Answer:
President Truman removed General Douglas MacArthur, for MacArthur treated the Korean War as another World War, in which he had to destroy his opposition no matter the cost (it being the communist regime, and the weapon being nuclear weapons). Truman, on the other hand, knew of the delicate usage of the nuclear weapons, and if they are used, the USSR will counter. This led to Truman removing MacArthur for rash behavior.
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Well, they were over 8 miles away when the bomb detonated, so they wouldn't have seen any of the destruction. Even reconnaissance planes were initially unable to survey the extent of the destruction due to the enormous amounts of smoke caused by the fires, and dust brought up by the bomb.
Also the service ceiling for the B-29 is 31,850ft. 40,000ft would've been impossible.
