Pará - class monitor The " Pará " class monitors were a group of six wooden - hulled ironclad s 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 Flotilla s 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 monitor s 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 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 . The first three ships carried a single 70 - pounder Whitworth rifled muzzle loader ( RML ) 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 . 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 March " Rio 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 River s . 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 .