The Battle of Curupayty was a key battle in the Paraguayan War. On the morning of September 22, 1866, the joint force of Brazilian, Argentine, and Uruguayan armies attacked Paraguayan fortified trenches on Curupaity. The Paraguayans were led by General José E. Díaz. This position was held by 5,000 men and 49 cannons, some of them in hidden places out of the attackers view. The Brazilian Navy gave support to the 20,000 assailants, but the ships had to keep some distance from the guns at the fortress of Humaitá, which led to the lack of accuracy and impact of the ship's fire. The navy's failure was crucial at the later ground battle result.: 61–62 The Paraguayans were also successful in misleading their foes: a trench drew most of the Brazilian fire, but the Paraguayan troops were located elsewhere. Around 20 percent of the almost 20,000 allied (Brazilian and Argentine) troops involved in the attack were lost; Paraguay lost less than a hundred men. The utter failure resulted in the change of the Allied command. Paraguay's biggest success in the ultimately disastrous war was limited because its military leader Francisco Solano López did not counterattack the defeated Allies; not even a general as celebrated as Díaz would attack without López's orders. Ultimately, the battle of Curupayty was merely a sidenote and temporary success in what would eventually become a near-extermination of the Paraguayan people.