Brazilian monitor Rio Grande The Brazilian monitor " Rio Grande " was the second ship of the river monitor s built for the Brazilian Navy during the Paraguayan War in the late 1860s . " Rio Grande " participated in the Passagem de Humaitá in February 1868 and provided fire support for the army for the rest of the war . The ship was assigned to the Upper Uruguay ( ) Flotilla after the war . " Rio Grande " was scrapped in 1907 . Design and description . 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 ironclad s already in Brazilian service . The oblong 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 Whitworth rifled muzzle loader ( RML ) in her gun turret . The 70 - pdr gun had a maximum elevation of 15° . It had a maximum range of . The 70 - pdr 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 March " Rio 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 board " Rio 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 .