Like its predecessor, the bomb took its name from the jerboa, the bounding desert rodent the French call gerboise. White was the second color of the tricolor, after blue. The device weighed 1,250 kilograms and was filled with plutonium, and it was fired at 6:17 in the morning with a yield of three kilotons. That number was no accident. France wanted to show its scientists could miniaturize an atomic weapon, shrinking it from an unwieldy first-generation monster toward something that could ride a missile or sit in the belly of a bomber. Smaller was the whole point.

There was a practical reason Gerboise Blanche was set off where it was. Rather than reuse the contaminated ground from the first shot, the authorities placed this bomb a few kilometers from the original ground zero, on a purpose-built concrete pad. They feared that the original site was already too radioactive for the tests still to come. It was a telling decision. The desert that France publicly described as harmlessly empty was, by its own engineers' reckoning, too poisoned to stand on twice.

For all its modest yield, Gerboise Blanche left an outsized footprint. A French National Assembly report in 2001 found that while the fallout from the other three Reggane tests stayed within tidy circles less than a kilometer across, the contamination from Gerboise Blanche spread to the southwest for more than six kilometers. The smallest bomb of the series dirtied the largest swath of ground. The numbers in such reports are antiseptic, but the sand they describe was not empty. People herded animals, drew water, and raised children within reach of that drifting plume, most of them never knowing what the wind had laid down around them.

France hailed the test as a success. The Ministry of the Armed Forces declared that Gerboise Blanche had opened the way to miniaturizing nuclear weapons, a crucial step toward the force de frappe, the independent strike force that would become the backbone of French defense for the rest of the century. The crater the bomb dug was later filled in, the pad abandoned to the wind. What looked from Paris like a clean technical milestone looked very different from the oases downwind, where the costs of France's atomic ambition would surface slowly, in clinics and in cemeteries, for decades to come.