Atomic Bomb On August 2, 1939 Albert Einstein wrote to President Franklin D. Roosevelt. This was right before the start of World War 2. In this letter Einstein and several other scientists told Roosevelt of the efforts Hitler was making to purify U-235 in which he hoped to make an atomic bomb. This is when the United States started the Manhattan Project. This was the project of making an atomic bomb. In the project many brilliant minds were used. The most famous of these people is Robert Oppenheimer. He was the major person behind this project. He basically ran the operation and oversaw the hole project from start to completion. Other great people like H.C. Urey, Ernest Lawrence, Isi