President Harry Truman’s use of atomic weapons against the Japanese cities of Hiroshima and Nagasaki remains one of the most controversial decisions in the history of warfare. As with all historical events, Truman’s decision can be properly evaluated only in light of circumstances that existed in 1945. With these circumstances in mind, good evidence exists on both sides of the controversy.

Truman’s defenders have argued, foremost, that the atomic bomb ultimately saved US and Japanese lives because, without it, the US would have launched a costly invasion of the Japanese home islands. In this scenario, the Japanese would have defended their islands to the end. Throughout the Pacific War, the Japanese had fought with relentless and even “suicidal” ferocity given the kamikaze air attacks (beginning in October 1944), in which Japanese pilots resorted to intentionally crashing their planes into US warships. In the spring and summer of 1945, the Battle of Okinawa resulted in high casualties on all sides, including Okinawan civilians. Therefore, a reasonable assumption was that an invasion of Japan, which might have occurred as early as November 1, 1945, would have cost many thousands of lives.

On the other hand, Truman’s critics have contended that no such invasion would have occurred.