That is what physicist Kenneth Bainbridge said to Robert Oppenheimer head ofthe Manhattan Project after the Trinity test was successful on 16 July 1945. Today is the anniversary of the dropping of an atomic weapon on Hiroshima, three weeks after the test in the New Mexico desert apply named Journada del Muertes. "Little Boy" wiped out 80,000 Japanese at a stroke. Historians have debated the reasons for America's resort to nuclear weaponry against a realistically defeated enemy ever since. The reasons are several and not just the self-righteous assertion that the bomb spared American lives in an invasion of Japan's homeland.
The bomb did make an invasion unnecessary; it was sure to be bloody for both sides as bitter peripheral battles demonstrated. After the second nuclear strike against Nagasaki, The Emperor ordered the Japanese people to lay down their arms. Contrary to American war policy of "unconditional surrender", he remains on the throne to this day because General MacArthur, our own demigod, wanted a compliant civilian population during the Occupation. Dropping the bomb was a geopolitical decision as much as a tactical one. Stalin knew of the bomb's development because he had spies inside the Project. He was unmoved by Truman's announcement at Potsdam that America possessed a terrible new weapon of war. Stalin agreed to invade Manchuria, and the Red Army destroyed a major portion of the Imperial Army. Japan was completely blockaded by the US Navy. It's navy was practically destroyed. Conventional bombing raids without effective opposition in the air were consuming great swaths of Japan's cities. More Japanese were killed in fire raids on Tokyo than in both nuclear strikes. Further resistance was useless. Given enough time the peace faction within the Emperor's war cabinet could have prevailed as Japan's people and infrastructure were slowly annihilated by American conventional arms.
The Manhattan Project was set up to produce nuclear bombs on an industrial scale, not just two. The Project cost $2bn, a huge amount of money in 1945. By the time the prototype was exploded, enough fissile material was being produced at Oak Ridge and Hanford to make several bombs a week. The United States, contrary to Oppenheimer's claim, could have afforded a demonstration first, as some Project scientists wanted. They were confident their technological wonder would work, and a demonstration would give the United States a defensible moral position against critics of its decision to use terror weapons against civilians. To not use such an expensive device against a fanatical enemy could have been characterized by Truman's political opponents as treasonous. Because it was dropped, and dropped twice, the US was able to occupy Japan alone as it could not do in Europe. We have been living with the fallout ever since*.
*The nuclear arsenals of Russia and the United States remain on hair-trigger alert. Mistakes, both human and machine, have led to several close calls since the Cold War began seventy years ago. November 9,1979: NORAD screens indicated a large-scale Soviet missile attack was underway. The US nuclear arsenal was immediately prepared for a retailiatory strike. However, satelite data failed to confirm any incoming missiles, so no strike was launched. The cause of the false signals discovered later was that a technician had inserted a training simulation into an operational NORAD computer. Opps! September 26,1983 a Soviet early warning satelite indicated five US nuclear missiles were headed towards the USSR. A Russian colonel looking at the telemetry decided it was a false alarm. He reasoned that the United States would not start a nuclear war by launching only five missiles at the Soviet Union. Investigation of the incident showed the satelite mistook sunlight reflecting from the tops of clouds as missle launches.