In this concise account of why America used atomic bombs against Japan in 1945, J Samuel Walker analyses the reasons behind President Truman's most controversial decision. Delineating what was known and not known by American leaders at the time, Walker evaluates the options available for ending the war with Japan. In this new edition, Walker incorporates a decade of new research - mostly from Japanese archives only recently made available - that provides fresh insight on the strategic considerations that led to dropping the bomb. From the debate about whether to invade or continue the conventional bombing of Japan to Tokyo's agonising deliberations over surrender and the effects of both low and high level radiation exposure, Walker continues to shed light on one of the most earthshaking moments in history.