloading work, that is, they would hardly be used again. At one point in the engagement, thirty Paraguayans crowded the bow and a single shot from the 120-caliber cannon "was enough to sweep the deck, where only dead bodies or severely wounded remained." The situation was repeated in the stern, which had two cannons loaded, where survivors and others still in the canoes engaged.
Despite the bogavantes
Some of Barroso
The defeat of the Paraguayans allowed the allies to prepare to take the fortress of Humaitá. About ten days after the battle, Imperial troops reinforced the Chaco and consequently opened the way for the transposition of the fortress by three more Imperial ships. One of the Paraguayan prisoners that took part in the assault indicated the defensive positions in the Tebicuary region, resulting in the transposition of three battleships on them and subsequent bombing of the bogavantes training site. On 24 July, Humaitá was finally abandoned by its last defenders, it was then occupied by troops under the command of the Marquis of Caxias the following day.
The remaining fleeing forces were found and cornered by the Brazilians on Isla Poí, towards the Chaco. Even at a disadvantage, the Paraguayans offered fierce combat in canoea and only surrendered with the arrival of Imperial army troops garrisoned at Timbó, which took place on 5 August. The assault attempt on 9 July was the third undertaken by the Paraguayans until that point, and a fourth one took place the following year, during the Campaign of the Hills.