When General Franco launched his right-wing rebellion against the government in July 1936, Carrero, a professor at the Naval War College in Madrid, fled to the Nationalist (pro-Franco) zone, where he served during the Spanish Civil War (1936–1939). In 1939 he was promoted to chief of operations for the Naval General Staff. Franco promoted Carrero to vice admiral in 1963 and admiral in 1966. In May 1941 Franco appointed Carrero undersecretary of the president, and from that point until his death he remained Franco's closest advisor.
After World War II, the victorious Allies and quasi-fascist Spain viewed each other with suspicion and hostility. As the Cold War progressed, however, Carrero encouraged Franco to pursue a rapprochement with the United States by emphasizing his regime's staunch anticommunist credentials. Spain quickly established close military, economic, and diplomatic ties with the United States and Western Europe as a result of Carrero's policies.
Franco designated Prince Juan Carlos as his successor in 1969, while Carrero was to keep the Falangist political order intact under the reinstated monarchy. In September 1967 Franco appointed Carrero vice prime minister and named him prime minister in June 1973. On 20 December 1973 the Basque separatist organization Euskadi ta Askatasuna (ETA, Basque Homeland and Freedom) assassinated Carrero by detonating a bomb under his car in Madrid. With Franco's ideological successor gone, the Spanish transition to democracy was greatly hastened after Franco himself died in 1975.
Preston, Paul. The Triumph of Democracy in Spain. New York and London: Methuen, 1986.