The US Government called on Dr. Kistiakowsky to help solve the problem with the new weapon the physicists at Los Alamos had been struggling for some time already with – they could not create an implosion capable of igniting the atomic bomb’s plutonium core. George Kistiakowsky joined the Manhattan Project in 1944, replacing Seth Neddermeyer as head of the Explosives (“X”) Division for the National Defense Research Committee responsible for the explosive components of fission weapons. It is under his leadership that complex explosive lenses capable to compress the plutonium sphere to achieve critical mass were developed.
The implosives was the only real hope for the Trinity Device to work, but it was so hard to make, that at one time Robert Oppenheimer considered resigning his directorship because of it. Kistiakowsky recalled: “So much pessimism was developing about our ability to build satisfactory lenses, that Captain Parsons began urging (and he was not alone in this) that we give up lenses completely and try somehow to patch up non-lens type of implosion.”
Kistiakowsky introduced the most dramatic innovation of finishing the high-explosive castings by machining them – In February 1945, Kistiakowsky chose an explosive called Composition B to serve as the fast-burning component of Fat Man’s lenses. It had to be poured as a hot slurry of wax, molten TNT, and other components and then cooled in certain ways to avoid air bubbles inside the large castings fifty pounds and more each. “The explosive was poured in and then people sat over that damned thing watching it as if it was an egg being hatched, changing the temperature of the water running through the various cooling tubes built into the mold.” Because of Kistiakowsky’s precision approach, there was not a single explosive accident in over 50,000 machining operations on those castings.