Each of the home islands (casualties) would have to be taken with amphibious operations against battle-educated Japanese soldiers.**
**["From Beyond Bushido: Recent Work in Japanese Military History a symposium sponsored by the Center for East Asian Studies, the College of Liberal Arts and Sciences, the Office of International Programs, and the Departments of History and East Asian Languages and Cultures at the University of Kansas. Monday, February 16, 1998."]
The inevitable question, was using the atomic bomb justified?
Richard B. Frank's Downfall: the End of the Imperial Japanese Empire (Amazon link at atomic bomb) is a significant work in the ongoing debate over the two fateful days in nuclear warfare history, August 6th and 9th, 1945. Subsequently, the decision-making process has been scrutinized and criticized from every angle. The comparative advantage versus the comparative horror which resulted, the cold calculus of war, is a harsh reality for every commander in a total war. If dropping the bombs ended the war sooner, how much sooner, and how much more of a toll could the war have exacted on Japan and the Allies?
Downfall - From the Back Cover
Downfall opens with a vivid portrayal of the catastrophic fire raid on Tokyo in March 1945--which was to be followed by the utter destruction of almost every major Japanese city--and ends with the anguished vigil of American and Japanese leaders waiting to learn if Japan's armed forces would obey the Emperor's order to surrender.
America's use of the atom bomb has generated more heated controversy than any other event of the whole war:
Did nuclear weapons save the lives of hundreds of thousands of Americans poised to invade Japan?
Did U.S. leaders know that Japan was urgently seeking peace and needed only assurance about the Emperor's safety to end the war swiftly?
Was the bomb really used to intimidate the Russians?
Why wasn't the devastating power of the weapon demonstrated first before being unleashed on a city?
Richard B. Frank has brought to life these critical times, working from primary documents, reports, diaries, and newly declassified records. These pages present the untold story of how American leaders learned in the summer of 1945 that their compromise strategy to end the war by blockade and bombardment, followed by invasion, had been shattered; radio intelligence had unmasked a massive Japanese buildup on Kyushu designed to turn the initial invasion into a bloody shambles. Meanwhile, the text and analysis of diplomatic intercepts depicted sterile prospects for negotiation before a final clash of arms. Here also, for the first time, is a full and balanced account of how Japan's leaders risked annihilation by gambling on a military strategy aimed at securing political bargaining leverage to preserve the old order in Japan.
Downfall replaces the myths that now surround the end of the war and the use of the bomb with the stark realities of this great historical controversy.
Consider one mighty battle which never took place. The Japanese were stockpiling kamikaze suicide planes, among other weapons. The suicide planes, guided human bombs, had success sinking American ships in previous engagements. They exacted a toll standard Japanese aviation no longer could against heavily-defended capital ships.
Wikipedia - Operation Downfall
The Japanese defense relied heavily on kamikaze planes. In addition to fighters and bombers, they reassigned almost all of their trainers for the mission, trying to make up in quantity what they lacked in quality. Between them, the Army and Navy had more than 10,000 aircraft ready for use in July, and would have had somewhat more by October—and were planning to use almost all that could reach the invasion fleets.
During the Battle of Okinawa, less than 2,000 kamikazes had gotten about one hit per nine planes that made an attack. At Kyushu, given the more favorable circumstances, they hoped to get one for six. The Japanese estimated that the planes would sink more than 400 ships, and since they were training the pilots to target transports rather than carriers and destroyers, the casualties would be disproportionately greater than at Okinawa. One staff study estimated that the kamikazes could destroy a third to a half of the invasion force before its landings.
A graphic account of the plan of attack.
The Japanese had 58 more airfields on Korea, western Honshu and Shikoku, which also were to be used for massive suicide attacks.
Allied intelligence had established that the Japanese had no more that 2,500 aircraft of which they guessed that 300 would be deployed in suicide attacks.
In August 1945, however, unknown to Allied intelligence, the Japanese still had 5,651 army and 7,074 navy aircraft, for a total of 12,725 planes of all types. Every village had some type of aircraft manufacturing activity. Hidden in mines, railway tunnels, under viaducts and in basements of department stores, work was being done to construct new planes.
Additionally, the Japanese were building newer and more effective models of the Okka - a rocket-propelled bomb much like the German V-1, but flown by a suicide pilot.
When the invasion became imminent, Ketsu-Go called for a fourfold aerial plan of attack to destroy up to 800 Allied ships.
While Allied ships were approaching Japan, but still in the open seas, an initial force of 2,000 army and navy fighters were to fight to the death to control the skies over Kyushu. A second force of 330 navy combat pilots were to attack the main body of the task force to keep it from using its fire support and air cover to protect the troop carrying transports. While these two forces were engaged, a third force of 825 suicide planes was to hit the American transports.
As the invasion convoys approached their anchorages, another 2,000 suicide planes were to be launched in waves of 200 to 300, to be used in hour-by-hour attacks.
By mid-morning of the first day of the invasion, most of the American land-based aircraft would be forced to return to their bases, leaving the defense against the suicide planes to the carrier pilots and the shipboard gunners.
Carrier pilots crippled by fatigue would have to land time and time again to rearm and refuel. Guns would malfunction from the heat of continuos firing and ammunition would become scarce. Gun crews would be exhausted by nightfall, but still the waves of kamikazes would continue. With the fleet hovering off the beaches, all remaining Japanese aircraft would be committed to nonstop suicide attacks, which the Japanese hoped could be sustained for 10 days. The Japanese planned to coordinate their air strikes with attacks from the 40 remaining submarines from the Imperial Navy - some armed with Long Lance torpedoes with a range of 20 miles - when the invasion fleet was 180 miles off Kyushu.
The Imperial Navy had 23 destroyers and 2 cruisers which were operational. These ships were to be used to counterattack the American invasion. A number of the destroyers were to be beached at the last minute to be used as anti-invasion gun platforms.
Once offshore, the invasion fleet would be forced to defend not only against the attacks from the air, but would also be confronted with suicide attacks from the sea. Japan had established a suicide naval attack unit of midget submarines, human torpedoes and exploding motorboats.
The goal of the Japanese was to shatter the invasion before the landing. The Japanese were convinced the Americans would back off or become so demoralized that they would then accept a less-than-unconditional surrender and a more honorable and face-saving end for the Japanese.
But as horrible as the battle of Japan would be off the beaches, it would be on Japanese soil that the American forces would face the most rugged and fanatical defense encountered during the war.
The United States had a plan to blunt some of this kamikaze punch due to evolving intelligence alerting the high command of the reality of the threat.
Wikipedia - Operation Downfall
U.S. military intelligence initially estimated the number of Japanese aircraft to be around 2,500. The Okinawa experience was bad—almost two fatalities and a similar number wounded per sortie—and Kyushu was likely to be worse. To attack the ships off Okinawa, planes had to fly long distances over open water; to attack the ships off Kyushu, they could fly overland and then short distances out to the landing fleets. Gradually, intelligence learned that the Japanese were devoting all their aircraft to the kamikaze mission, and taking effective measures to conserve them until the battle. An Army estimate in May was 3,391 planes; in June, 4,862; in August, 5,911. A Navy estimate, abandoning any distinction between training and combat aircraft, in July was 8,750; in August, 10,290.
The Allies made preparations, adding more fighter squadrons to the carriers in place of torpedo- and dive-bombers, and converting B-17s into airborne radar pickets—the ancestors of the AWACS. Adm. Nimitz came up with a plan for a pre-invasion feint, sending a fleet to the invasion beaches a couple of weeks before the real invasion, to lure out the Japanese on their one-way flights, who would then find—instead of the valuable, vulnerable transports—ships loaded with antiaircraft guns from stem to stern.