The U.S. government secretly hired hundreds of private companies during the 1940s and '50s to process huge volumes of nuclear weapons material, leaving a legacy of poisoned workers and contaminated communities that lingers to this day. From mom-and-pop machine shops to big-name chemical firms, private manufacturing facilities across the nation were quietly converted to the risky business of handling tons of uranium, thorium, polonium, beryllium and other radioactive and toxic substances. Few of the contractors were prepared for the hazards of their government-sponsored missions. Thousands of workers were exposed to dangerous levels of radiation, often hundreds of times stronger than the limits of the time. Dozens of communities were contaminated, their air, ground and water fouled by toxic and radioactive waste. The risks were kept hidden. In some cases, they have remained so. The full story of the secret contracting effort has never been told. Many of the companies that were involved have been forgotten, the impact of their operations unexamined for half a century. Yet their history carries profound implications for the thousands of people they employed, as well as for the thousands who lived - and still live - near the factories.