The Little Boy atom bomb to be dropped on Hiroshima was a "gun type" uranium bomb. Two different sized masses of fissile material were separated—one at each end. An HE charge blew a uranium “bullet” (which was actually the larger mass) down an ordnance barrel to impact against the smaller mass. Basically, two pieces of uranium were being slammed together to go supercritical. It weighed 9700 lbs. (4400 kg). It carried 140 lbs (64 kg) of fissile material. Its yield was 15 kilotons.
The Fat Man bomb to be dropped on Nagasaki was an implosive type bomb that used a combination of plutonium and uranium. It worked the same as the Gadget. The Fat Man weighed 10,300 lbs (4670 kg). It carried only 14 lbs (6.2 kg) of plutonium. Its yield was 20 kilotons.
The original physicists who worked on the Bomb did so because of the threat that Hitler might beat them to it. What they didn’t know and could not have known was something revealed in memos released back in the 1990s. According to these memos, Germany was never the intended target—Japan was. Why? Because Germany was land-locked for the most part. If a bomb was dropped on Berlin, for example, and it failed to go off then the United States had just handed the Nazis a nuclear bomb. Japan, being an island group, was different. The bombs weren’t dropped directly over the land but actually off the coast a ways. That way, if the first bomb fell into the water, it would take the Japanese some time to locate and retrieve it. This would give the US time to drop the second bomb.
That was the reason two bombs were built with a different arming system. If one bomb didn’t go off, they still had a chance to try it again. The simpler bomb, the Little Boy, was dropped first because it had the best chance of working. But it was too simple to be of much use in future wars. The much more complex system of the Fat Man was where the future of atomic weapons would be going but it might fail to detonate. The trouble is, even if the first bomb detonates, the second still had to be dropped. Because both were so hastily made, neither bomb could be stored indefinitely but would eventually become lethal with no secure place to store them. Both were made to be used immediately and a great deal of money was expended for the purpose and so both had to be used.
With the death of Roosevelt, the people in Truman’s circle impressed upon Truman that the bomb was a great new super-weapon that would give the US great leverage over the Soviets. But the bomb had to be dropped over real cities that were densely populated because that is what they were developed to do—destroy entire cities in a flash. Tests were all well and good but there was only one way to prove to the world that they really worked as advertised.
Germany was finished and was ready to surrender. They did not have the Bomb. There would be no need to drop it on them as they were an undesirable target. Japan was also beaten and would surrender in a matter of months—maybe two or three. But it was the perfect target and the bombs had to be dropped before Japan issued a formal surrender. There can be no doubt that this is true because the bombings of Hiroshima and Nagasaki occurred only some three weeks after the Trinity blast. Why such a reckless rush that could easily have proven much more catastrophic than it already was? Surely such powerful and lethal weapons should be tested more extensively. Because if the United States waited too long, Japan would surrender and then there would be no way to justify bombing them and the world (read as the Soviet Union) would not see this great demonstration of US military superiority.
Hiroshima, Japan—0815 hours (JST), August 6, 1945. Little Boy fell for 44.4 seconds before exploding at an elevation of about 2000 ft (600 m). When Einstein was informed of the dropping of this bomb, he exclaimed, “Woe is me!”
Leaflet of the Hiroshima mushroom cloud which were dropped over other areas of Japan prior to the Nagasaki destruction. The Japanese text reads:
“This photo shows the destructive power of the atomic bomb that was dropped on Hiroshima. This photo was taken from a B-29 in the air after the atomic bomb was dropped on Hiroshima on August 6. The atomic bomb’s horrendous destructive power can be understood by viewing this photo. As you see, this atomic bomb blast extended to a radius of 8 km, and the height of the bomb cloud reached about 14,000 m into the sky. The Japanese government said that Hiroshima was completely destroyed by the atomic bomb.”
Nagasaki, Japan—1102 hours (JST), August 9, 1945. The Fat Man fell incinerating 40,000 people in a flash.
"The atomic bomb made the prospect of future war unendurable. It has led us up those last few steps to the mountain pass; and beyond there is a different country." --J. Robert Oppenheimer
Crew of the Enola Gay, the B-29 that dropped the bomb on Hiroshima.
http://www.youtube.com/watch?v=tMNI25Tg4iY
I wonder which is worse; to find yourself suddenly hideously burned or growing up never being able to remember when you weren't hideously burned.