The President Intervenes

For the atomic bombs dropped on Hiroshima and Nagasaki, President Truman authorized their use when they were ready but did not get involved in target selection or timing.  Under the existing authorization the third bomb would be dropped at the discretion of the U.S. military.  On August 10, 1945, after being briefed on the impact of the first bombings, Truman altered his directive, requiring that any further use would require his "express authority".  Although Truman always publicly maintained the decision to drop the bombs was an easy one, there is also testimony from those working with him that he was disturbed at the extent of destruction and loss of life and took this action to regain direct control over the use of the next bomb.  It may also be that if, as he hoped, Japan would begin discussing surrender, he did not want another bomb used in the midst of such discussions.