they used uranium and plutonium.
The element first used for fission in an atomic bomb is uranium.
They did steal all the information needed to make it. Read "The Making of the Atomic Bomb" by Richard Rhodes
Uranium-235 was used in the atomic bomb dropped on Hiroshima.
Uranium 235
The devastation of the Atomic Bomb was known but never thought to be needed twice. There was little known knowledge of the effects of radiation.
the atomic number of each isotope-apex;)
Truman. The war needed to be ended ASAP!
He needed to bring the end to the war.
Plutonium
I believe it was the atomic bomb. Evidence: every country in the war was researching WMD's but the atomic bomb was the most heavily researched of all.
He didn't care what the US officially informed the USSR about or not, he had spies that provided all the information about the atomic bomb he needed.
Little boy was a uranium fission bomb and Fat man was a plutonium implosion type bomb. Both required the needed research. There is no record into was harder to produce.