Brazilian monitor Piauí The Brazilian monitor " Piauí " was the fourth ship of the river monitor s built for the Brazilian Navy during the Paraguayan War in the late 1860s . " Piauí " passed the fortifications at Humaitá in July 1868 and provided fire support for the army for the rest of the war . The ship was assigned to the Mato Grosso Flotilla after the war . " Piauí " was scrapped in 1893 . 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 since a turreted design did not have the same problems engaging enemy ships and fortifications as did the central battery ironclads 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 of and displaced . With only of freeboard they had to be towed between Rio de Janeiro and their areas 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 . " Piauí " had a single 120 - pounder Whitworth rifled muzzle loader ( RML ) in her gun turret . The gun had a maximum range of about . Its shells weighed and the gun itself 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 , with the grain of each layer at right angles to the next layer . 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 rectangular gun turret had 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 . " Piauí " 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 8 January 1868 and commissioned later that month . Together with the ironclads and , " Piauí " passed the weakened Paraguayan fortifications at Humaitá on 21 July 1868 . She bombarded Asunción that same day . The monitor and a number of Brazilian ironclads bombarded Paraguayan batteries at Angostura , downstream of Asunción , on 28 October , 19 November and 26 November . " Piauí " , together with her sister ships and , broke through the Paraguayan defenses at Guaraio on 29 April 1869 and drove off the defenders . On 31 August 1869 the monitor unsuccessfully tried to locate and destroy the remnants of the Paraguayan Navy on the Manduvirá River . In the 1880s the ship ' s armament was reinforced with a pair of machine guns . After the war she was assigned to the Mato Grosso Flotilla and was scrapped in 1893 .