In 1945, captured German scientists were secretly recorded discussing the recent American bombing of Hiroshima:
WEIZSÄCKER: History will record that the Americans and the English made a bomb, and that at the same time the Germans, under the HITLER regime, produced a workable engine. In other words, the peaceful development of the uranium engine was made in GERMANY under the HITLER regime, whereas the Americans and the English developed this ghastly weapon of war.
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7. In a conversation between WIRTZ, VON WEIZSÄCKER and HEISENBERG,HEISENBERG repeated that in July 1944 a senior SS official had come to him and asked him whether he seriously believed that the Americans could produce an atomic bomb. He said he had told him that in his opinion it was absolutely possible as the Americans could work much better and quicker than they could. VON WEIZSÄCKER again expressed horror at the use of the weapon and HEISENBERG replied that had they produced and dropped such a bomb they would certainly have been executed as War Criminals having made the “most devilish thing imaginable”.
You can download the 12-page transcript in PDF form HERE.