The Humaitá class was designed to meet the Paraguayan goal of achieving naval supremacy in the Paraguay River, given the conflict with Bolivia over the Chaco region.

Originally the vessels mounted two Vickers 40 mm autocannons and cranes and racks for lying mines, of which each gunboat carried six.

They entered the Atlantic after paying an unintended official visit to Gibraltar, where they were received by the battlecruiser HMS Renown, and sailed for Buenos Aires, Argentina, via Pernambuco in Brazil.

[1] The arrival of the vessels prompted yet another diplomatic protest from Bolivia, whose bilateral relations with Paraguay had been increasingly deteriorating due to the dispute over the Chaco region since 1928.

[6] The first operational mission of Humaitá was the deployment of a detachment of reservists to Puerto Casado, some 200 km (120 mi) from the frontline, in July 1932, barely a month after the beginning of the Chaco War with Bolivia.

[1] The first engagement against Bolivian aircraft took place near Puerto Leda on 22 December 1932, when two Vickers Vespas dropped a bomb and strafed Humaitá, only to be driven off.

The Commander-in-Chief of the army, General Estigarribia, hoped that the rate of fire and range of the 4.7 in twin guns would pound the defenses of Villa Montes to pieces from 22 km (14 mi) away, but the war was over before the plan could come together.

[12] During the 1947 Paraguayan civil war, the crews of Humaitá and Paraguay, at the time undergoing a major overhaul in Buenos Aires, took control of the vessels and arrested the officers loyal to president Higinio Morínigo.

Rebel personnel from Paraguay landed on the islands of Corateí and San Pablo, but they were eventually isolated and captured on 25 July by loyal troops carried by the transport ships Tirador and Capitán Cabral.

The gunboats were interned by Argentine authorities, and eventually handed over to the Paraguayan government in August, when the rebellion was finally crushed.

[13][14] In 1955, Paraguay became involved in the aftermath of Argentina's Revolucion Libertadora, when former president Juan Domingo Perón went into exile aboard the Paraguayan vessel.