The decision to drop the first atomic bomb on Hiroshima in August, 1945, has been debated ever since. President Harry S. Truman concluded that the bomb would shorten the war and save many American lives. On the small, volcanic island of Iwo Jima, the United States had taken 26,000 casualties, including 6,800 deaths.
Some of the scientists who had worked to produce the atomic bomb in The Manhattan Project were getting cold feet about using it against Japan. The original logic had been that a ruthless Germany might be developing the same weapon and would have no qualms about using it. With the defeat of Nazi Germany, the complexion changed. Secretary of War Simpson appointed a committee of physicists that included Glenn Seaborg and Leo Szilard to study the potential uses of atomic power. Published in deep secrecy in June 1945, the Franck report, named after its less well-known chairman James Franck, offered a new perspective.
The physicists expressed their concern not for the lives of Japanese that might be lost, or the lives of American soldiers that might be saved. Their view was that the overriding issue was the long term avoidance of an atomic arms race. Noting that while the technique of bomb production might be exclusively in the possession of the United States, the underlying physics was widely understood and that should the United States use the weapon against a civilian population, the country would lose its future credibility as a neutral possessor of history`s greatest military secret.
The report correctly estimated that it would take another nation three or four years to reach the level of development that the United States had achieved already achieved, and ten years to draw even. This analysis was borne out by the successful test by the Soviet Union of an atomic weapon in 1949 and its detonation of a hydrogen bomb in 1953.
The abstract concept of avoiding a future arms race was probably never a practical political option for the Truman administration. According to declassified documents dating to the time, projections for an invasion of the mainland of Japan in Operation Downfall ran to a million American casualties. In this context, destroying two medium-sized Japanese cities could be regarded as the least of the available evils.
In early August, the Japanese government was deeply divided on the question of further resistance. The War Party insisted that Japan could still mount a successful defense of its mainland. Although time might have produced a surrender without the bomb, American preparations for the invasion were proceeding apace. It would have been impossible to turn the timetable on and off while waiting for a Japanese answer.
In fact, although the destruction wrought by the atomic bombs was instantaneous and spectacular, it was not completely outside the scale of wartime experiences. The fire bombing of Dresden and Tokyo had been intended to inflict death on a vast scale. In each case, deaths were numbered in the tens of thousands.
Finally, there is the simple fact that the Manhattan Project had cost about two billion dollars. It can be strongly argued that the American people would expect a "return" on this investment by using the weapon. The Franck Report noted that the American people had recognized in the case of poison gas weapons that some weapons need to be developed but not willingly used, even to shorten the war. This might have been their response to withholding the atomic bomb, or using it in a demonstration setting.
The first successful test, code named Trinity, was conducted on July 16, in New Mexico. Knowing that this weapon was in hand, the Allies issued an ultimatum to Japan at the Potsdam Conference in Germany that they would only accept unconditional surrender.
In early August, the Japanese government was deeply divided on the question of further resistance. The War Party insisted that Japan could still mount a successful defense of its mainland. Although time might have produced a surrender without the bomb, American preparations for the invasion were proceeding apace. It would have been impossible to turn the timetable on and off while waiting for a Japanese answer.
On August 6, the United States dropped the first atomic weapon ever used in a military campaign on the city of Japanese. No exact casualty count is possible, but estimates range from 90,000 to 160,000 dead, with about half on the first day and the remainder from lingering effects of radiation and other injuries.
Sixteen hours later, President Truman announced the bombing to the nation. For the first time, he revealed the massive scale of the Manhattan Project, which had reached 125,000 employees during the peak of construction. With the Japanese having not yet surrendered, Truman outlined their prospects:
If they do not now accept our terms they may expect a rain of ruin from the air, the like of which has never been seen on this earth. Behind this air attack will follow sea and land forces in such number that and power as they have not yet seen and with the fighting skill of which they are already well aware.Not receiving the response it demanded, the United States unleashed its only other operational atomic bomb on Nagasaki on August 9. Around 40,000-60,000 people died as a result. On August 14, the Empire of Japan surrendered unconditionally. V-J day, the official end of World War II, took place on August 15, 1945.
The formal signing of the surrender documents took place on board the U.S.S. Missouri on September 2 in Tokyo Harbor, not far from where Admiral Perry had induced the Japanese to open their country to Western influence almost a century earlier. General Douglas MacArthur, who received the surrender, broadcast a message to the American people, in which he offered the hope that the Japanese nation could lifted from its destruction to resume its proper place among the nations of the world. This result was achieved through the occupation of Japan that continued until 1952.