Some scientists associated with the Manhattan Project petitioned
President Truman not to use it against Japan unless certain specific conditions
were met. The text of the Szilard Petition, as it became known, is here.
The president did not respond formally to the petition. He did, however, confide
to his diary:
We have discovered the most terrible bomb in the history of the world. It may be the fire destruction prophesied in the Euphrates Valley Era, after Noah and his fabulous Ark.
Anyway we "think" we have found the way to cause a disintegration of the atom. An experiment in the New Mexico desert was startling - to put it mildly. Thirteen pounds of the explosive caused the complete disintegration of a steel tower 60 feet high, created a crater 6 feet deep and 1,200 feet in diameter, knocked over a steel tower 1/2 mile away and knocked men down 10,000 yards away. The explosion was visible for more than 200 miles and audible for 40 miles and more.
This weapon is to be used against Japan between now and August 10th. I have told the Sec. of War, Mr. Stimson, to use it so that military objectives and soldiers and sailors are the target and not women and children. Even if the Japs are savages, ruthless, merciless and fanatic, we as the leader of the world for the common welfare cannot drop that terrible bomb on the old capital or the new.
He and I are in accord. The target will be a purely military one and we will issue a warning statement asking the Japs to surrender and save lives. I'm sure they will not do that, but we will have given them the chance. It is certainly a good thing for the world that Hitler's crowd or Stalin's did not discover this atomic bomb. It seems to be the most terrible thing ever discovered, but it can be made the most useful...
-- Truman quoted in Robert H. Ferrell, Off the Record: The Private Papers of Harry S. Truman (New York: Harper and Row, 1980) pp. 55-56. Truman's writings are in the public domain.
Here is how the Target Selection Committee, chaired by General Groves at Los Alamos, discussed the question of choosing a target for the first bomb(s) in early May 1945:
6. Status of Targets
A. Dr. Stearns described the work he had done on target selection. He has surveyed possible targets possessing the following qualification: (1) they be important targets in a large urban area of more than three miles in diameter, (2) they be capable of being damaged effectively by a blast, and (3) they are unlikely to be attacked by next August. Dr. Stearns had a list of five targets which the Air Force would be willing to reserve for our use unless unforeseen circumstances arise. These targets are:
(1) Kyoto - This target is an urban industrial area with a population of 1,000,000. It is the former capital of Japan and many people and industries are now being moved there as other areas are being destroyed. From the psychological point of view there is the advantage that Kyoto is an intellectual center for Japan and the people there are more apt to appreciate the significance of such a weapon as the gadget. (Classified as an AA Target)
(2) Hiroshima - This is an important army depot and port of embarkation in the middle of an urban industrial area. It is a good radar target and it is such a size that a large part of the city could be extensively damaged. There are adjacent hills which are likely to produce a focussing effect which would considerably increase the blast damage. Due to rivers it is not a good incendiary target. (Classified as an AA Target)
(3) Yokohama - This target is an important urban industrial area which has so far been untouched. Industrial activities include aircraft manufacture, machine tools, docks, electrical equipment and oil refineries. As the damage to Tokyo has increased additional industries have moved to Yokohama. It has the disadvantage of the most important target areas being separated by alarge body of water and of being in the heaviest anti-aircraft concentration in Japan. For us it has the advantage as an alternate target for use in case of bad weather of being rather far removed from the other targets considered. (Classified as an A Target)
(4) Kokura Arsenal - This is one of the largest arsenals in Japan and is surrounded by urban industrial structures. The arsenal is important for light ordnance, anti-aircraft and beach head defense materials. The dimensions of the arsenal are 4100' x 2000'. The dimensions are such that if the bomb were properly placed full advantage could be taken of the higher pressures immediately underneath the bomb for destroying the more solid structures and at the same time considerable blast damage could be done to more feeblestructures further away. (Classified as an A Target)
(5) Niigata - This is a port of embarkation on the N.W. coast of Honshu. Its importance is increasing as other ports are damaged. Machine tool industries are located there and it is a potential center for industrial despersion. It has oil refineries and storage. (Classified as a B Target)
(6) The possibility of bombing the Emperor's palace was discussed. It was agreed that we should not recommend it but that any action for this bombing should come from authorities on military policy. It was agreed that we should obtain information from which we could determine the effectiveness of our weapon against this target.
B. It was the recommendation of those present at the meeting that the first four choices of targets for our weapon should be the following:
a. Kyoto
b. Hiroshima
c. Yokohama
d. Kokura Arsenal
C. Dr. Stearns agreed to do the following: (1) brief Colonel Fisher thoroughly on these matters, (2) request reservations for these targets, (3) find out more about the target area including exact locations of the strategic industries there, (4) obtain further photo information on the targets, and (5) to determine the nature of the construction, the area, heights, contents and roof coverage of buildings. He also agreed to keep in touch with the target data as it develops and to keep the committee advised of other possible target areas. He will also check on locations of small military targets and obtain further details on the Emperor's palace.
7. Psychological Factors in Target Selection:
A. It was agreed that psychological factors in the target selection were of great importance. Two aspects of this are (1) obtaining the greatest psychological effect against Japan and (2) making the initial use sufficiently spectacular for the importance of the weapon to be internationally recognized when publicity on it is released.
B. In this respect Kyoto has the advantage of the people being more highly intelligent and hence better able to appreciate the significance of the weapon. Hiroshima has the advantage of being such a size and with possible focussing from nearby mountains that a large fraction of the city may be destroyed. The Emperor's palace in Tokyo has a greater fame than any other target but is of least strategic value.
8. Use Against "Military" Objectives
A. It was agreed that for the initial use of the weapon any small and strictly military objective should be located in a much larger area subject to blast damage in order to avoid undue risks of the weapon being lost due to bad placing of the bomb.