Pará-class monitor

The Pará-class monitors were a group of six wooden-hulled ironclad monitors named after Brazilian provinces and built in Brazil for the Imperial Brazilian Navy during the Paraguayan War in the late 1860s. The first three ships finished, BRAZILIAN MONITOR Pará, BRAZILIAN MONITOR Alagoas and BRAZILIAN MONITOR Rio Grande, participated in the Passage of 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 (Alto Uruguai) and Mato Grosso Flotillas 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 monitors 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 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 39 m long overall, with a beam of 8.54 m. They had a draft between of 1.51 - 1.54 m and displaced 500 t. With only 0.3 m 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 1.3 m propeller. Their engines were powered by two tubular boilers at a working pressure of 59 psi. The engines produced a total of 180 ihp which gave the monitors a maximum speed of 8 kn 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 5540 m. The 70-pdr gun weighed 8582 lb and fired a 5.5 in shell that weighed 81 lb. The 7 in shell of the 120-pdr gun weighed 151 lb while the gun itself weighed 16660 lb. 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 457 mm thick and was capped with a 102 mm layer of peroba hardwood. The ships had a complete wrought iron waterline belt, 0.91 m high. It had a maximum thickness of 102 millimeters amidships, decreasing to 76 mm and 51 mm at the ship's ends. The curved deck was armored with 12.7 mm 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 152 mm 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 history
The first three ships finished, Pará, Alagoas and Rio Grande, participated in the Passage of 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. BRAZILIAN IRONCLAD Barroso led with Rio Grande, followed by BRAZILIAN MONITOR Bahia with Alagoas and BRAZILIAN IRONCLAD Tamandaré 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 Rivers. 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 1893–1894. The ships were disposed of during the last two decades of the 19th century, although Rio Grande was docked for reconstruction in 1899. The work was never completed and she was eventually scrapped in 1907.