Brazilian ironclad Rio de Janeiro The Brazilian ironclad " Rio de Janeiro " was an armored gunboat ( Nr . 3 ) built for the Brazilian Navy during the Paraguayan War in the mid - 1860s . Like the other two gunboats she was built in Brazil and was designed as a casemate ironclad . Commissioned in April 1866 , the ship did not enter combat until September , when she bombarded Paraguayan fortifications at Curuzu . " Rio de Janeiro " hit two mines on 2 September and rapidly sank , taking 53 of her crew with her . Design and description . " Rio de Janeiro " was designed to meet the need of the Brazilian Navy for a small , simple , shallow - draft armored gunboat capable of withstanding heavy fire . A casemate ironclad design was chosen for ease of construction and a bronze ram , long , was fitted . The hull was sheathed with Muntz metal to reduce biofouling . For sea passages the ship ' s freeboard could be increased to by use of removable bulwarks high . On riverine operations , the bulkwarks and the ship ' s masts , were usually removed . The ship measured long overall , with a beam of and had a mean draft of . " Rio de Janeiro " normally displaced and at deep load . Her crew numbered 148 officers and men . Propulsion . " Rio de Janeiro " had a single John Penn & Sons 2 - cylinder steam engine driving a single 2 - bladed propeller . Her engine was powered by two tubular boilers . The engine produced a total of which gave the ship a maximum speed of . The ship ' s funnel was mounted directly in front of her casemate . " Rio de Janeiro " carried enough coal for six days ' steaming . Armament . " Rio de Janeiro " mounted two 70 - pounder Whitworth rifled muzzle loader s and two 68 - pounder smoothbore guns in her casemate . To minimize the possibility of shells or splinters entering the casemate through the gunports they were as small as possible , allowing only a 24° - arc of fire for each gun . The rectangular , casemate had two gun ports on each side as well as the front and rear . The 70 - pounder gun weighed and fired a shell that weighed . The gun had a maximum range of . The solid shot of the 68 - pounder gun weighed approximately while the gun itself weighed . The gun had a range of at an elevation of 12° . All of the guns could fire both solid shot and explosive shells . Armor . The hull of " Rio de Janeiro " was made from three layers of wood , each thick . The ship had a complete wrought iron waterline belt , high . It had a maximum thickness of covering the machinery and magazine s , elsewhere . The curved deck , as well as the roof of the casemate , was armored with of wrought iron . The casemate was protected by 102 millimeters of armor on all four sides , backed by of wood capped with a 102 mm layer of peroba hardwood . Service . " Rio de Janeiro " was laid down at the Arsenal de Marinha da Côrte in Rio de Janeiro on 28 June 1865 , during the Paraguayan War , which saw Argentina and Brazil allied against Paraguay . She was launched on 18 February 1866 and completed on 1 March 1866 . Commissioned in April she reached the combat zone on 4 May . The ship reached Corrientes , with the ironclad , in July 1866 . On 1 September " Rio de Janeiro " bombarded the Paraguayan fortifications at Curuzú in company with the other Brazilian ironclads . A 68 - pounder shell entered one of her gunports during the bombardment , killing four men and wounding five . The next day , after her damage was repaired , the ship struck two mines in the Apa River while trying to rendezvous with the other Brazilian ironclads bombarding Curupaity . " Rio de Janeiro " sank instantly with the loss of 53 of her crew . She remains there , entombed under some of sand .