The Chain Reaction of a Bomb

Parsons Group was developing two bomb models by March 1944 and he wanted to test these with B-29s. Thin Man, named after President Roosevelt, used the plutonium gun design, so firing a plug of plutonium into purified plutonium. Fat Man, which was named after Winston Churchill, had an implosion method that needed a larger form factor. And then you had a smaller Little Boy, which was using a uranium gun,. The plutonium gun was eventually abandoned because it turned out that plutonium could pick up neutron 239 and increase the chances of predetination.