Before the first test was conducted at Alamogordo, New Mexico, the nuclear bombmakers weren't even sure that the weapons could be detonated. Most of the scientists at Los Alamos grossly underestimated the power of the first bomb; Oppenheimer, for example, estimated that the yield would be three hundred tons, less than 2 per cent of the value actually achieved. Shortly thereafter, members of the scientific community were surprised again—many of them overwhelmed and sickened—when they saw the devastation at Hiroshima. And despite use against two cities and an ambitious testing program, the full danger of fallout wasn't identified until more than a decade later.