The Pará-class monitors were designed to meet the need of the Brazilian Navy for small, shallow-draft armored ships capable of withstanding heavy fire. 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
Rio Grande carried a single 70-pounder Whitworthrifled muzzle loader in her gun turret. The 70-pounder gun had a maximum elevation of 15°. It had a maximum range of. The 70-pounder gun weighed and fired a shell that weighed. Most unusually the gun's 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.
Service
Rio Grande was laid down at the Arsenal de Marinha da Côrte in Rio de Janeiro on 8 December 1866, during the Paraguayan War, which saw Argentina and Brazil allied against Paraguay. She was launched on 17 August 1867 and completed on 3 September 1867. She arrived at Montevideo on 6 January 1868 and steamed up the Paraná River, although her passage further north was barred by the Paraguayan fortifications at Humaitá. On 19 February 1868 six Brazilian ironclads, including Rio Grande, sailed past Humaitá at night. Rio Grande and her two sister ships, and, 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. The latter two ships were damaged as they sailed past the fortifications and had to be beached to prevent them from sinking. Rio Grande continued upstream with the other undamaged ships and they bombarded Asunción on 24 February. On 23 MarchRio Grande and Barroso sank the steamer Igurey. Paraguayan soldiers in canoes attempted to board both ships on the evening of 9 July, but were only successful in getting on boardRio Grande where they were able to kill the ship's captain and some of the crew. The remaining crewmembers locked the monitor's hatches and Barroso was able to kill or capture almost all of the Paraguayans on deck. On 15 October she bombarded Angostura Fort in company with,, Pará and her sister. After the war Rio Grande was assigned to the newly formed Alto Uruguai Flotilla, based at Itaqui. She was docked in Ladário for rebuilding in 1899, but this was never completed and she was scrapped in February 1907.
