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.