On December 6th, 1973, Massera was designated General Commander of the Argentine Navy by Decree 552, signed by President Perón and Minister Angel F. Robledo (published on the Boletín Oficial de la República Argentina on December 13th), and, on August 23rd, 1974 he was promoted to full Admiral by Decree Nr.

On June 15th, 1974, he, along with the commanders of the Army and the Air Force, accompanied then-Vice President Isabel Perón to Italy and Spain, where she met with Francisco Franco.

[7] Between 1976 and 1978 Admiral Massera was part, together with Jorge Rafael Videla and Orlando Ramón Agosti, of the military junta that deposed President Isabel Perón and ruled Argentina de facto during the National Reorganization Process.

[2] After the end of the dictatorship in 1983, he was tried for human rights violations and sentenced to life imprisonment and the loss of his military grade.

Massera was free until 1998 when he was imprisoned again pending an investigation of several instances of kidnapping and suppression of the identity of minors during his term, as well as orders of torture, execution, confinement in illegal detention centres, and drowning of prisoners.