On This Day: US Detonates World’s First Atomic Bomb

In August 1939, Albert Einstein wrote to President Franklin D. Roosevelt advocating the exploration of nuclear fission and its potential use as a weapon. In his letter, Einstein stated that recent research made it increasingly possible “to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power … would be generated.”

Roosevelt did not want to risk a German monopoly on such a weapon and approved uranium research in October 1939. This decision was the first among many that culminated in the Manhattan Project, America’s top-secret project to develop the atomic bomb.

According to Time magazine, the project “had top priority on materiél and Army specialists. But few, if any, of the 65,000 who at one time worked on materials, handled blueprints, and expedited the job, ever knew what ‘Manhattan Project’ was.”

Less than three years after the project’s start, the world’s first atomic bomb was detonated on Alamogordo Air Base in New Mexico. “At precisely 5:30 a.m. on Monday, July 16, 1945, the nuclear age began,” declares the U.S. Department of Energy.

In a memorandum to the secretary of war, project leader Gen. Leslie Groves wrote that the detonation “was successful beyond the most optimistic expectations of anyone.”

“As to the present war,” he continued, “there was a feeling that no matter what else might happen, we now had the means to insure its speedy conclusion and save thousands of American lives. … The effects could well be called unprecedented, magnificent, beautiful, stupendous and terrifying. No man-made phenomenon of such tremendous power had ever occurred before.”

The U.S. Department of Energy recounts significant events in the Manhattan Project. The Web site links to information on the earliest atomic discoveries in the late 1800s to 1945 and the post-nuclear age.

Within a month of the test, on Aug. 6 and Aug. 9, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki, respectively. This marked the only two times a nuclear weapon has been used in combat.

President Harry S. Truman addressed the nation 16 hours after the bombing of Hiroshima. “What has been done is the greatest achievement of organized science in history,” he said.

Gen. Leslie R. Groves
After overseeing the construction of the Pentagon, Groves was appointed chief of the top-secret Manhattan Engineering District and immediately began assembling his team. According to the Los Alamos National Laboratory Web site, “His most important appointment, as well as his most controversial, was J. Robert Oppenheimer.”

J. Robert Oppenheimer
Oppenheimer was appointed scientific director of the Manhattan Project in June 1942. He oversaw the construction of the Los Alamos laboratories and helped to gather together a team of physicists to build the atomic bomb.

Oppenheimer dubbed the first detonation the “Trinity” Test, inspired by the poems of John Donne. The Atomic Archive offers a recap of the life of the “‘father’ of the atomic bomb.”