Ben’s Blog

A few weeks ago, I read virtually everything Wikipedia has on the development of the nuclear weapons used on Hiroshima and Nagasaki. I hadn’t planned on writing a blog post on this topic, but something interesting came up yesterday that I did want to post about and this seemed like a good introduction. It wasn’t until I after I had decided to write this post that I realized today was the 65th anniversary of the bomb being dropped on Hiroshima.

Numerous books have been written about the Manhattan Project, so I won’t even attempt an outline here, but below are the main Wikipedia articles for your reference:

• Manhattan Project
• Trinity
• Atomic bombings of Hiroshima and Nagasaki
• Debate over the atomic bombings of Hiroshima and Nagasaki
• Surrender of Japan

Read these and some of the links on these pages and you’ll know a lot about the bombs, their development, why they were used, etc. Below are a few of the facts that were new to me or that I find particularly interesting. I’m sure there were more, but I didn’t take notes.

One of the things that makes the Manhattan Project so interesting is that these scientists took a completely theoretical idea and made a working weapon in less than four years (12/1941 – 8/1945). Granted, they did have virtually limitless resources and some of the brightest minds of their time.

In my opinion, the single most interesting person involved in the project was Robert Oppenheimer, the scientific director. He famously lost his security clearance in 1954 for having ties to Communism. History has cleared his name regarding any spying. It is now known that the KGB tried to recruit him numerous times, but they were always turned down.

The project actually produced two different types of nuclear weapons: one based on Uranium-235 and another on Plutonium-239. The element Plutonium had only been discovered in February, 1941.

The Uranium-235 was produced in Oak Ridge, Tennessee. The site was picked, in part, due to the availability of cheap hydroelectric power from TVA. At one time, the site used over a sixth of the electrical power produced in the United States. Due to security concerns, the Governor of Tennessee did not know Oak Ridge existed for some time, even though it would soon become the fifth largest city in Tennessee. Perhaps unsurprisingly, the area of the Oak Ridge complex where the Uranium was enriched is now an EPA Superfund site.

Copper was in short supply during World War II, so Oak Ridge was loaned 14,700 tons  of coinage silver (currently worth $7.3 billion) from the US Treasury to create massive electromagnetic coils. Approximately 99.965% of it was returned to the Treasury after the war.

Due to the small amount of Uranium-235 available and the confidence of the scientists, a test was never carried out using the Uranium design. They didn’t know for certain it would work until it was dropped on Hiroshima. As an engineer, I’m astounded that they pulled this off in such a short time with no final test.

On July 16th, 1945, a Plutonium weapon was tested at the White Sands Proving Ground in New Mexico. The test was code-named Trinity. The explosion was heard 200 miles away. The Army put out a press release explaining that a remote ammunitions magazine had exploded. Near the explosion, the sand was turned to a light green, radioactive glass that came to be called Trinitite.

In the brainstorming stage of target selection, Kyoto was a favorite. Supposedly Kyoto was taken off the list by Secretary of War Henry Stimson who had honeymooned there.

On July 26th, 1945, the Potsdam Declaration was released, in which the Allies requested an unconditional surrender from Japan. It promised “prompt and utter destruction” if they did not surrender. The Japanese did not respond.

On August 6th, 1945, three B-29s left Tinian headed toward Hiroshima by way of Iwo Jima, a six hour flight. They were picked up by the Japanese on radar, and the alert was initially raised, but after determining there were only three planes, the air raid sirens were turned off. The Japanese had previously decided not to intercept small formations with fighters to conserve fuel and planes, which is what happened on August 6th. When the planes arrived at Hiroshima it was clear. Had it been cloudy, they would have diverted to Kokura.

“Little Boy” was dropped from the Enola Gay at 8:15 local time. It detonated 1900 feet above the city, as designed. Approximately 70,000 people (~30% of Hiroshima’s population) died immediately. It is estimated that up to a total of 200,000 people died by 1950 due to effects from the bomb.

On August 8th, the Soviet Union finally declared war on Japan and invaded Manchuria.  Japan had been hoping to avoid war with the Soviets. They still did not surrender.

On August 9th, Bockscar and its supporting B-29s headed for Kokura. They had orders to drop the bomb only if they could see their target. Weather scouting planes flying an hour ahead reported clear skies. Bockscar was delayed due to a supporting plane missing its rendezvous. By the time it arrived in Kokura, it was cloudy. They diverted to the secondary target, Nagasaki.

At 11:01 local time, “Fat Man,” a Plutonium bomb similar in design to the one tested previously, was dropped on Nagasaki. Between 40,000 and 70,000 people died immediately.

At this point the officials in Japan were still split on the issue of surrender. Early on August 10th the Emperor himself came out in favor surrender, as long as he could retain his power. The Allies continued to demand an unconditional surrender. Finally, on August 14th, the Emperor and his government agreed. The was an unsuccessful coup d’état by elements of the military that did not want to surrender.

The US planned to have another nuclear weapon ready by August 17th, and it would have most likely been used had Japan not surrendered.

There is, of course, a debate about whether or not nuclear weapons should have been used on Japan. I have my opinion. I encourage you read up on the facts and develop your own.

If you know of any related, interesting facts that I missed, please post them in the comments.