Answer: The Atomic Bomb
When the tests began on the atoll, news spread around the world, and the designer of the modern two-piece swimsuit learned that this was the case. French automobile engineer Louis Réard heard about Bikini Atoll. Réard was so sure that his design – which revealed more of belly and chest than the previous two-piece bathing suits – would gain in popularity as explosively as a nuclear bomb, calling it the bikini, alluding to the site of the nuclear tests.
Réard was right in the long run. In the short term, the design was considered scandalous. In fact, he could not even find a regular model in Paris to model the design for him. The woman shown here, Micheline Bernardini, was a nude dancer from the Casino de Paris, who gladly accepted in the summer of 1946 to promote the new swimsuit style. Part of the ad was the box she holds in the photo at the top: Réard's design was so small that the entire two-piece swimsuit could be tucked into the little box in her left hand.