What Was the Manhattan Project? The Secret Program Behind the Atomic Bomb
Calutron operators at the Y-12 plant in Oak Ridge, Tennessee, during World War II. Photo: Ed Westcott / U.S. Army Manhattan Engineer District, public domain. Image record . During World War II, the Manhattan Project brought scientists, industry and a vast workforce together at secret sites to build the first atomic weapons. It pursued uranium and plutonium in parallel, culminating in the Trinity test in July 1945. Its legacy includes nuclear arms, displaced communities and radioactive waste. Why did the Manhattan Project begin? In December 1938, researchers in Germany discovered nuclear fission: the splitting of an atomic nucleus, which releases energy. Scientists soon recognized that a chain reaction might make a weapon of unprecedented power possible. In August 1939, physicist Leo Szilard drafted a warning that Albert Einstein signed and sent to President Franklin D. Roosevelt. The possibility that Nazi Germany might pursue such a weapon gave the warning urgency. The U.S. govern...