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July 16, 1945

The first atomic bomb test, near Alamogordo, New Mexico, July 16, 1945. Jack Aeby/Los Alamos National Laboratory.

First Atomic Bomb Test in New Mexico

Be sure to watch our webinar recorded on 7/13/2020

Two types of atomic bombs were developed during the war (see some explanation in 11 June entry). A relatively simple gun-type fission weapon was made using uranium-235, an isotope that makes up only 0.7 percent of natural uranium. Since it is chemically identical to the most common isotope, uranium-238, and has almost the same mass, it proved difficult to separate.

Three methods were employed for uranium enrichment: electromagnetic, gaseous and thermal. Most of this work was performed at the Oak Ridge, Tennessee facility. In parallel with the work on uranium was an effort to produce plutonium Pu-239. Plutonium does not occur naturally in mineable quantities like uranium does. Nuclear reactors were constructed at Oak Ridge and Hanford, Washington, in which uranium was irradiated with neutrons and transmuted into plutonium. The plutonium was then chemically separated from the uranium. The gun-type bomb design proved impractical to use with plutonium so a more complex implosion-type nuclear weapon was developed in a concerted design and construction effort at the Manhattan Project's principal research and design laboratory in Los Alamos, New Mexico.

Because the complete detonation of a kilogram of plutonium, (Pu-239), produces an explosion equivalent to over 10,000 tonnes of chemical explosive, the bomb designers wanted to make bombs with Pu-239 instead of U-235 so they could be made smaller for the same destructive effect. The bomb designers were sufficiently unsure about the functioning of the Pu-239 bomb design they arranged that one be tested in the desert of New Mexico at the Alamogordo Bombing and Gunnery Range  in the geographic feature called the Tularosa Basin on 16th July 1945. This most-secret test was code-named “Trinity” and it was the first, but unfortunately not the last, time an atomic bomb was exploded.

The 21 kiloton explosion occurred on a tower 100 feet from the ground and has been likened to a “dirty bomb” that cast large amounts of heavily contaminated soil and debris—containing 80 percent of the bomb’s plutonium—over thousands of square-miles. (See Figure 1. below)


After a nearly half a century of denial, the US Department of Energy concluded in 2006, “… the Trinity test also posed the most significant hazard of the entire Manhattan Project.” Four years later the US Centers for Disease Control gave weight to this assessment by concluding: “New Mexico residents were neither warned before the 1945 Trinity blast, informed of health hazards afterward, nor evacuated before, during, or after the test. Exposure rates in public areas from the world’s first nuclear explosion were measured at levels 10,000- times higher than currently allowed.”

But the people downwind of the 1945 explosion in New Mexico have been denied official recognition, even though the Trinity shot was considered one of the dirtiest of American nuclear tests, with a significant absence of safeguards to protect people from dense radioactive fallout. Safety took a back seat to making sure the first atomic bombs would meet their enormously destructive potential.

Several years ago, residents of central and southern New Mexico organized to fight for compensation. Known as the Tularosa Basin Downwinders, they have made a compelling case that cancers and other diseases are due to the Trinity blast and subsequent radioactive fallout from open air atomic bomb tests in Nevada. Please consult the timeline to find the webinar we will be holding in July 2020 with speakers from the NM Tularosa Basin Downwinders Consortium, who will inform us about this ongoing problem.

On the morning of 22 July 1945, during the Potsdam Conference of the Big 3 (see timeline entry on 17 July), British Prime Minister, Sir Winston Churchill, was given a full account of this first atom bomb test in New Mexico. Inside a one-mile circle, devastation had been total. Churchill then went to see President Truman. “Up to this moment,” Churchill recalled, “we had shaped our ideas towards an assault upon the homeland of Japan by terrific air bombing and by the invasion of very large armies. We had contemplated the desperate resistance of the Japanese fighting to the death with Samurai devotion, not only in pitched battles, but in every cave and dug-out. To overcome Japanese resistance ‘man by man’ and conquer Japan ‘yard by yard’ might require the loss of a million American soldiers and half a million British—or more if we could get them there: for we were resolved to share the agony.”

With the news that the atomic bomb was a reality, Churchill reflected, “all this nightmare picture had vanished. In its place was the vision—fine and bright indeed it seemed—of the end of the whole war in one or two violent shocks.”

Further reading:

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