Battle of Curupayty The Battle of Curupayty was a key battle in the Paraguayan War . On the morning of September 22 , 1866 , the joint force of the Imperial ( 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 Brazilian Navy failure was crucial at the later ground battle result . 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 Paraguayan War was limited because its military leader Francisco Solano López didn ' t 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 . Naval Bombardment . The September 22 attack was launched against Paraguayan strength . The Imperial fleet , advancing from Curuzú , consisted of five ironclads , 2 vessels bombers , 3 flat bombers and 6 gunboats led by Admiral Joaquim Marques Lisboa , Marquis of Tamandaré . The ironclads Bahia and Lima Barroso would be advanced to bombard the fortifications while the rest of the ships attacked the rest of the enemy lines . The shelling started in the morning , at 8 : 00 am , when 101 guns attacked the imperial fleet Paraguayan positions . They responded with artillery located toward the river . In a few hours about 5 , 000 shells were fired cons Paraguayan trenches . When it was noon , the battleships " Brazil " , " Lima Barroso " and " Tamandaré " crossed the line containing the battery Curupayty to strafe Paraguayan Canyon from his rear , terminating the bombing . Ally Land Attack . Bartolomé Mitre , warned that the Imperial fleet had finished his cannonade and assuming that the Paraguayan positions were to be destroyed , he ordered the advance . Argentines and Uruguayans were commanding generals and Paunero Wenceslao Emilio Mitre and Brazilians were commanded by Manuel Marques de Souza III , Baron of Porto Alegre . All these forces began the attack divided into 28 bodies , reinforced later by 15 battalions Argentines and Brazilians nine bodies were in reserve . In response , the Paraguayan General José Hedwig Diaz ordered the withdrawal of troops stationed in the trenches more advanced . The slaughter ally Only when Allied soldiers were within reach , Diaz ordered the artillery fire was almost intact Paraguayan and caused heavy casualties to the enemy troops advancing in dense formations and with much effort and slow due to the muddy area . These forces , to overcome the area swept by the artillery had to go through ditches covered with thorns and stakes to get to the shooting of Paraguayan infantry entrenched in their positions . Allied soldiers could not get close to the enemy trenches , and the few that managed to do was literally shot . When trying reinforcements back the reload was also being rejected in all attacks . Withdrawal . About 16 : 00 , Mitre gave the order to retire , although several troops had already begun the process on their own . Half an hour later the Paraguayans began to celebrate their victory .