The 18 of the Copacabana Fort revolt occurred on July 5, 1922, in the city of Rio de Janeiro, then the Federal District of Brazil. It was the first revolt of the tenentista movement, in the context of the Brazilian First Republic.
Tenentismo is the political-military movement of various rebellions by young officers (mostly lieutenants) of the Brazilian army that occurred during the 1920s. The tenentes called for reforms in the power structure. Among these reforms was the end of the cabresto vote (a tool of political control through the abuse of authority, the buying of votes, the use of public institutions, violence, ghost voting, exchange of favors, and fraud). Other goals included the institution of a secret ballot, and the reform of public education.
In 1922 until 1930, the tenentes constituted a minority in the officer corps. Their number was around 325, consisting of officers who graduated from Brazil's Escola Militar do Realengo. By 1930, the number of these tenentes exceeded 600 or about 11 percent of the 5,255-strong officer corps on active duty. Although the 1922 revolt at Copacabana fort ended in failure, the sheer audacity by which the small band of rebels attacked a much larger force captured the attention of the public and inspired similar movements by the tenentes later on. Some sources maintained that the uprising was doomed from the start because authorities, including the Brazilian president, knew of the plot. The officers involved were also said to have accepted death. These factors contributed to the way the rebels emerged as martyrs especially for their fellow soldiers.
The Army reasoned that itself was the only force capable of saving the Republic. As a result, the movement was based in only one part of society, the army, and this isolated the Tenentista movement from the rest of the society.
On October 3, 1919, a civilian - João Pandiá Calógeras - was designated as War Minister for the first time in the history of the Brazilian Republic by President Epitácio Pessoa. Calógeras held this post until November 15, 1922.
In 1921, the Correio da Manhã (Brazil), a Brazilian newspaper published in Rio de Janeiro from 1901 to 1974, published letters supposedly written by Artur Bernardes (Brazilian president from 1922 to 1926) and Raul Soares, a Brazilian politician who was Navy Minister during Epitácio Pessoa's government and Secretary of the Interior during Artur Bernardes' government. These letters included insults directed at the Army and Marshal Hermes da Fonseca; the Brazilian president from 1910 to 1914, and one of the most important figures in the Army during Epitácio Pessoa's and Artur Bernardes' governments. It was later found that the signatures in the letters were forged.
In 1922, Artur Bernardes (supposed author of the letters published in 1921) won the Presidential elections. The Militar Club, a traditional military college in Rio de Janeiro, and Borges de Medeiros, a famous Brazilian politician and lawyer, asked for the creation of a court to review the election results. However, the elections were recognized by the Congress, so the court was never created.
In June 1922, Epitácio Pessoa intervened in the state of Pernambuco's elections, and this act was strongly criticized by Marshal Hermes da Fonseca. As a reaction, Epitácio ordered Marshal Hermes da Fonseca's arrest and the closure of the Militar Club.
The revolt was supposed to include supporters in many military bases, but only a few joined in: Fort Copacabana, at Copacabana, some marginal elements from the Military village, Vigia Fort, the Realengo Military School, the 1st Engineering Battalion, navy and army members, and the 1st Military Division. The response of pro-tenentistas was weak because the government received notice that the revolt would happen and removed the crucial pro-tenentista officers from the most important military bases.
The Fort Copacabana rebels fired their cannons against many important government and military bases during the early morning of the 5th. Throughout the rest of the day, the fort was bombed. In the early morning of the 6th, Captain Euclides da Cunha and Lieutenant Siqueira Campos permitted any soldiers who wanted to leave the fort to do so; 273 of 301 left the Fort. Meanwhile, a destroyer and two battleships took up positions near the Fort and started to shell it. Captain Euclides Hermes left to negotiate, but was arrested. The government's last word to the rebels was an order to either surrender or be destroyed. The Tenentistas still inside the Fort then cut a Brazilian flag in 29 pieces, one for each rebel, and decided to march to the Catete Palace, the head office of the Executive Power. Most of them dispersed and only 24  were left (a civilian joined then to form this number). Walking down Avenida Atlantica next to the beach, they met a combined force of loyalist troops and police at the intersection of Avenida Atlantica and the street now renamed Rua Siqueira Campos in the middle of Copacabana. Only Lieutenants Siqueira Campos and Eduardo Gomes along with four other rebels survived. A photograph first published in the daily, O Malho shows eighteen rebels. For that reason, the public still erroneously refers to those who took part in the battle on the insurgent's side as "The Eighteen of the Fort."
"As forças que estão sitiando o forte de Copacabana, sob o comando do general Mena Barreto, tiveram ordem do governo para enviarem um 'ultimatum' à fortaleza, intimando-a a render-se dentro de uma hora. Em caso contrário será bombardeada por forças legais de terra e navios de guerra." O Combate, 5 July 1922.
"Na Villa Militar só houve um pequeno movimento subversivo, imediatamente abafado. Um pelotão, às ordens de um tenente, atirou contra a sala onde estavam reunidos os oficiais. O capitão da companhia a que pertencia esse pelotão, de nome Barbosa Monteiro, oficial de extraordinário valor moral e intelectual, saiu ao encontro dos soldados sublevados e recebeu uma descarga que o fez tomar morto. O pelotão, imediatamente cercado pelo resto da companhia, que acudiu, foi, com seu comandante, feito prisioneiro e desarmado. (...)" A União, 9 July 1922.
"- Nunca desejei e nunca pensei ter de assinar um ato como este, mas agora o faço gostosamente, certo de que estou prestando um serviço à República e às instituições." A Pátria, 6 July 1922.
The Copacabana Fort revolt is depicted in a highly sympathetic way in an early chapter of The Knight of Hope (Portuguese: O cavaleiro da esperanca), Jorge Amado's 1942 biography of the well-known Brazilian revolutionary Luis Carlos Prestes.