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.