(This statement was broadcast to the nation shortly after the the first atomic bomb was used against Hiroshima.  In this message President Truman outlines the reasons why he authorized the US military to use the atomic bomb.)
 

Sixteen hours ago an American airplane dropped one bomb on Hiroshima, an important Japanese Army base.  That bomb had more power than 20,000 tons of T.N.T.  It had more than two thousand times the blast power of the British "Grand Slam" which is the largest bomb ever yet used in the history of warfare.

The Japanese began the war from the air at Pearl Harbor.  They have been repaid many fold.  And the end is not yet.  With this bomb we have now added a new and revolutionary increase in destruction to supplement the growing power of our armed forces.  In their present form these bombs are now in production and even more powerful forms are in development.

It is an atomic bomb.  It is a harnessing of the basic power of the universe.  The force from which the sun draws its power has been loosed against those who brought war to the Far East.

We are now prepared to obliterate more rapidly and completely every productive enterprise the Japanese have above ground in any city.  We shall destroy their docks, their factories, and their communications Let there be no mistake; we shall completely destroy Japan's power to make war.

It was to spare the Japanese people from utter destruction that the ultimatum of July 26 was issued at Potsdam.  Their leaders promptly rejected that ultimatum.  If they do not now accept our terms they may expect a rain of ruin from the air, the like of which has never been seen on this earth.  Behind this attack will follow sea and land forces in such numbers and power as they have not yet seen with the fighting skill of which they are already aware....

The fact that we can release atomic energy ushers in a new era in man's understanding of nature's forces.  Atomic energy may in the future supplement the power that now comes from coal, oil, and falling water, but at present it cannot be produced on a basis to compete with them commercially.  Before that comes there must be a long period of intensive research....
 

Source:  Department of State Bulletin, 1945.