Luis Carrero Blanco was not a politician in the conventional sense. A career naval officer who rose to admiral, he had served Franco with rigid loyalty since the Civil War. By 1973, the aging dictator -- then 80 years old and visibly declining -- had appointed Carrero Blanco as president of the government, the first person other than Franco himself to hold the title since 1939. The appointment was widely understood as a succession plan: Carrero Blanco would maintain the Francoist system after Franco's death, ensuring continuity of the authoritarian regime. He was a hardliner who viewed any liberalization as weakness and any opposition as subversion. Just the day before his death, Carrero Blanco had met with U.S. Secretary of State Henry Kissinger, and both men had expressed concern about left-wing threats to the regime. A government meeting on the 'dangers of subversion threatening Spain' was scheduled for the day he died.

ETA -- Euskadi Ta Askatasuna, the Basque separatist organization -- named the plot Operacion Ogro. The planning was meticulous. Operatives rented a ground-floor apartment on Calle Claudio Coello and, posing as sculptors to explain the noise and dust, dug a tunnel beneath the street to a point directly under Carrero Blanco's daily route. The admiral's habits were rigid, almost inviting exploitation: he attended the same church every morning, traveled the same streets, at the same time. On the morning of December 20, the ETA cell detonated the charge as his car passed overhead. The explosion tore a crater in the street and sent the armored Dodge arcing over the Church of San Francisco de Borja to crash into a second-floor interior terrace of the Jesuit residence behind it. Carrero Blanco's driver and bodyguard were also killed.

Deputy Prime Minister Torcuato Fernandez Miranda's first act upon learning of Carrero Blanco's death was to call Franco and then declare himself acting prime minister without imposing a state of exception. This restraint proved decisive. The Director-General of the Civil Guard, Carlos Iniesta Cano, had already sent telegrams ordering agents to use deadly force in any confrontation. Fernandez Miranda forced him to reverse the order immediately, preventing a crackdown that could have ignited wider violence. The assassination removed the one figure who might have held the Francoist system together after the dictator's death. Without Carrero Blanco, the regime lacked a credible succession plan, and when Franco died two years later in November 1975, the path was open for King Juan Carlos I to steer Spain toward democratic transition. Some analysts have called the assassination the only action ETA ever took that genuinely advanced Spanish democracy, though former ETA member Jon Juaristi argued the goal was not democratization but destabilization.

Eva Forest, under the pseudonym Julen Agirre, published Operation Ogro in 1974, recounting the plot from the inside. The book became the basis for Gillo Pontecorvo's 1979 film of the same name. When it was republished twenty years later, a new chapter corrected deliberate misinformation from the first edition -- details that had been falsified to protect the escape routes of the perpetrators. The Dodge 3700 GT itself, the car that flew over a church, has been on display at the Spanish Army's Automobile Museum in Torrejon de Ardoz since 2014. A memorial plate marks the site on Calle Claudio Coello. Basque musicians Etxamendi and Larralde adapted Marty Robbins' country song 'El Paso' into 'Yup! la-la,' a song about the killing that became famous in the Basque Country by the late 1970s. The Spanish Association of Victims of Terrorism considers Carrero Blanco a victim of terrorism, a classification that places him in the same category as the hundreds of people ETA killed over the following three decades.