top of page

Who Was Oppenheimer And What Was The Manhattan Project? – A Quick And Easy Guide

Updated: Aug 21, 2023

J. Robert Oppenheimer director of the Manhattan Project World War 2
A portrait of J. Robert Oppenheimer from the Los Alamos National Laboratory.

Who Was Oppenheimer?

J. Robert Oppenheimer was an American scientist who specialised in a branch of physics called theoretical physics. A theoretical physicist like Oppenheimer would spend their time coming up with mathematical explanations for natural events.

Where Did He Learn About Science?

As you can imagine, Oppenheimer was a very intelligent man. In fact he studied at three of the top universities in the world, including Harvard University in the USA, Cambridge University in the UK and the University of Göttingen in Germany. He had the opportunity to study with some of the greatest scientific minds of his time and published many scientific papers that became very famous.

What Was Oppenheimer Best Known For?

Though Oppenheimer was an amazing scientist, he is probably best known for his association with the Manhattan Project, where he established himself as the “father of the atomic bomb”.

A pin showing the Manhattan Project's emblem
A pin showing the Manhattan Project's emblem

What Was The Manhattan Project?

During the Second World War, the Allied countries became more and more afraid of what would happen if Nazi Germany built an atomic bomb. Because of this, there was a race to build a bomb before Germany could.

And so a top-secret government weapons program was formed, known as the Manhattan Project. American President Franklin D Roosevelt approved the project just two months before the USA joined the Second World War on the Allied side in 1941. The aim of the project was to use nuclear fission to make the ultimate destructive weapon; the biggest and most powerful bomb the world had ever seen.

What Did Oppenheimer Do For The Manhattan Project?

Oppenheimer was the head of the secret weapons laboratory for the Manhattan Project. He chose a location in Los Alamos, New Mexico as the best place to set up his lab. Here, scientists focused on designing, building and testing bombs. Although there were just a few people to begin with, by 1945 Oppenheimer’s lab had over 6,000 scientists toiling away on the project.

The Trinity test of atomic bomb Manhattan Project Oppenheimer
A colour picture of the Trinity test - the first detonation of a nuclear bomb in the world.

What Kind Of Bombs Did They Make?

The scientists at Los Alamos successfully made two different types of bombs. One was made out of Uranium and one was made out of plutonium. The bombs were nicknamed “Little Boy” and “Fat Man”.

How Did They Know The Bombs Would Work?

A test of the plutonium bomb was scheduled to take place on 16th July 1945 in Alamogordo, New Mexico. The test was nicknamed Trinity and everybody was nervous about it. Nobody quite knew what was going to happen. One physicist even joked that the bomb would destroy all life on planet Earth.

What Happened At The Trinity Test?

Trinity was detonated at 5:29am and what followed was the biggest man-made explosion the world had ever seen. Oppenheimer later remembered the reaction of the people that witnessed the blast:

“We knew the world would not be the same. A few people laughed, a few people cried. Most people were silent.”

A quote came to Oppenheimer’s mind from the Hindu scripture, the Bhagavad Gita. He supposed everyone must have been thinking of that quote that day:

“I am become Death, the destroyer of worlds.”

Oppenheimer visits Trinity ground zero Manhattan project
Oppenheimer (left) visits Ground Zero, the spot where the Trinity test bomb was detonated. Credit: Digital Photo Archive, Department of Energy (DOE), courtesy of AIP Emilio Segrè Visual Archives

Did They Ever Use The Bombs For Real?

At first, Oppenheimer expressed disappointment that they hadn’t managed to make the bomb in time to be used against Nazi Germany (Germany had surrendered in the war just a month before the Trinity test). But Oppenheimer soon changed his mind when he saw the level of destruction caused when the bombs were actually used as weapons against real people.

The bomb was first used on Hiroshima on 6th August 1945 and then on Nagasaki on 9th August 1945. In total, over 100,000 people died in the initial explosions, then many, many more died from their injuries and the effects of the weapons in the days, weeks and years to come. To this day, the bombings of Hiroshima and Nagasaki remain the only time that nuclear weapons have been used in armed conflict worldwide.

What Happened To Oppenheimer?

In October 1945, Oppenheimer visited US President Harry Truman and expressed his disappointment at the second use of the bomb, on Nagasaki, claiming he felt he had “blood on his hands”.

In 1947, after the war, Oppenheimer became chairman of the General Advisory Committee of the Atomic Energy Commission. In his role, he was very loudly against the idea of the government developing an even more powerful bomb, the hydrogen bomb. This led to him being stripped of his security clearance, bringing an end to his job as a government scientist in 1954.

Oppenheimer Manhatten Project Trinity test nuclear bomb test site ground zero
Oppenheimer (centre left with the light hat and his foot on the mound) visits Ground Zero at the site where the Trinity test nuclear bomb was detonated.

Image Credit line: Unless otherwise indicated, this information has been authored by an employee or employees of the Los Alamos National Security, LLC (LANS), operator of the Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396 with the U.S. Department of Energy. The U.S. Government has rights to use, reproduce, and distribute this information. The public may copy and use this information without charge, provided that this Notice and any statement of authorship are reproduced on all copies. Neither the Government nor LANS makes any warranty, express or implied, or assumes any liability or responsibility for the use of this information.

Related Posts

See All


bottom of page