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

Written By Jordan Jordan
Last updated: February 27, 2023

July 16, 2011 06:00 AM

by Jordan Termine

On July 16, 1945, the Manhattan Project conducted the Trinity Test in New Mexico, the first atomic bomb detonation in history and the dawn of the Atomic Era.

Trinity Test Successful

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. “Hoisted atop a 150-foot tower, the plutonium device, or Gadget, detonated at precisely 5:30 a.m. over the New Mexico desert, releasing 18.6 kilotons of power, instantly vaporizing the tower and turning the surrounding asphalt into green sand,” describes the the U.S. Department of Energy. “Seconds after the explosion came an enormous blast, sending searing heat across the desert and knocking observers to the ground.”

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 ensure 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 Bombing of Hiroshima and Nagasaki

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 had 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.

The findingDulcinea Web Guide to World War II links to the most comprehensive and reliable sources on the war.

Key Players: Gen. Leslie Groves; J. Robert Oppenheimer

Sources in this Story

  • The Atomic Heritage Foundation: Einstein’s Letter to Franklin D. Roosevelt
  • Time: Birth of an Era
  • U.S. Department of Energy: The Trinity Site
  • PBS: General Leslie Groves’ Memorandum Describing the First Nuclear Test In New Mexico
  • Los Alamos National Laboratory: General Leslie R. Groves
  • Atomic Archive: J. Robert Oppenheimer (1904-1967)

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.”

Charles Eames

Jordan joined the findingDulcinea team in May 2008. Prior to that he worked as an intern for the Obama campaign in New Hampshire. He is currently pursuing a B.A. in economics and government at Bowdoin College.

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