The Battle of Tuyutí was the biggest and bloodiest battle of the entire Paraguay War and the South American continent, as it involved more than 55,000 men. It was fought on May 24, 1866, in a swampy, sandy and difficult to move region called Tuyutí, in southwestern Paraguay. Paraguayan historians maintain that poor coordination and a lack of detailed planning turned a certain victory for their army into a devastating defeat. Without a well-defined chain of command and without knowing the terrain well, due to the absence of maps, the Triple Alliance encountered difficulties in the beginning of the action. In this historical simulation, we will consider a hypothesis in which both the Paraguayan attack had been better coordinated and the Allied defense had been better oriented – even though the latter maintained its expectation for the next offensive.