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SciTech Tuesday: 70th Anniversary of the bombing of Hiroshima and Nagasaki

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On August 6, 1945, the Enola Gay dropped the bomb named ‘Little Boy’ on Hiroshima. On August 9, the Bockscar dropped ‘Fat Man’ on Nagasaki. ‘Little Boy’ was a uranium bomb, and ‘Fat Man’ was made with plutonium. Years of work to build the bombs and overcome technical difficulties in development and deployment had proceeded these missions. It was difficult, because of the amount of destruction, to quantify the casualties accurately, but estimates are about 140,000 in Hiroshima and 70,000 in Nagasaki.

There have been many articles in the news recently, because of this 70th anniversary, and several prior SciTech Tuesday posts have discussed the Manhattan Project.

In this post I will focus on a few interesting points about the events surrounding the two bombings:

–When the first atomic test was made at Trinity, on July 16, ‘Little Boy’ was already aboard the USS Indianapolis on its way to Tinian. The test at Trinity was of a plutonium bomb like ‘Fat Man,’ so ‘Little Boy’ was the first detonation of a uranium bomb.

–Several B-29s had crashed and burned on the Tinian runway in the week before the Enola Gay was to carry its payload to Japan. As a precaution ‘Little Boy’ was not armed until the plane was in the air. On a B-29 crawling into the bomb bay and rewiring a bomb is not a trivial matter.

–Both ‘Little Boy’ (9700 lbs) and ‘Fat Man’ (10,800 lbs) were so heavy that they had their planes well overloaded.

–While the materials to assemble ‘Little Boy’ were carried by sea on the USS Indianapolis, the materials to assemble ‘Fat Man’ were transported by air in a C-54. There was spare plutonium in case a plane went down, but there was no extra uranium.

–Kokura escaped bombing twice. It was the backup target for the August 6 run, and the primary target for the August 9 run. On August 9 the weather report said there was too much smoke from a recent firebombing of a neighboring city for a visual target. The operational plans required visual targeting.

–The first bombing mission went off with no logistical problems. The Enola Gay left Tinian on time, met its companion planes on time, encountered no resistance, and missed the target by only about 100 feet. The second bombing mission had many problems. Its date had been moved up because of a series of bad storms predicted for the next week, but the Bockscar left late because of mechanical problems, and missed its rendezvous with some of its companions. With Kokura obscured by clouds and smoke, the Bockscar flew to Nagasaki and dropped the bomb, but missed its target, thus limiting the casualties from the bomb. The plane was critically low on fuel and had to make an emergency landing at Okinawa. The pilots had to spin the plane around to keep it from running off the end of the short runway there.

–After the bombings scientists involved in the Manhattan Project were split in their reactions. Some, like Robert Oppenheimer, Niels Bohr, and Linus Pauling, were moved to work against further use and development of nuclear weapons. Others continued to work in weapons development. Many were concerned about the results of unilateral power, and wanted to disseminate knowledge of the technology widely. It turned out that Soviets had spies in the Manhattan Project, and were able to launch their own nuclear weapons program beginning in 1945.

Posted by Rob Wallace, STEM Education Coordinator at The National WWII Museum.


all images from the collection of The National WWII Museum

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