In the first three months of 1945, Japan’s military leaders forged a strategy they called Ketsu Go (Operation Decisive) to obtain the political bargaining chips to terminate the war in a manner they could abide. They were confident that no amount of blockade and bombardment, even if it cost the lives of millions of their countrymen, could compel them to yield. Moreover, they believed an impatient American populace would propel their antagonist to avoid a protracted siege and attempt to end the war swiftly. That dictated an invasion of the Japanese homeland.
Japanese strategists next examined the map in light of American operational habits. The United States could be expected to bring its huge preponderance of air strength to bear in support of an invasion. Land-based aircraft constituted the majority of U.S. air assets and thus dictated that the invasion must fall on an area within range of land-based fighter aircraft. From the positions the Japanese expected their opponent to hold by the summer of 1945, the nearest bases would be Okinawa and Iwo Jima. Okinawa, but not Iwo Jima, could support thousands of tactical aircraft, smaller than the B-29s that were already bombing the home islands. From Okinawa, American flyers could reach Kyushu and parts of Shikoku. Of these two, Kyushu offered the better set of potential air and sea bases from which to mount an attack on the obvious supreme objective—Tokyo, the political and industrial hub of Japan. A simple scan of the topographical map of Kyushu easily revealed to Japanese commanders three of the four chosen American invasion sites. Thus, the Japanese anticipated not only an invasion, but the two most probable invasion areas, the sequence of the two probable invasions, and the exact landing sites on Kyushu.
With a firm grasp of the strategic essentials, Japan embarked on a massive mobilization program. By midsummer there would be sixty divisions and thirty-four brigades mustering 2.9 million men in the homeland. A strict conservation program, plus the conversion of the aviation training establishment into kamikaze units, yielded the Japanese over 10,000 aircraft, half suicide planes, to confront the invasion. These forces were arrayed with primary emphasis on defending southern Kyushu and Tokyo.
By comparison to the tortured, military-dominated Japanese political structure, its well-designed American counterpart placed ultimate authority in civilian hands. But those hands changed on April 12, 1945, with the death of Franklin D. Roosevelt, which thrust Harry S Truman into the presidency. Roosevelt signally failed to ready Truman for his responsibilities, so the new president turned to his senior advisers for guidance on political and military strategy. Truman’s military advisers, however, were not in accord on the strategy to end the war.
The United States Navy, led by Fleet Admiral Ernest King, had reached a number of fundamental conclusions about the conduct of a war with Japan based on decades of intense study. None of these precepts was more deeply held than the principle that it would be absolute folly to invade Japan. Naval officers calculated that the United States could never mount expeditionary forces across the Pacific that would even equal the manpower Japan would mobilize to defend the homeland and the terrain would wholly negate American advantages in heavy equipment and vehicles. Therefore, entrenched Navy doctrine held that the sound way to bring a war with Japan to a close was by a campaign of blockade and bombardment, including intense aerial bombing.
When the United States Army, led by General George C. Marshall, came to focus attention belatedly on how to bring a war with Japan to a close, it swiftly adopted the view that only an invasion could bring the conflict to an acceptable conclusion. After extended debate over these competing views, the Joint Chiefs of Staff reached an unstable compromise in April 1945. The army secured ostensible approval for a two-phase invasion campaign, code-named Operation Downfall. The first phase, Operation Olympic, set for November 1, 1945, involved a landing designed to secure approximately the southern third of Kyushu. This would provide air and naval bases to support a second amphibious assault, Operation Coronet, set for March 1, 1946, aimed to secure the Tokyo region.
The Joint Chiefs justified this strategy on the basis that the overall American war aim was an unconditional surrender that would assure that Japan never again posed a threat to peace. But history raised formidable doubts about the practicality of that goal. No Japanese government had capitulated in 2,600 years; no Japanese detachment had surrendered in the entire course of the Pacific War. Accordingly, there was no guarantee either that a Japanese government would ever capitulate, or that Japan’s armed forces would bow to such a command. Thus, the American nightmare was not the initial invasion of the homeland, but the prospect that there would be no organized capitulation of Japan’s armed forces, over four million strong. Indeed, the official rationale for the invasion plan declared that it would be more likely than blockade and bombardment to produce the capitulation of Japan’s government, and it would best position the United States to deal with the situation if Japan’s armed forces did not surrender.
The navy obtained agreement that the campaign of blockade and bombardment would continue at an accelerating rate for six months prior to Olympic. Admiral King, however, explicitly warned his colleagues on the Joint Chiefs in April that he only concurred that orders for an invasion must be issued promptly so that all the preparations for such a gigantic enterprise could be mounted. He warned that the Joint Chiefs would revisit the necessity for an invasion in August or September.
Radio intelligence proved King prescient. During July and August, ULTRA unmasked for American leaders the ambush awaiting Olympic. The 680,000 Americans, including fourteen divisions, slated for the invasion of Kyushu had been expected to confront no more than 350,000 Japanese, including eight to ten divisions. But decrypted communications identified fourteen Imperial Army divisions as well as a number of tank and infantry brigades—also at least 680,000 strong—most positioned on southern Kyushu. Moreover, rather than only 2,500 to 3,000 aircraft to support their ground troops against 10,000 American planes, the ULTRA sources and photographic evidence revealed the Japanese had at least 5,900 to more than 10,000 aircraft, half of them kamikazes, waiting to pummel the invasion convoys.
Soviet intervention would have reshaped the burgeoning American debate over strategy to end the war in August 1945. The most likely result would have been to discard Olympic for a draft plan to invade northern Honshu in an attempt to prevent the Soviets from overrunning more of Japan. Once this operation was complete, however, American leaders would have balked at the prospect of conquering the remainder of the home islands, hole by hole, rock by rock. The devastating results of the blockade and bombardment strategy, as revealed from radio intelligence and other sources, would have argued for the navy strategy of starving Japan into submission. Only the possibility of liberating some POWs and internees would have roused interest in further land campaigns in Japan, so long as they remained limited with acceptable losses. Rising American frustration and fury would likely have sparked the decision to unleash chemical warfare against the 1946 rice crops, as well as succeeding ones—a project under consideration in 1945. The use of poison gas against Japan in support of the invasion had also been under consideration in 1945. The prospect of an endless continuation of the war to annihilate Japanese detachments in the home islands may have lifted that taboo as well. American air power and logistics, but not ground forces, would have aided the Allies in defeating Japanese units on the Asian continent.
The Pacific War would have dragged on for probably two to five more years—perhaps longer. The overall cost would have easily exceeded five million deaths in Japan alone by conservative estimates, and equal or double that number among all the nations and peoples caught in this protracted agony. While there would have been no division of Korea and hence no Korean War, there would have been a sharply divisive Soviet- American rivalry in the home islands to match the one along the uneasy borders of Europe. The surviving Japanese people would have languished in poverty and bitterness for decades. Thus the atomic bomb, for all its horror, was the “least abhorrent choice.”