Another great naval battle occurred in 1868; the Passage of Humaitá which was an operation of riverine warfare − the most lethal in South American history − in which a force of six Brazilian Navy armoured vessels was ordered to dash past under the guns of the Fortress of Humaitá on the Paraguay River. Some competent neutral observers had considered that the feat was very nearly impossible. The purpose of the exercise was to stop the Paraguayans resupplying the fortress by river, and to provide the Allies with a much-needed propaganda victory after 4 years of an exhaustive war. The attempt took place on 19 February 1868 and was successful, restoring the reputation of the Brazilian navy and the Empire of Brazil's financial credit, and causing the Paraguayans to evacuate their capital Asunción. Some authors have considered that it was the turning point or culminating event of the war. The fortress, by then fully surrounded by Allied forces on land or blockaded by water, was captured on 25 July 1868.