After a botched jailbreak in which several guerrilla leaders escaped to Chile while others were recaptured, military personnel took the remaining prisoners from their cells before dawn and shot them, killing sixteen. The massacre became a rallying symbol for Argentina's left and a preview of the state violence that would define the country's Dirty War later that decade.
The prisoners were members of three left-wing guerrilla organizations—the Trotskyist ERP, the Peronist FAR, and the Montoneros—held at a maximum-security prison in Rawson, Patagonia. On August 15, 1972, a coordinated escape attempt sprang the top guerrilla commanders, who reached a getaway plane and fled to Chile, then under Salvador Allende's leftist government. A second group of nineteen prisoners, delayed by traffic, missed the plane and surrendered to authorities at the nearby Trelew airport, reportedly under an agreement guaranteeing their safety.
Instead, the navy transferred them to the Almirante Zar naval air base. In the predawn hours, officers removed the prisoners from their cells, lined them up, and opened fire. Sixteen died; three survived by feigning death, later testifying in detail to what became known as the Trelew Massacre.
The killings, carried out under a military government already anxious about growing leftist insurgency, radicalized a generation of Argentine activists and became a foundational grievance for groups like the Montoneros. Investigators and historians later identified the massacre as a direct precursor to the systematic disappearances and extrajudicial killings that Argentina's 1976–1983 military dictatorship would carry out on a far larger scale.