Harry S. Truman was the 33rd president of the United States of America. He became president because Franklin D. Roosevelt died while in office; Truman was Roosevelt's vice president at the time. Truman found himself facing some of the greatest challenges faced by any president of the 20th century. He discovered in July 1945 that some scientists working for the U.S. government had successfully tested an atomic bomb in New Mexico. President Truman wanted to use the atomic bomb to end the war in the Pacific, but with the least amount of American disaster. This decision was one of the most important decisions of the 20th century and extremely perplexing when analyzed. Harry S. Truman became the 33rd president upon the death of Franklin D. Roosevelt. President Roosevelt died on April 12, 1945, due to poor health and exhaustion, just three months into his term. This made Harry S. Truman the president, since he was vice president when Roosevelt died. About two weeks after Roosevelt's death, on April 24, Truman received a mysterious letter from Secretary Stimson. In the letter, Stimson referred to a "highly secret matter" that he believed Truman should be informed of as soon as possible. The next day, April 25, the men met in Truman's office with General Groves, the military director of the Manhattan Project (O'Neal 24). American development of this secret atomic bomb began in 1939, while President Roosevelt was still alive. This project was so secret that Roosevelt did not even want his vice president Harry S. Truman to know anything about it. Truman couldn't believe it until he read Secretary Stimson's memo. That night he wrote a letter in his journal about the United States developing an explosive powerful enough to destroy the world. Tr...... middle of paper ......agasaki." Center for Strategic and International Studies. Np, August 10, 2012. Web. March 16, 2014. Hiroshima-and-nagasaki>. Kross, Peter " The decision to drop the bomb." World War II, July - August 2005: p. 40. EBSCOhost Web, March 14, 2016. O'Neal, Michael. San Diego, California: Greenhaven Press, 1990. Print. Sullivan, Edward T . "Trinity and Judgment Day." The Ultimate Weapon: The Race to Develop the Atomic Bomb New York: Holiday House, 2007. 98-109. Print. .com, sd Web.. 2014. .