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The Manhattan Project was one of the most secretive and world-changing scientific efforts of the 20th Century.

The discovery of nuclear fission

The Manhattan Project began in 1942, during the height of World War II, as a response to the alarming possibility that Nazi Germany might develop a nuclear bomb. After the 1938 discovery of nuclear fission by scientists in Berlin, physicists realized that splitting atoms — especially isotopes of uranium and plutonium — could release enormous amounts of energy.

The start of the Manhattan Project

Concerned about this potential, physicist Leo Szilard drafted a letter, which Albert Einstein signed, urging U.S. President Franklin D. Roosevelt to investigate uranium’s military uses. Roosevelt responded by creating a series of research committees, which evolved into the Manhattan Project. The initiative was led by General Leslie Groves and physicist J. Robert Oppenheimer, who directed a secret lab at Los Alamos, New Mexico.

Key locations in the project

More than 130,000 people contributed to the project, including major figures like Klaus Fuchs, later revealed to be a Soviet spy, and Leona Woods, the youngest and only woman involved in building the first nuclear reactor. Research was carried out across the U.S. — uranium was enriched at Oak Ridge, Tennessee, and plutonium was produced in Hanford, Washington.

The first bomb test and its impact

On July 16, 1945, the first successful test of a plutonium bomb — code-named “Trinity” — took place in the Jornada del Muerto desert of New Mexico. A brilliant flash lit up the sky, followed by a mushroom cloud that soared over 7 miles high. Witnesses felt a blast of heat like an oven. Reflecting on the event, Oppenheimer quoted a line from Hindu scripture: “Now I am become Death, the destroyer of worlds.”

The bombings of Hiroshima and Nagasaki

The bomb’s power was demonstrated just weeks later. On August 6, 1945, a uranium bomb called “Little Boy” was dropped on Hiroshima, Japan. It exploded 1,900 feet in the air, killing approximately 70,000 people immediately. A second bomb, “Fat Man,” made of plutonium, was dropped on Nagasaki on August 9, killing up to 80,000 people. Japan surrendered on August 15, and World War II officially ended on September 2.

The aftermath and ongoing debates

The use of atomic bombs ushered in the Cold War and a global nuclear arms race. The U.S. and the Soviet Union built up arsenals under the doctrine of mutual assured destruction (MAD). Nearly 80 years later, debate continues over whether the bombings were justified and how to prevent future nuclear conflict.

© Danny Bird / www.historyextra.com