Truman returned to Washington from Potsdam on the evening of 7 August and was immediately caught up in a whirlwind of activity generated by Groves, who was determined to proceed as quickly as possible with a second bombing of Japan. He and Admiral William Purnell, Groves writes in his autobiography, 'had often discussed the importance of having the second bomb follow the first one quickly', so that the Japanese would not have time to recover their balance'. This second bomb would have to be of the Fat Man type, there being no chance of assembling another uranium bomb at this stage (in fact, the Little Boy remained one of its kind; the Fat Man design, despite its complicated assembly, being easier to manufacture, safer to transport and more powerful). After the success of the Trinity test, the only thing standing in the way of using a Fat Man bomb in Japan was the availability of plutonium. Groves had originally been advised that a plutonium bomb could be ready to use on August 20. At the end of July, this was revised to 11 August. Groves, however, was too impatient to wait that long and, somewhat against the advice he was given by the scientists, saw to it that the bomb was assembled, loaded and ready to use by the evening of 8 August [...]
Immediately after the Nagasaki bombing the Allies did not possess any more atomic bombs. It is true, as Groves puts it, 'our entire organization both at Los Alamos and at Tinian was maintained in a state of complete readiness to prepare additional bombs', but, as he himself reported to General Marshall, the earliest data at which the next bomb could be assembled for use was 17 August, and almost everybody expected the war to be over by then.
