When Japan bombed Pearl Harbor, they basically presaged their own demise, with the United States dropping two atomic bombs on the cities of Nagasaki and Hiroshima in 1945. The two bombs caused unimaginable devastation to the cities and caused injuries and death to tens of thousands of people, making Japan surrender unconditionally. Not many of us know that there was supposed to be a third bomb that earned the moniker “demon core” because it tended to kill anyone who did not handle it with the greatest care.

Third Bomb

The Little Boy Bomb and the Fat Man Bomb, as they were called, were designed and produced in the Manhattan Project, a research and development operation during World War II. The project was headed by the United States and supported by the United Kingdom and Canada. It was Major General Leslie Groves of the US Army Corps of Engineers who oversaw the project from 1942 to 1946, while it was nuclear physicist and Los Alamos Laboratory’s Robert Oppenheimer who designed the actual bombs.

Little Boy nuclear bomb with casing open. (US Government – Manhattan Project, Public domain, via Wikimedia Commons)

The Manhattan Project started in 1939 with 130,000 people and about 2 billion USD cost, a huge chunk of which was for building factories to produce fissile material from uranium and plutonium, which were hard to produce at that time. The research and production took place in over thirty sites across the US, United Kingdom, and Canada, so it would be unbelievable to think that the plan was to create only two atomic bombs. And it indeed was incorrect.

The Atomic bomb project consumed 25% of the US defense budget in WWII and remains the most expensive weapons system ever developed in history.  In terms of man-hours and money, it was the equivalent of undertaking the 20-year Panama Canal project, building it in a single year, and doing it four times

By the summer of 1945, the Manhattan Project had produced enough fuel to create three bombs and a fourth one on the way. The fuel was used for the Trinity test and the two bombs.

Dropping the Two

The United States dropped the two atomic bombs over the two Japanese cities. The first was in Hiroshima on August 6, 1945. On August 9, Enola Gay was supposed to drop the second bomb on Kokura, but the cloudy skies made it impossible to see the target, so they headed over to their secondary target and bombed Nagasaki instead.

Atomic Cloud Over Nagasaki, 1945. (pingnews.com, Public domain, via Wikimedia Commons)

In the only use of nuclear weapons in armed conflict, about 129,000 to 226,000 people were killed. When Japan did not immediately surrender, the United States was ready to drop its third nuclear bomb on August 19. Japan announced its surrender just three days before.

The Demon Core

Because of Japan’s surrender, the US was left with a 6.2 kg, 9 cm wide plutonium core that should’ve been for the third bomb that they decided to use for testing.

From 1945 to 1946, the core was used for experiments, although its super slim safety margin made it supercritical. One of the experiments done on the core was partially surrounding it with neutron reflectors that reflected neutrons from the nuclear fission reaction and then back into the core. The process even increased the reaction. The surrounding neutron reflectors would cause the core to rapidly enter criticality, which would release a fatal and powerful flash of radiation.