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Explained: How the US’ Trinity Test led to the dawn of the atomic age

On this day, exactly 75 years ago, scientists tested Gadget — the world’s first atomic bomb — in what was dubbed as the ‘Trinity Test’. Less than a month later, an identical nuclear bomb called ‘Fat Man’ was dropped on the Japanese city of Nagasaki, killing tens of thousands of people.

By: Explained Desk |
Updated: July 17, 2020 12:21:30 am
US nuclear test, US Gadget Bomb, The Manhattan project, Manhatattan project US, US Atomic Bomb test, Express Explained The super bomb, nicknamed ‘Gadget’, was built by a team of scientists at a top-secret site in Los Alamos, New Mexico. (Source: Wikimedia Commons)

At precisely 5.30 am on July 16, 1945, the world’s first super bomb — loaded with about 13 pounds of plutonium at its core — exploded in a desert in New Mexico, destroying everything in its vicinity and melting vast swathes of sand into sea-green glass.

Minutes later, hundreds of US scientists and military personnel — who had taken cover at bunkers located around 10,000 yards away from the bomb — celebrated the dawn of the nuclear age. Before it detonated, the scientists had placed bets on what could happen. Some believed that the bomb would be a dud and would fail to explode. Others feared a far deadlier consequence — the end of the world.

The super bomb, nicknamed ‘Gadget’, was built by a team of scientists at a top-secret site in Los Alamos, New Mexico. It was developed as part of the US-led Manhattan Project, which sought to build nuclear weapons to give the allied forces an edge over Germany, Japan and Italy in World War 2.

On this day, exactly 75 years ago, the scientists tested Gadget — the world’s first atomic bomb — in what was dubbed the ‘Trinity Test’. Less than a month later, an identical nuclear bomb called ‘Fat Man’ was dropped on the Japanese city of Nagasaki, killing tens of thousands.

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What was the Manhattan Project?

Merely a month after Germany initiated World War II by invading Poland, a letter signed by Nobel prize-winning physicist Albert Einstein warned then-US President Franklin D Roosevelt of the potential threat posed by an atomic weapon being developed by Adolf Hitler.

Soon after, the United States launched a secret atomic research undertaking, code-named the Manhattan Project, which sought to develop an atomic weapon to end the war. The project brought together some of the country’s leading atomic experts as well as exiled scientists and physicists from Germany and other Nazi-occupied nations.

However, the Manhattan Project remained a relatively small-scale initiative for the next two years. It was only after the bombing of Pearl Harbour by the Japanese Navy Air Service in 1941, when President Roosevelt declared that the US would enter the Second World War, that the project was officially kicked into gear.


US Army Colonel Leslie R Groves was appointed to lead the project. By December, 1942 facilities were established in remote locations across the US, as well as in Canada. However, the super bomb was finally designed and conceptualised by a team of scientists at a top-secret laboratory in Los Alamos.

The team at Los Alamos was headed by J Robert Oppenheimer, a physics professor at the University of California, Berkeley. Oppenheimer later came to be known as the “father of the atomic bomb”. His team included Danish scientist Niels Bohr, Italian scientists Enrico Fermi and Emilio Segré, Hungarians Edward Teller and John von Neumann, Hans A. Bethe from Germany, as well as American-born scientist Richard Feyman.

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The Los Alamos team developed two types of bombs — one was uranium based, which was later code-named ‘the Little Boy’ before it was dropped on Hiroshima; the other had a plutonium core. Testing the ‘Little Boy’ was not feasible, as there was not enough uranium available. The Plutonium bomb was eventually tested at the Trinity site on July 16, 1945.

What happened during the Trinity Test?

A few days prior to the test, parts of the dismantled super bomb were carried to the Alamagordo Bombing Range, which was located around 337 km away from Los Alamos. An army sedan first brought the bomb’s plutonium core to the site on July 12. The next day, Gadget’s non-nuclear components were brought to the range. By July 15, the bomb was assembled and placed on top of a 100-foot firing tower.

A Mushroom cloud of ‘Gadget’ over Trinity, seconds after detonation. (Source: Wikimedia Commons)

In the evening, the team of scientists and military personnel arrived at the test site, where it was pouring rain. The scientists feared that they would not be able to carry out the test at 4 am, the next morning, as planned. As tensions rose, the scientists began placing their bets, a report by the US’ Office of Scientific and Technical Information (OSTI) claimed. Oppenheimer bet ten dollars that the bomb would not work.

The test was eventually rescheduled to 5.30 am. Early the next morning, the skies cleared just in time for the test. The Los Alamos team retreated and took cover at bunkers, located about 10,000 yards away from the bomb in all four directions. The scientists ensured that they were all located in different bunkers, in case of an accident. If tragedy struck, they wanted to make sure that someone was left behind to further the research.

At exactly 5.30 am, the bomb went off leaving a mammoth mushroom of smoke and gas in its wake. The firing tower, much like everything else in the area, was destroyed completely. The device exploded with a power equivalent to 21,000 tons of TNT, the New York Times reported.


In an interview with NBC in 1965, Oppenheimer said that a line from the Bhagavad Gita occurred to him at the time of the explosion — “Now I am become death, the destroyer of worlds.”

After celebrating the success of the test, Colonel Leslie Groves and Oppenheimer began drafting their report to submit to the Secretary of War and the US President.


What were the repercussions of the Trinity Test?

New Mexico residents were pointedly not warned before the test, to ensure that it was carried out secretly. Data collected by the New Mexico health department, which showed the adverse impact of radiation caused by the detonation, was ignored for years after the test.

A sudden rise in infant mortality was reported in the months after the explosion, according to a study published by the Centrers for Disease Control and Prevention. Several residents also complained that the number of cancer patients went up after the Trinity Test.


It was only in 1990, when the federal government passed the Radiation Exposure Compensation Act (RECA), that residents of North Mexico who contracted Cancer and other other illnesses due to radiation exposure received compensation.

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The dust outfall from the explosion was expected to have travelled nearly 100 miles from the test site, posing a serious threat to residents in the area. Many families complained that their livestock suffered skin burns, bleeding and loss of hair.

There is more data available on the damage done by the atomic bombs in Japan. The Hiroshima and Nagasaki bombings are known to have killed well over 200,000 people — many of whom succumbed to radiation poisoning in the weeks after the blasts.

The uranium bomb in Hiroshima on August 6, 1945, destroyed around 70 per cent of all buildings and caused around 140,000 deaths by the end of 1945. The plutonium bomb explosion over Nagasaki, which took place three days later, killed 74,000 people that year, according to International Campaign to Abolish Nuclear Weapons (ICANW) data.

After seeing the destruction caused to the two Japanese cities, Oppenheimer publicly admitted that he regretted building a bomb that could cause an apocalypse. “Mr. President, I feel I have blood on my hands,” he famously told US President Harry Truman later that year.

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How many countries worldwide now have nuclear weapons?

Seventy-five years after the Trinity Test, as many as nine countries around the world are currently in possession of nuclear weapons. These include, the US, the UK, Russia, France, India, China, Israel, Pakistan and North Korea.

At least eight countries have detonated over 2,000 nuclear test explosions since 1945, according to data released by

The most recent instance of nuclear bomb test explosions conducted by India, were the series of five explosions done as part of the Pokhran-II tests in May 1998. The first test, code-named Smiling Buddha, took place in May 1974.

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First published on: 16-07-2020 at 04:54:44 pm
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