The Manhattan Project

Since the late 1930s, scientists had been exploring the military applications of atomic energy. German scientists split the atom in a laboratory experiment as early as 1938. The next year, Albert Einstein, a leading physicist who had emigrated from Germany to the United States to flee the Nazis, warned President Roosevelt that a new atomic weapon might be possible. Alarmed by the outbreak of war in Europe, Roosevelt authorized an American effort to develop the first atomic bomb before the Germans did. Code-named the Manhattan Project, it was placed under the leadership of Col. Leslie R. Groves of the U.S. Army Corps of Engineers. 

Scientists predicted that fission fuel could be derived from uranium 235, an isotope of uranium, and from plutonium, a uranium by-product that could be produced from atomic reactors. Before long, the Manhattan Project constructed several facilities for production of an atomic bomb. Among them were Oak Ridge, Tennessee, where huge equipment separated uranium 235 from uranium 238 ore; Hanford, Washington, where reactors produced plutonium; and Los Alamos, New Mexico, where the bomb itself was designed. 

The Twentieth Air Force’s fleet of B–29s offered the obvious delivery vehicles because they were capable of dropping the new weapons where they would have the greatest effect. In December 1944, long before the first bomb was ready for testing, the Army Air Forces activated the 509th Composite Group, with specially designed B–29s, under Col. Paul W. Tibbets, Jr. After training at Wendover Field, Utah, the group moved to North Field, Tinian, in May 1945. Most of the 509th’s members did not know about the atomic bomb until the first mission, having been told only to prepare for the delivery of special devices over selected Japanese targets. 

At Los Alamos, American physicist J. Robert Oppenheimer led a team of scientists designing the first atomic weapon. In two years, his team invented two kinds of atomic bombs: “Little Boy,” a uranium 235 bomb that used a gun detonator; and “Fat Man,” a plutonium bomb that used an implosion detonator. Both bombs operated on the same principle—force enough nuclear material in a small enough space to achieve a critical mass that would produce an atomic chain reaction. The resulting explosion would dwarf any that humankind had ever achieved.

 Only when Truman succeeded to the presidency in April 1945 did he learn the details of the Manhattan Project. Despite the surrender of Germany in May, Truman directed that the Manhattan Project proceed, and by mid-July the first atomic bomb was ready for testing. Engineers put one of the plutonium Fat Man bombs on a one-hundred-foot steel tower at a site called Trinity at the Alamogordo Bombing Range, about 200 miles south of Los Alamos. On July 16, 1945, the bomb exploded with a blast equivalent to 17,000 tons of TNT.