A map outlining the Japanese and U.S. (but not other Allied) ground forces scheduled to take part in the battle for Japan. Two landings were planned:
(1) Olympic—the invasion of the southern island, Kyūshū,
(2) Coronet—the invasion of the main island, Honshū.
|Objective||Invasion of Japan|
|Outcome||Cancelled after Japan surrendered in August 1945|
Operation Downfall was the overall Allied plan for the invasion of Japan near the end of World War II. The operation was canceled when Japan surrendered following the atomic bombing of Hiroshima and Nagasaki, and the Soviet Union's declaration of war against Japan.
Operation Downfall consisted of two parts—Operation Olympic and Operation Coronet. Set to begin in October 1945, Operation Olympic was intended to capture the southern third of the southernmost main Japanese island of Kyūshū, with the recently captured island of Okinawa to be used as a staging area.
Later, in the spring of 1946, Operation Coronet, was the planned invasion of the Kantō plain near Tokyo on the Japanese island of Honshū. Airbases on Kyūshū captured in Operation Olympic would allow land-based air support for Operation Coronet.
Japan's geography made this invasion plan obvious to the Japanese as well; they were able to accurately predict the Allied invasion plans and adjust their defensive plan, Operation Ketsugō, accordingly. The Japanese planned an all-out defense of Kyūshū, with little left in reserve for any subsequent defense operations.
|Air raids – Volcano & Ryukyu Is – Tokyo – Starvation – Tokyo Bay – Kure – Downfall – Hiroshima & Nagasaki – Kurils|
Responsibility for planning Operation Downfall fell to the U.S. commanders: Fleet Admiral Chester Nimitz, General of the Army Douglas MacArthur and the Joint Chiefs of Staff–Fleet Admirals Ernest King and William D. Leahy, and Generals of the Army George Marshall and Hap Arnold (the latter had a background in the U.S. Army Air Forces). At the time, the development of the atomic bomb was a very closely guarded secret known only to a few top officials outside the Manhattan Project, and planning for the invasion of Japan did not take its existence into consideration.
Throughout the Pacific War, and unlike the European theater, the Allies were unable to agree on a single Commander-in-Chief (C-in-C). Allied command was divided into regions: By 1945, for example, Chester Nimitz was Allied C-in-C Pacific Ocean Areas, while Douglas MacArthur was Supreme Allied Commander, South West Pacific Area. A unified command was deemed necessary for an invasion of Japan. Inter-service squabbling over who the Commander should be—the U.S. Navy wanted Nimitz, while the U.S. Army wanted MacArthur—was so serious that it threatened to derail planning. Ultimately, the Navy partially conceded, and MacArthur was to have total command of all forces, should circumstances made the invasion necessary.
The planners' primary considerations were time and casualties–namely how to force Japan's surrender as quickly as possible, with as few Allied casualties as possible. Prior to the 1943 Quebec Conference, a joint British-American planning team produced a plan ("Appreciation and Plan for the Defeat of Japan") which did not call for an invasion of the Japanese home islands until 1947–1948. The American Joint Chiefs of Staff believed that prolonging the war to such an extent was dangerous for national morale. Instead, at the Quebec conference, the Combined Chiefs of Staff agreed that Japan should be forced to surrender not more than one year after Germany's surrender.
The U.S. Navy urged the use of blockade and airpower to bring about Japan's capitulation. They proposed operations to capture airbases in nearby Shanghai, China, and Korea, which would give the U.S. Army Air Forces a series of forward airbases from which to bombard Japan into submission. The U.S. Army, on the other hand, argued that such a strategy could "prolong the war indefinitely" and expend lives needlessly, and therefore that an invasion was necessary. They supported mounting a large-scale thrust directly against the Japanese homeland, with none of the side operations that the Navy had suggested. Ultimately, the Army's viewpoint won out.
Physically, Japan made an imposing target, with few beaches suitable for invasion. Only Kyūshū (the southernmost island of Japan) and the beaches of the Kantō plain (both southwest and southeast of Tokyo) made suitable invasion zones. The Allies decided to launch a two-stage invasion. Operation Olympic would attack southern Kyūshū. Airbases would be established, and those would give cover for Operation Coronet, the attack on Tokyo Bay.
While the geography of Japan was fixed, the U.S. military planners could only estimate the defending forces they would face. Based on intelligence available early in 1945, their assumptions included the following:
Operation Olympic, the invasion of Kyūshū, was to begin on "X-Day," which was scheduled for November 1, 1945. The combined Allied naval armada would have been the largest ever assembled, including forty-two aircraft carriers, twenty-four battleships, and four hundred destroyers and destroyer escorts. Fourteen U.S. divisions were scheduled to take part in the initial landings. Using Okinawa as a staging base, the objective would have been to seize the southern portion of Kyūshū. This area would then be used as a further staging point to attack Honshū in Operation Coronet.
Olympic was also to include a deception plan, known as Operation Pastel. Pastel was designed to convince the Japanese that the Joint Chiefs had rejected the notion of a direct invasion and instead were going to attempt to encircle and bombard Japan. This would require capturing bases in Formosa, along the Chinese coast, and in the Yellow Sea area.
The U.S. Twentieth Air Force was to have continued its role as the main Allied strategic bomber force used against the Japanese home islands. Tactical air support was to be the responsibility of the U.S. Far East Air Forces (FEAF)—a formation which comprised the Fifth, Thirteenth and Seventh Air Forces—during the preparation for the invasion. FEAF was responsible for attacking Japanese airfields and transportation arteries on Kyūshū and Southern Honshū (for example, the Kanmon Tunnel) and for attaining and maintaining air superiority over the beaches.
Before the main invasion, the offshore islands of Tanegashima, Yakushima, and the Koshikijima Islands were to be taken, starting on X-5. The invasion of Okinawa had demonstrated the value of establishing secure anchorages close at hand, for ships not needed off the landing beaches and for ships damaged by air attack.
Kyūshū was to be invaded by U.S. Sixth Army at three points–Miyazaki, Ariake, and Kushikino. If a clock were drawn on a map of Kyūshū, these points would roughly correspond to 4, 5, and 7 o'clock, respectively. The 35 landing beaches were all named for automobiles: Austin, Buick, Cadillac through Stutz, Winton, and Zephyr. With one corps assigned to each landing, the invasion planners assumed that the Americans would outnumber the Japanese by roughly three to one. In early 1945 Miyazaki was virtually undefended, while Ariake with its nearby good harbor was heavily defended. Although Kushikino was weakly defended, its imposing terrain meant that the Marines who landed there would probably have had the toughest time.
The invasion was not supposed to conquer the entire island, just the southernmost third of it—indicated by the dashed line on the map, "general limit of northern advance." Southern Kyūshū would offer a staging ground and a valuable airbase for Operation Coronet.
Operation Coronet, the invasion of Honshū at the Kantō Plain south of the capital, was to begin on "Y-Day," which was scheduled for March 1, 1946. Coronet would have been the largest amphibious operation of all time, with 25 divisions (including the floating reserve) earmarked for the initial operations. U.S. First Army would have invaded at Kujūkuri Beach, on the Bōsō Peninsula, while U.S. Eighth Army invaded at Hiratsuka, on Sagami Bay. Both armies would then drive north and inland, meeting at Tokyo.
Olympic was to be mounted with resources already present in the Pacific, including the British Pacific Fleet, a Commonwealth formation that included at least a dozen aircraft carriers and several battleships. The Australian First Tactical Air Force took part in the Philippines campaign (1944–45). These would likely have augmented U.S. close air support units over Japan. The only major re-deployment for Olympic was Tiger Force, a Commonwealth long range heavy bomber unit, made up of 10 squadrons, scheduled to be transferred from RAF Bomber Command in Europe to airbases on Okinawa.
If reinforcements had been needed for Olympic, they could have been provided from forces being assembled for Coronet, which would have needed the redeployment of substantial Allied forces from Europe, South Asia, Australasia, and elsewhere. These would have included the U.S. First Army (15 divisions) and the Eighth Air Force, which were in Europe. The redeployment was complicated by the simultaneous partial demobilization of the U.S. Army, which drastically reduced the divisions' combat effectiveness, by stripping them of their most experienced officers and men.
According to U.S. historian John Ray Skates:
American planners took no note [initially] of the possibility that [non-U.S.] Allied ground troops might participate in the invasion of the Kanto Plain. They published plans indicated that assault, followup, and reserve units would all come from U.S. forces. [However, as] the Coronet plans were being refined during the [northern] Summer of 1945, all the major Allied countries offered ground forces, and a debate developed at the highest levels of command over the size, mission, equipment, and support of these contingents.
The Australian government requested the inclusion of Australian Army units in the first wave of Olympic, but this was rejected by U.S. commanders. Following negotiations among the western Allied powers, it was decided that a Commonwealth Corps, initially made up of infantry divisions from the Australian, British and Canadian armies would be used in Coronet. Reinforcements would have been available from those countries, as well as other parts of the Commonwealth. MacArthur blocked proposals to include an Indian Army division, because of differences in language, organization, composition, equipment, training, and doctrine. He also recommended that the corps should be organized along the lines of a U.S. corps, should use only U.S. equipment and logistics, and should train in the United States for six months before deployment; these suggestions were accepted. A British officer, Lieutenant General Sir Charles Keightley, had been nominated to lead the Commonwealth Corps. The Australian government questioned the appointment of an officer with no experience fighting the Japanese, and suggested that Lt. Gen Leslie Morshead should be appointed. The war ended before the details of the corps were finalized.
Meanwhile, the Japanese had their own plans. Initially, they were concerned about an invasion during the summer of 1945. However, the Battle of Okinawa went on so long that they concluded the Allies would not be able to launch another operation before the typhoon season, during which the weather would be too risky for amphibious operations. Japanese intelligence predicted fairly closely where the invasion would take place: southern Kyūshū at Miyazaki, Ariake Bay, and/or the Satsuma Peninsula.
While Japan no longer had a realistic prospect of winning the war, Japan's leaders believed they could make the cost of conquering Japan too high for the Allies to accept, leading to some sort of armistice rather than total defeat. The Japanese plan for defeating the invasion was called Operation Ketsugō (決号作戦 ketsugō sakusen) ("Operation Codename Decision").
Admiral Matome Ugaki was recalled to Japan in February 1945 and given command of the Fifth Air Fleet on Kyūshū. The Fifth Air Fleet was assigned the task of kamikaze attacks against ships involved in the invasion of Okinawa, Operation Ten-Go and began training pilots and assembling aircraft for the defense of Kyūshū where the Allies were likely to invade next.
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. Their 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. Ugaki also oversaw building of hundreds of small suicide boats that would also be used to attack any Allied ships that came near the shores of Kyūshū.
Fewer than 2,000 kamikaze planes launched attacks during the Battle of Okinawa, achieving approximately one hit per nine attacks. At Kyūshū, given the more favorable circumstances, they hoped to get one for six by overwhelming the U.S. defenses with large numbers of kamikaze attacks in a period of hours. The Japanese estimated that the planes would sink more than 400 ships; 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.
By August 1945, the Imperial Japanese Navy (IJN) had ceased to be an effective fighting force. The only Japanese major warships in fighting order were six aircraft carriers, four cruisers, and one battleship, none of which could be adequately fueled. The navy still had quite a large number of minor warships, but their use would also be limited by the lack of fuel. They could "sustain a force of twenty operational destroyers and perhaps forty submarines for a few days at sea."
In any amphibious operation, the defender has two options for defensive strategy—strong defense of the beaches, or defense in depth. Early in the war (such as at Tarawa) the Japanese employed strong defenses on the beaches with little or no manpower in reserve. This tactic proved to be very vulnerable to pre-invasion shore bombardment. Later in the war, at Peleliu, Iwo Jima, and Okinawa, the Japanese switched strategy and dug in their forces in the most defensible terrain. Fighting evolved into long battles of attrition, with very high American casualties, but no hope of victory for the Japanese.
For the defense of Kyūshū, the Japanese took an intermediate posture, with the bulk of their defensive forces a few kilometers inland from the shore—back far enough to avoid complete exposure to naval gunnery, but close enough that the Americans could not establish a secure foothold before engaging them. The counteroffensive forces were still further back, prepared to move against whichever landing seemed to be the main effort.
In March 1945, there was only one combat division in Kyūshū. Over the next four months the Imperial Japanese Army transferred forces from Manchuria, Korea, and northern Japan, while raising other forces in place. By August, they had fourteen divisions and various smaller formations, including three tank brigades, for a total of 900,000 men. Although the Japanese were able to raise large numbers of new soldiers, equipping them was more difficult. By August, the Japanese Army had the equivalent of 65 divisions in the homeland but only enough equipment for 40 and only enough ammunition for 30.
The Japanese did not formally decide to stake everything on the outcome of the Battle of Kyūshū, but they concentrated their assets to such a degree that there would be little left in reserve. By one estimate, the forces in Kyūshū had 40 percent of all the ammunition in the Home Islands.
In addition, the Japanese had organized the Patriotic Citizens Fighting Corps, which included all healthy men aged 15–60 and women 17–40 to perform combat support, and ultimately combat jobs. Weapons, training, and uniforms were generally lacking; some men were armed with nothing better than muzzle-loading muskets, longbows, or bamboo spears. Nevertheless, they were expected to make do with what they had.
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 Kyūshū was likely to be worse. To attack the ships off Okinawa, Japanese planes had to fly long distances over open water; to attack the ships off Kyūshū, 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 counter-Kamikaze preparations, known as the Big Blue Blanket. This involved adding more fighter squadrons to the carriers in place of torpedo- and dive-bombers, and converting B-17s into airborne radar pickets—similar to modern day AWACS. 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, instead of the valuable, vulnerable transports would find instead ships loaded with anti-aircraft guns from stem to stern.
The main defense against Japanese air attacks would have come from the massive fighter forces that were being assembled in the Ryukyu Islands. U.S. Army Fifth and Seventh Air Force and U.S. Marine air units had moved into the islands immediately after the invasion, and air strength had been increasing in preparation for the all-out assault on Japan. In preparation for the invasion, an air campaign against Japanese airfields and transportation arteries had commenced before the Japanese surrender.
Through April, May, and June, Allied intelligence followed the build-up of Japanese ground forces, including five divisions added to Kyūshū, with great interest but some complacency, still projecting that in November the total for Kyūshū would be about 350,000 servicemen. That changed in July, with the discovery of four new divisions and indications of more to come. By August, the count was up to 600,000, and Magic cryptanalysis had identified nine divisions in southern Kyūshū–three times the expected number. It turned out to be a serious underestimate of Japanese strength. Estimated troop strength in early July was 350,000, rising to 545,000 in early August.
The build-up of Japanese troops on Kyūshū led American war planners, most importantly General George Marshall, to consider drastic changes to Olympic, or replacing it with a different plan for invasion.
Because of its predictable wind patterns and several other factors, Japan was particularly vulnerable to gas attack. Such attacks would neutralize the Japanese tendency to fight from caves, which would only increase the soldiers' exposure to gas.
Although chemical warfare had been outlawed by the Geneva Protocol, neither the United States nor Japan were signatories at the time. While the United States had promised never to initiate gas warfare, Japan had used gas against the Chinese earlier in the war.
Fear of Japanese retaliation [to chemical weapon use] lessened because by the end of the war Japan's ability to deliver gas by air or long-range guns had all but disappeared. In 1944, Ultra revealed that the Japanese doubted their ability to retaliate against United States use of gas. "Every precaution must be taken not to give the enemy cause for a pretext to use gas," the commanders were warned. So fearful were the Japanese leaders that they planned to ignore isolated tactical use of gas in the home islands by the US forces because they feared escalation.
On Marshall's orders, Major-General John E. Hull looked into the tactical use of nuclear weapons for the invasion of the Japanese home islands (even after dropping two strategic atomic bombs on Japan, Marshall did not think that the Japanese would capitulate immediately). Colonel Lyle E. Seeman reported that at least seven bombs would be available by X-Day, which could be dropped on defending forces. Seeman advised that American troops not enter an area hit by a bomb for "at least 48 hours." (The risk of fallout was not well understood; this plan would have resulted in substantial radiation exposure for the American troops.
The Joint Staff planners, taking note of the extent to which the Japanese had concentrated on Kyūshū at the expense of the rest of Japan, considered alternate places to invade, including the island of Shikoku, or northern Honshū at Sendai or Ominato—or skipping the preliminary invasion and going directly at Tokyo. Attacking northern Honshū would have the advantage of a much weaker defense but at the cost of giving up land based air support (except the B-29s) from Okinawa.
General Douglas MacArthur dismissed any need to change his plans. "I am certain that the Japanese air potential reported to you as accumulating to counter our OLYMPIC operation is greatly exaggerated. … As to the movement of ground forces… I do not credit… the heavy strengths reported to you in southern Kyushu. … In my opinion, there should not be the slightest thought of changing the OLYMPIC operation." However Admiral Ernest King, the CNO, was prepared to officially oppose proceeding with the invasion, with Admiral Nimitz's concurrence, which would have set off a major dispute within the United States government.
At this juncture, the key interaction would likely have been between Marshall and Truman. There is strong evidence that Marshall remained committed to an invasion as late as 15 August. … But tempering Marshall's personal commitment to invasion would have been his comprehension that civilian sanction in general, and Truman's in particular, was unlikely for a costly invasion that no longer enjoyed consensus support from the armed services.
Unbeknownst to the Americans, the Soviets were preparing to follow up their invasions of Sakhalin and the Kuril Islands with an invasion of the weakly defended island of Hokkaidō by the end of August, which would have put pressure on the Allies to do something sooner than November. On August 15, the Japanese agreed to surrender, rendering the whole question of invasion moot.
In August 1945, the United States dropped the atomic bomb on Hiroshima and Nagasaki, resulting in the Japanese unconditional surrender. As a consequence, the invasion plans were unnecessary. Had the invasion been necessary, casualties would have likely been high on both sides.
Casualty predictions varied widely but were extremely high for both sides: depending on the degree to which Japanese civilians resisted the invasion, estimates ran into the millions for Allied casualties, and tens of millions for Japanese casualties.
Because the U.S. military planners assumed "that operations in this area will be opposed not only by the available organized military forces of the Empire, but also by a fanatically hostile population," high casualties were considered inevitable. Still, nobody knew with certainty how high. Several people made estimates, but they varied widely in numbers, assumptions, and purposes—which included advocating for and against the invasion—afterward, they were part of the debate over the atomic bombings of Hiroshima and Nagasaki.
Casualty estimates were based on the experience of the preceding campaigns, drawing different lessons:
Of these estimates, only Nimitz's included losses of the forces at sea, though kamikazes had inflicted 1.78 fatalities per kamikaze pilot in the Battle of Okinawa, and troop transports off Kyūshū would have been much more exposed.
Outside the government, well-informed civilians were also making guesses. Kyle Palmer, war correspondent for the Los Angeles Times, said half a million to a million Americans would die by the end of the war. Herbert Hoover, in memorandums submitted to Truman and Stimson, also estimated 500,000 to 1,000,000 fatalities, and were believed to be conservative estimates; but it is not known if Hoover discussed these specific figures in his meetings with Truman. The chief of the Army Operations division thought them "entirely too high" under "our present plan of campaign."
For context, the Battle of Normandy had cost 63,000 casualties in the first 48 days; and the Battle of Okinawa ran up 72,000 casualties over about 82 days, of whom 18,900 were killed or missing. Several thousand soldiers who died indirectly whether from wounds or other causes at a later date are not included. The entire war cost the United States a total of just over a million casualties, with 400,000 fatalities.
Nearly 500,000 Purple Heart medals were manufactured in anticipation of the casualties resulting from the invasion of Japan. To the present date, all the American military casualties of the sixty years following the end of World War II—including the Korean and Vietnam Wars—have not exceeded that number. In 2003, there were still 120,000 of these Purple Heart medals in stock. There are so many in surplus that combat units in Iraq and Afghanistan are able to keep Purple Hearts on-hand for immediate award to wounded soldiers on the field.
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