There are a number of errors in the photo captions, so for the record: 1. The "Little Boy" device, cylindrical in shape, was a U-235 gun-type device that was s

There are a number of errors in the photo captions, so for the record: 1. The "Little Boy" device, cylindrical in shape, was a U-235 gun-type device that was so simple in its design that it was dropped -- on Hiroshima on August 6, 1945 -- without having been tested first. The U-235 was extraordinarily expensive to produce, taking up a large percentage of the Manhattan Project budget and several years. Two independent programs using different methods were designed to produce sufficient U-235, which needs to be separated from the much more abundant and non-fissioning U-238 isotope. The expense of extracting U-235 is the reason that only one such bomb was used, and only a few were ever built. 2. The "Fat Man" bomb design used an isotope of plutonium (Pu-239) that was bred in fission reactors in Hanford, WA and Oak Ridge, TN over a relatively short time and at much lower cost. This bomb was tested at the Trinity site on July 16, 1945, in advance of its use on Nagasaki (August 9, 1945) because its implosion design was much more complex than the uranium bomb. 3. All modern fission weapons, and the trigger devices in fusion weapons, are design descendants of the Pu-239 "Fat Man" device that was dropped on nagasaki.