When Leoncio Prado was 26 years old, the war with Chile broke out in 1879, the so-called War of the Pacific, so the young officer returned to Peru to defend his country. He participated in the Navy and later in the Army. First, he was entrusted with the organization of a torpedo boats that was to act on the island of Alacrán in the port of Arica against the Chilean naval forces. Later, integrating the Army of the South in 1880, he was commissioned to form a military body with which he participated in the Battle of Tacna in May. Following the Peruvian defeat in that battle, he led a Guerrilla warfare around Tacna, until he was captured by the Chileans at Tatara in July. But then he was released on condition of not fighting in the war again, which he did not comply with. He later participated in the Sierra campaign, dying shortly after the Battle of Huamachuco in 1883.