In 1939 scientist Albert Einstein wrote a letter to U.S. President Franklin Roosevelt encouraging government funding for atomic and nuclear fission research for use in atomic weapons. His letter was prompted by rumors that Adolf Hitler and the Nazis were close to creating an atomic bomb. Roosevelt agreed and placed General Leslie Groves and physicist J. Robert Oppenheimer in charge of the Manhattan Project two years later. The name "Manhattan Project" was the code word for the development of the atomic bomb. On July 16, 1945, the first atomic bomb was tested at the Trinity Site in New Mexico. The weapon was later used against the Japanese to end World War II.