The Copacabana Fort revolt, (Revolta do Forte de Copacabana) also known as the 18 of the Fort revolt (Revolta dos 18 do Forte), was one of several movements coordinated by rebel factions of the Brazilian Army against the president of Brazil, Epitácio Pessoa, and Artur Bernardes, winner of the 1922 presidential election, on 5 July 1922. Acting under the figure of marshal Hermes da Fonseca and supporting the defeated faction, the Republican Reaction, the rebels tried a wide revolt in Rio de Janeiro, but only managed to control Fort Copacabana and the Military School of Realengo, in addition to, outside the city, a focus in Niterói and the 1st Military Circumscription, in Mato Grosso. They were defeated, but the revolt marks the beginning of tenentism and the events that led to the end of the First Brazilian Republic.
In 1921, Nilo Peçanha launched himself as an opposition candidate, aligning the oligarchies of second importance states against the domination of Brazilian politics by the most powerful states of São Paulo and Minas Gerais. Peçanha enlisted the support of dissident military members gathered around Hermes da Fonseca, president of the Military Club. In October, false letters attributed to Artur Bernardes with offenses to the military stirred up the election and the military participated actively in the campaign. The manipulated electoral system ensured the situationist victory in March 1922. The opposition contested the results and over the following months a military conspiracy emerged across the country to remove Epitácio Pessoa and prevent the inauguration of Artur Bernardes. It drew great enthusiasm from tenentes (lieutenants), but few senior officers. The rebels did not have a project for society, being at first a movement of reparation, but even so they reflected dissatisfaction with the regime. In early July, the revolt met with the closure of the Military Club and the brief arrest of Hermes da Fonseca for his public opposition to the government's interference, using the Army, in the election in Pernambuco.