In 1961 the 3rd Army ensured João Goulart's inauguration as president when its commander, General José Machado Lopes, participated with his forces in the Legality Campaign in alliance with the governor of Rio Grande do Sul Leonel Brizola. Machado Lopes left command in October 1961. The 3rd Army was again a factor in Goulart's favor in anticipating the referendum on parliamentarism in September 1962. Its commander at the time, General Jair Dantas Ribeiro, was the Minister of War in 1964. The command of the 3rd Army had been with General Benjamim Rodrigues Galhardo since August 1963.
