http://www.lehigh.edu/~ineng/enola/content/gar.htm

Especially important has been the 1979 discovery of President Truman's "lost" diary. This and other documents suggest that the president fully understood that the "jolt" of the expected early August Russian declaration of war would so shock Japan that the fighting would end: After Stalin confirmed Russia would soon declare war against Japan, for instance, President Truman privately noted in his diary: "Fini Japs when that comes about." And writing to his wife the next day, he observed that with the Soviet declaration "we'll end the war a year sooner now, and think of the kids who won't be killed!"