Gerboise Verte was meant to be the green jerboa, the fourth in a series named for the desert rodent, though green broke from the tricolor pattern of the first three. It was fired at the Centre Saharien d'Expérimentations Militaires, about fifty kilometers south of Reggane at Hammoudia, on the southern rim of the Grand Erg Occidental. Yet the test that history remembers as a footnote of the Algiers putsch was, by most accounts, a technical failure, yielding only about one kiloton. Precautions were skipped in the rush. The physicist Yves Rocard recorded that no proper weather checks were made, which is how France came to set off a nuclear weapon inside a sandstorm.

What followed was, by today's standards, indefensible. As in an earlier test, the army staged a maneuver code-named Garigliano to learn how soldiers and armored vehicles could fight after a nuclear blast. Conscripts, young men doing their compulsory service, were the subjects. Shortly after detonation they were sent into the contaminated zone, sheltering in manholes about 800 meters from ground zero or riding in trucks across the irradiated sand. France's own records describe their measured doses as low, mostly a few millisieverts, well under the limits of the day. But the soldiers were not volunteers in any meaningful sense, and they were exposed deliberately, to see what would happen. Many would spend the rest of their lives wondering what those minutes in the desert had done to them.

Some stories from Reggane hardened into legend. The most enduring is that the whole bomb was driven the 1,500 kilometers from the port of Algiers to the desert in a Citroen 2CV, the tinny little workhorse of postwar France. The truth is stranger and smaller: by the accounts of those involved, only the plutonium pit, the bomb's radioactive heart, made part of the journey by 2CV, and only on the final night, between Reggane and the test center. Still, the image lingers, the most dangerous object in the French arsenal rattling across the Sahara in a car you could lift by the bumper.

The strangeness of Gerboise Verte has kept it alive in French memory. The novelist Christophe Bataille drew on the test for his 2015 story L'Experience, and the satirical television series A Very Secret Service staged the episode for comedy in its second season. The humor sits uneasily against the record. Behind the absurd image of a bomb in a 2CV, behind the punchline of a coup-week detonation, are conscripts sent into fallout and Saharan families left with a poisoned desert. France got its fourth bomb out of reach of the rebels. The people downwind got the consequences.