The Pará-class monitors were a group of six wooden-hulled ironclad monitors named after Brazilian states and built in Brazil for the Brazilian Navy during the Paraguayan War in the late 1860s. The first three ships finished,, and, participated in the Passagem de Humaitá in February 1868. Afterwards the remaining ships joined the first three and they all provided fire support for the army for the rest of the war. The ships were split between the newly formed Upper Uruguay and Mato Grosso Flotillas after the war. Alagoas was transferred to Rio de Janeiro in the 1890s and participated in the Fleet Revolt of 1893–94.
Design and description
The Pará-class river monitors were designed to meet the need of the Brazilian Navy for small, shallow-draft armored ships capable of withstanding heavy fire during the Paraguayan War, which saw Argentina and Brazil allied against Paraguay. The two foreign-built river monitors already in service drew enough water that they could not operate on the shallower rivers in Paraguay. The monitor configuration was chosen as a turreted design did not have the same problems engaging enemy ships and fortifications as did the casemate ironclads already in Brazilian service. The gun turret sat on a circular platform that had a central pivot. It was rotated by four men via a system of gears; 2.25 minutes were required for a full 360° rotation. A bronze ram was fitted to these ships as well. The hull was sheathed with Muntz metal to reduce biofouling. The ships measured long overall, with a beam of. They had a draft between of and displaced. With only of freeboard they had to be towed between Rio de Janeiro and their area of operations. Their crew numbered 43 officers and men.
Propulsion
The Pará-class ships had two direct-acting steam engines, each driving a single propeller. Their engines were powered by two tubular boilers at a working pressure of. The engines produced a total of which gave the monitors a maximum speed of in calm waters. The ships carried enough coal for one day's steaming.
Armament
The first three ships carried a single 70-pounder Whitworthrifled muzzle loader in their gun turret, but the last three ships substituted a 120-pounder Whitworth RML. The 70-pdr gun had a maximum elevation of 15°, but the larger gun's elevation was reduced because of its longer barrel. Both guns had a similar maximum range of. The 70-pdr gun weighed and fired a shell that weighed. The shell of the 120-pdr gun weighed while the gun itself weighed. Most unusually the guns' Brazilian-designed iron carriage was designed to pivot vertically at the muzzle; this was done to minimize the size of the gunport through which splinters and shells could enter.
Armor
The hull of the Pará-class ships was made from three layers of wood that alternated in orientation. It was thick and was capped with a layer of peroba hardwood. The ships had a complete wrought iron waterline belt, high. It had a maximum thickness of 102 millimeters amidships, decreasing to and at the ship's ends. The curved deck was armored with of wrought iron. The gun turret was shaped like a rectangle with rounded corners. It was built much like the hull, but the front of the turret was protected by of armor, the sides by 102 millimeters and the rear by 76 millimeters. Its roof and the exposed portions of the platform it rested upon were protected by 12.7 millimeters of armor. The armored pilothouse was positioned ahead of the turret.
Construction
Service
The first three ships finished, Pará, Alagoas and Rio Grande, participated in the Passagem de Humaitá on 19 February 1868. For the engagement the three river monitors were lashed to the larger ironclads in case any engines were disabled by the Paraguayan guns. led with Rio Grande, followed by with Alagoas and with Pará. Both Alagoas, which had taken an estimated 200 hits, and Pará had to be beached after passing the fortress to prevent them from sinking. Alagoas was under repair at São José do Cerrito until mid-March, although Pará joined a squadron to capture the town of Laureles on 27 February. Rio Grande continued upstream with the other undamaged ships and they bombarded Asunción on 24 February with little effect. On 23 MarchRio Grande and Barroso sank the Parguayan steamer Igurey and both ships were boarded by Paraguayan soldiers on the evening of 9 July, although they managed to repel the boarders. For the rest of the war the river monitors bombarded Paraguayan positions and artillery batteries in support of the army, notably at Angostura, Timbó and along the Tebicuary and Manduvirá Rivers. After the war the ships were divided between the newly formed Upper Uruguay and Mato Grosso Flotillas. Alagoas was transferred to Rio de Janeiro in the 1890s and participated in the Fleet Revolt of 1893–94. The ships were disposed of during the last two decades of the 19th century, although Rio Grande was docked for reconstruction in 1899. However, the work was never completed and she was eventually scrapped in 1907.
