The explosion obliterated everything within its immediate radius and devastated a wide swath of the surrounding city. Among the buildings completely destroyed were the Asilo de Ancianos, an old age home, and the Casa Cuna orphanage, where 41 people died. A nearby factory lost 100 workers. Official figures at the time put the death toll at 150, later adjusted to 147, with 5,000 injured. But given the density of the neighborhoods destroyed and the types of buildings that were leveled -- residential blocks, care homes, workplaces full of people at that hour -- many sources believe the actual toll was considerably higher. The blast also destroyed an ancient Punic or Phoenician necropolis whose excavation had been featured in National Geographic magazine in 1924, erasing an archaeological treasure that had survived for millennia.

No official technical explanation was ever made public. The findings of a secret military inquest were never published, and all relevant documentation was later destroyed in a fire at the naval archive center. The circumstances fed persistent rumors of sabotage: the Spanish Maquis, anti-Franco guerrillas, were increasingly active at the time. Several witnesses reported seeing a small boat leaving the base in the dark before the explosion. The Spanish secret service had reportedly received intelligence that something was about to happen in Cadiz. And Franco himself did not visit the devastated city until several months later, a conspicuous absence for a dictator who typically appeared at scenes of national crisis. The regime's official press release offered a different theory: the mines were "from the Reds and Russian-made," and their instability was the cause.

The naval base that exploded carried its own hidden past. The shipyard on the site had signed a lucrative contract in the mid-1920s to supply the German Navy with German-designed torpedoes, and had even built a U-boat for testing and training. This clandestine cooperation between Spain and Weimar Germany, conducted in violation of the Treaty of Versailles, meant the base had been handling explosive ordnance of various national origins for decades. By 1947, the stockpile of 2,228 munitions -- mines, torpedoes, and depth charges -- distributed between two depots was enormous by any standard. Whatever triggered the explosion, the sheer scale of what was stored in a base adjacent to residential neighborhoods made catastrophe a matter of when, not if.

The aftermath of the explosion produced one of the strangest episodes of the Franco era. Cadiz had been famous for its carnival -- a raucous, satirical celebration with deep roots in the city's culture. Franco had banned it after the Spanish Civil War, considering the tradition too subversive for his authoritarian state. But the devastation of 1947 was so severe, the morale of the population so broken, that the regime made an extraordinary concession: it permitted the return of the carnival the following year. Unable to stomach the word "carnival," the regime christened the celebration "Fiestas Tipicas Gaditanas" and subjected the famous coplas -- the satirical songs that were the carnival's heart -- to strict censorship. It was a remarkable admission that the people of Cadiz needed something the regime could not otherwise provide: the right to sing, however constrained, about what had happened to them.