When did president Truman decide to drop the bombs?

Answer 1

The authorizations were all made in May 1945, when the Target List was prepared and the orders to "use the atomic bombs on Japan as they become available". As the Trinity Test had not yet been done, only the simpler MK-I "Little Boy" type atomic bomb was certain to work. It was unlikely that more than about 6 of these could be made before the end of 1945.

Following the successful Trinity Test the availability of MK-III "Fatman" type bombs (which though more complex could be manufactured in large numbers, as they needed much less fissile material) it was decided to cancel further production of the MK-I at the one already finished and produce only MK-III atomic bombs. This allowed the number of bombs to increase from about 6 to 23 that could be made before the end of 1945.

The only actual order that Truman gave about atomic bombs during the war was to cancel the already existing orders to use them, once Japan indicated they would surrender. The fact that they surrendered after only the first two probably caught Truman and many others completely by surprise. Based on prior experience most military leaders and US government officials sincerely believed it would be necessary for more than 90% of the Japanese population to die before the country would be unable to continue fighting (and US was willing to do whatever was needed to bring this about).

Answer 2

Truman became President of the United States on April 12, 1945, upon the death of President Franklin D. Roosevelt. The first atomic bomb was dropped on Japan on August 6, 1945.

Answer 3

After the Soviet Union declared war on Japan, Truman had only days to make up his mind.

Answer 4

These bombs were launched on August 6 and 9, 1945.

Answer 5

july 1945