Operation Downfall

Summary

Operation Downfall – the code name for the unrealized plan for an Allied (mainly American) invasion of the Japanese Islands at the end of World War II. The planned operation was cancelled when the Empire of Greater Japan surrendered after the atomic attacks on Hiroshima and Nagasaki and the Soviet Union”s entry into the war against Japan and its invasion of Manchuria. Operation Downfall was to consist of two parts under the code names Olympic and Coronet. The objective of Operation Olympic, scheduled to begin in November 1945, was to capture the southern part of Japan”s southernmost main island, Kiusiu, using the recently captured island of Okinawa to serve as a base for the invasion force. In early 1946, Operation Coronet, a planned invasion of the Kantō Plain, near Tokyo, on Japan”s largest island, Honsiu, was to begin. Air bases on Kiusiu captured during Operation Olympic would allow direct air support for Operation Coronet. Had this operation taken place, it would have been the largest amphibious landing operation in history.

Japan”s geography made the above invasion plan fairly obvious to the Japanese as well; they were able to accurately predict Allied moves and adjust their defensive plan accordingly, which was also in the pipeline: the Ketsugō operation. The Japanese had assigned most of their forces to the defense of Kiusiu, leaving few troops in reserve for any subsequent defensive operations. Casualty projections for the planned invasion varied widely, but were always extremely high. Depending on the extent to which Japanese civilians would resist the invasion, estimates ranged as high as millions of Allied casualties.

Responsibility for planning Operation Downfall fell to the highest American commanders: fleet admiral Chester Nimitz, army general Douglas MacArthur and the Joint Chiefs of Staff: fleet admirals Ernest King and William Leahy and army generals: George Marshall and Henry Arnold (the latter was commander of the U.S. Army Air Forces). At the same time, MacArthur”s promotion to the special “super grade” of six-star general (General of the Armies) was also under consideration, so that he would be given operational authority over other five-star generals. However, the proposal to promote MacArthur was only at the level of informal discussion when World War II ended.

At the time, the development of the U.S. atomic bomb was a closely guarded state secret (even then-Vice President Harry Truman did not know of its existence until he became president after Franklin Roosevelt”s death), known only to a few top officials outside the Manhattan Project, and planning for the invasion of Japan did not consider its use at all. When the atomic bomb became available, Gen. Marshall envisioned using it to support the invasion, in case enough of them could be produced in time.

Throughout the Pacific War, the Allies were unable to agree among themselves on a single Commander-in-Chief for all military forces. Allied command was divided by region: for example, Nimitz commanded the Pacific Ocean Areas, while MacArthur was Supreme Allied Commander, South West Pacific Area, and British Admiral Louis Mountbatten was Supreme Allied Commander, South East Asia Command. A unified command, however, was deemed necessary for the invasion of Japan. The rivalry between the armed forces over who should be the supreme commander (the U.S. Navy wanted Nimitz, but the U.S. Army preferred MacArthur) was so severe that it threatened to fiasco the entire invasion planning process. In the end, the Navy partially relented, and MacArthur was to be given complete command of all Allied forces if circumstances required.

Alternatives:ReflectionsConsiderationsDeliberationsReflecting

The main issues facing the planners were time and losses – how they could force Japan to surrender as quickly as possible with the fewest casualties on the Allied side. Prior to the Québec Conference in 1943, a joint Canadian-British-American planning team developed a Plan for the Defeat of Japan (“Appreciation and Plan for the Defeat of Japan”), which did not envision an invasion of the Japanese Islands until 1947-1948. The American Joint Chiefs of Staff, however, believed that prolonging the war to such an extent was dangerous to the morale of the nation. So instead, at a conference in Quebec, the Joint Chiefs of Staff agreed that Japan should be forced to surrender no later than one year after defeating Germany.

The U.S. Navy proposed using a naval blockade and heavy bombing by the Air Force to bring about Japan”s surrender. They proposed auxiliary operations to seize air bases in nearby Shanghai, China, and Korea, which would give the U.S. Army Air Forces a series of forward air bases from which to bomb Japan in an effort to force Japan to surrender. The Army, on the other hand, argued that such a strategy could “prolong the war indefinitely” and lead to unnecessary casualties, so an invasion was necessary. Army commanders advocated a large-scale strike directly against the Japanese Islands, without any of the side operations that the navy suggested. Ultimately, the Army point of view prevailed.

Geographically, Japan was a very challenging target, remote from other landmasses and with very few beaches suitable for launching a landing from the sea. Only Kiusiu (Japan”s southernmost island) and the beaches of the Kantō plain (both southwest and southeast of Tokyo) were convenient landing zones. Ultimately, the Allies decided on a two-stage invasion. Operation Olympic was intended to capture the southern part of Kiusiu. Air bases would be established there to provide direct air support for Operation Coronet, the attack on Tokyo Bay.

Alternatives:AssumptionsPremiseFoundationsPresumptions

Although Japan”s geography was well known, American military planners had to estimate the defensive forces they would face. Based on intelligence available in early 1945, their assumptions included the following:

Alternatives:OlympicOlympicsOlympianOlympia

Operation Olympic, the invasion of Kiusiu, was to begin on “Day X” (“X-Day”), which was scheduled for November 1, 1945. If it had happened, the combined Allied naval fleet would have been the largest ever assembled in one place up to that time, including 42 aircraft carriers, 24 battleships, and 400 destroyers and escort destroyers. Fourteen American “division equivalents” (13 divisions and two regimental combat teams) were to land on the very first day of the invasion. Using Okinawa as a forward base, the objective of the operation would be to seize the southern part of Kiusiu. This area would then be used as another advance point to attack Honsiu in Operation Coronet. Operation Olympic was also to include a disinformation component, known as Operation Pastel. It was intended to convince the Japanese that the Joint Chiefs of Staff had rejected the idea of a direct invasion and instead intended to encircle Japan and bomb it into surrender. This would require seizing bases on Formosa, along the Chinese coast, and in the Yellow Sea area.

The 5th, 7th, and 13th Air Armies were to be responsible for tactical air support during the coming invasion. They would be responsible for attacking Japanese airfields and transportation arteries on Kius and southern Honsiu (e.g., Kanmon Tunnel) and for gaining and maintaining air superiority over the beaches. The task of strategic bombing fell to the United States Strategic Air Forces in the Pacific (USASTAF), a formation composed of the 8th and 20th Army Air Forces and British Tiger Force. USASTAF and Tiger Force were to remain active during Operation Coronet as well. For the 20th Air Army, the task simply meant continuing its existing role as the main Allied bombing force used against the Japanese Islands, operating from airfields in the Marianas. After the end of the war in Europe in May 1945, there were also plans to move some heavy bomber groups from the experienced 8th Air Army to air bases on Okinawa to conduct strategic bombing raids in coordination with 20th Army. In doing so, the 8th Army was to replace its B-17 Flying Fortresses and B-24 Liberators with the more modern B-29 Superfortress (it received its first B-29 on 8 August 1945).

The invasion of Okinawa proved the value of establishing safe anchorages near the combat zone for ships not needed directly off the landing beaches and for vessels damaged by air attack. Therefore, the offshore islands of Tane-ga-shima, Yaku-shima, and Koshiki-jima were to be occupied prior to the main invasion, beginning on X – 5 (or the fifth day before the invasion).

Kius was to be attacked by the United States 6th Army at three points: at Miyazaki, Ariake, and Kushikino. If a clock were drawn on a map of Kiusiu, these points would roughly correspond to 4:00 a.m., 5:00 a.m., and 7:00 a.m. respectively. The 35 landing beaches were named after makes and popular car models of the time: Austin, Buick, Cadillac, and so on, up to Stutz, Winton, and Zephyr. With one corps assigned to each landing, invasion planners assumed that the Americans would outnumber the Japanese roughly three to one. Miyazaki was virtually undefended in early 1945, but Ariake with its good nearby port had strong protection. The invasion was not intended to conquer the entire island, only the southernmost third of it, as indicated by the dashed line on the map labeled “general limit of advance north.” South Kiusiu would provide a suitable beachhead and a valuable air base for Operation Coronet.

Coronet

Operation Coronet, the invasion of Honsiu across the Kantō Plain south of the capital, was to begin on “Y Day” (“Y-Day”), which was tentatively scheduled for March 1, 1946. Operation Coronet would have been larger even than Operation Olympic, involving up to 40 divisions dedicated both to the initial landing and to continuing inland operations. Had it come to fruition, it would have been undeniably the largest landing operation in history (by comparison, only 12 divisions were used for Operation Overlord in Normandy during the initial landing). During the initial phase, the 1st Army would land on Kujūkuri Beach on the Bōsō Peninsula, while the 8th Army would strike at Hiratsuka in Sagami Bay. Later, additional forces of up to 12 divisions from the 10th Army and the British Commonwealth Corps were to be provided as reinforcements. The Allied forces would then head north and inland, meeting at Tokyo.

Nor did U.S. planners initially plan to use any non-U.S. allied ground forces in Operation Downfall. If reinforcements were needed early in Operation Olympic, they would be detached from the U.S. forces being assembled for Operation Coronet – for which, in turn, there was to be a massive redeployment of units from the Southwest Pacific, China, Burma, India, and Europe. This would include such operational compounds as the US 1st Army (15 divisions) and the 8th Air Force. The Australian government requested at an early stage that an infantry division of the Australian Army be included in the first phase of the invasion (Olympic). However, the proposal was rejected by American commanders, and even the initial plans for Operation Coronet, according to American historian John Ray Skates, did not provide for units from the Commonwealth or other Allied armies to be landed on the Kantō Plain in 1946.

The first “official plans indicated that assault, first-line, and reserve units would come from American forces.” According to Skates, by mid-1945 – when plans for Operation Coronet were being intensively reworked – many other Allied nations “had offered their ground forces and a debate developed” among Western Allied political and military leaders “about the size, mission, equipment, and support of these contingents.” After negotiations, it was decided that Operation Coronet would also include the Commonwealth Corps, consisting of one infantry division each from the Australian, British, and Canadian armies. Reinforcements would be available from the above countries as well as from other Commonwealth countries. However, MacArthur blocked proposals to include an Indian Army division in the invasion force on the grounds that the differences in language, organization, composition, equipment, training, and doctrine were too great. He also recommended that the corps be organized along the lines of the U.S. corps, use only U.S. equipment and logistics, and train in the U.S. for six months before the invasion; all of these suggestions were accepted. The British government suggested that: The Commonwealth Corps should be commanded by Lieutenant General Charles Keightley, the combined Commonwealth Fleet should be led by Vice Admiral William Tennant, and that, as the Commonwealth air units would be dominated by Australian aviation, the officer commanding the air force should be Australian. However, the Australian government questioned the appointment of an officer with no combat experience against the Japanese, such as Keightley, and suggested that Lt Gen Leslie Morshead, an Australian who had campaigned in New Guinea and Borneo, should be appointed. The war ended before the details of the composition and command of this corps were settled. French troops were also to participate in the invasion.

Alternatives:Anticipated invasion forcesAnticipated invasion forceAnticipated invading forcesAnticipated invasive forces

The above figures for Operation Coronet do not include both the immediate reserves of 3 divisions and the projected 10-12 additional divisions that were to land as reinforcements.

Meanwhile, the Japanese had their own plans. The Empire feared that an invasion would occur in the summer of 1945, but the Battle of Okinawa had lasted so long that top Japanese commanders concluded that the Allies would not be able to launch another operation before the Pacific typhoon season, during which the weather would be too risky for landing operations. Japanese intelligence had fairly accurately predicted the location of the invasion: southern Kiusiu at Miyazaki, Ariake Bay and

While Japan no longer had a realistic prospect of winning the war, Imperial leaders believed they could make the costs of invading and occupying the Japanese Islands too high for the Allies to accept, which would lead to an armistice rather than total defeat. The Japanese defensive plan was called Operation Ketsu-gō (決号作戦, Ketsu-gō sakusen). Military commanders and politicians planned to rile up the entire Japanese population to resist the invasion, and a propaganda campaign calling for the “glorious death of a hundred million” began in June 1945. The main message of this campaign was that it was “glorious” to die for the divine emperor of Japan and therefore every Japanese, man, woman, and child, should die for the emperor when the Allies arrived. Although annihilation on this scale did not seem possible, both American and Japanese commanders at the time predicted millions of dollars in losses on both sides. Since losing the Battle of Saipan, Japanese propaganda intensified the narrative of patriotic death and portrayed the Americans as merciless “white devils.” During the Battle of Okinawa, Japanese officers ordered civilians unable to fight to commit suicide to avoid falling into American hands, and all available evidence suggests that the same orders would have been given in the Japanese Islands. The Japanese were secretly building an underground headquarters at Matsushiro in Nagano Prefecture to protect the Emperor and the Imperial General Staff during the invasion. In planning Operation Ketsu-gō, Japanese planners overestimated the strength of the invading troops: while the Allied invasion plan called for 54 divisions including reinforcements (14 for Operation Olympic and 38-40 for Operation Coronet), the Japanese expected as many as 90.

Alternatives:KamikazeThe Kamikaze

Adm. Matome Ugaki was recalled to Japan in February 1945 and assumed command of the 5th Air Fleet at Kiusiu. This formation was assigned to kamikaze attacks on ships involved in the invasion of Okinawa, Operation Ten-gō, and began training pilots and assembling aircraft intended for the defense of Kiusiu, the expected first target of the American invasion. The Japanese defense relied heavily on kamikaze. In addition to redeploying fighters and bombers to kamikaze units, they reassigned almost all of their new pilots to suicide missions. More than 10,000 aircraft were ready for use in July (even more were to be built by October), as well as hundreds of newly produced miniature Shin”yō submarines to attack Allied ships at sea. Up to 2,000 suicide pilots carried out attacks during the Battle of Okinawa, achieving about one hit per nine attacks. On Kiusiu, due to more favorable circumstances (such as terrain that would reduce the Allied radar advantage), the defenders hoped to raise that figure to one in six, overwhelming the U.S. fleet with a large number of kamikaze attacks in a matter of hours. The Japanese assumed that their planes would sink more than 400 ships, and because they trained their pilots to target carriers rather than aircraft carriers and destroyers, Allied losses would be disproportionately greater than at Okinawa. One study estimated that kamikaze pilots could destroy one-third to one-half of the invasion force even before landing.

Adm. Ernest King, commander of the U.S. Navy, was so concerned about the losses caused by the kamikaze attacks that he and other senior naval officers opted to call off Operation Downfall and instead wanted to continue the campaign of bombing Japanese cities and blockading food and supplies until the Japanese surrendered. However, Gen. George Marshall argued that forcing a surrender in this manner might take several years, if it occurred at all Accordingly, Marshall and Knox concluded that the Americans would have to invade Japan to end the war, regardless of casualties.

Alternatives:Naval forcesMaritime forces

Despite the devastating losses it had suffered by this point in the war, the Imperial Japanese Navy, then organized under the Naval General Command, was determined to inflict as much damage as possible on the Allies. When the fighting for Okinawa ended, the Japanese were left with only four battleships (all damaged), five damaged aircraft carriers, two cruisers, 23 destroyers, and 46 submarines. More than the weakness of the fleet, however, the Japanese were troubled by the fact that they lacked sufficient fuel for further forays on the high seas, so they planned instead to use the anti-aircraft firepower of their ships” artillery to defend naval installations while docked in port. Despite its inability to conduct large-scale fleet operations, the Japanese navy still maintained thousands of combat aircraft and had nearly 2 million personnel in the Japanese Islands, ensuring a large role in the upcoming defensive operation. In addition, Japan still had about 100 Kōryū-type miniature submarines, 300 smaller Kairyū-type miniature submarines, 120 kaiten live torpedoes, and 2412 Shin”yō suicide ships. Unlike the larger ships, these, along with the fleet”s destroyers and submarines, were to witness extensive coastal defense efforts to destroy some 60 Allied transport ships.

The Navy also trained a group of divers to serve as suicide bombers, fukuryū. They were to, armed with contact-fired mines, dive under landing ships and blow them up with themselves. A stockpile of such mines was placed on the sea floor at each potential invasion beach for use by the fukuryū; up to 10,000 mines were planned to be placed there. About 1,200 suicide divers were trained for the surrender of Japan.

Alternatives:Land forcesGround forces

Two possible options for defending against a landing invasion from the sea were to defend the beaches strongly or to withdraw and fight inland. During the Pacific War (at Tarawa, for example), the Japanese employed a strong beach defense, keeping little or no forces in reserve, but this tactic proved vulnerable to shoreline bombardment prior to invasion. Later, on Peleliu, Iwo Jima, and Okinawa, the defenders changed their strategy and dug their forces into more defensible terrain. On Kiusiu, the Japanese adopted an intermediate plan: most of their defensive forces were several kilometers inland, far enough away to avoid exposure to sea fire but close enough that the Americans could not gain a secure foothold before launching a deeper attack. Reserves earmarked for counterattack were even farther out, prepared to strike the largest grouping of invasion forces. In March 1945, only one combat division was stationed on Kius. Over the next four months, the Imperial Japanese Army moved units from Manchuria, Korea, and northern Japan while gathering other forces. By August, the Japanese already had 14 divisions and various smaller formations on the island, including three tank brigades, totaling 900,000 men. Although the Japanese were able to mobilize new troops, equipping them was more difficult. In August, the Japanese army at home had the equivalent of 65 divisions, but its equipment was only sufficient for 40 and ammunition for 30.

The Japanese command intended to organize the army personnel according to the following plan:

Alternatives:Air threatAirborne hazardsAir hazardAirborne threat

American military intelligence initially estimated the number of Japanese planes at about 2,500. Experience with enemy aviation on Okinawa had been very bad for the Americans-an average of nearly two fatalities and a similar number of ship injuries per kamikaze attack-and on Kiusiu the losses would probably be even heavier. To attack ships off Okinawa, Japanese planes had to fly long distances over the open ocean. To attack the ships off Kiuiu, they could fly most of the distance over land and then jump a short distance to the landing fleet. Gradually Allied intelligence learned that the Japanese were dedicating all their planes to kamikaze missions and were taking effective measures to preserve as many of them as possible for the invasion. The U.S. Army estimate for May was 3391 planes; for June, 4862; for August, 5911. The Navy estimate for July, ignoring any distinction between training and combat planes, was 8750; for August, 10,290. By the time the war ended, the Japanese actually had about 12,700 planes in the Japanese Islands, about half of them kamikaze.

Allied ship defense measures against the kamikaze, known as the Big blue blanket, called for adding more fighter squadrons to the carriers instead of torpedo planes and dive bombers, and converting B-17s into flying radars in a manner similar to today”s AWACS. Nimitz planned a pre-invasion diversion, sending the fleet toward the landing beaches weeks before the actual invasion to lure the kamikaze into their one-way flight, where they would find combat ships teeming with antiaircraft guns instead of valuable and air-prone transports. The main defense against Japanese air attacks would be provided by a massive fighter force (the 5th and 7th Air Arm and U.S. Marine Corps air units were to operate from the islands to bomb Japan.

Alternatives:Ground threatGround Threats

Through April, May, and June, Allied intelligence tracked the buildup of Japanese ground forces, including the five divisions sent to Kius, with great interest but also some complacency, still predicting that by November there would be a total of about 350,000 troops on Kius. This changed in July, with the discovery of four new divisions and evidence that more were coming. In August, the number reached 600,000, with cryptanalysts from the Magic team identifying nine divisions in southern Kiusiu – three times the expected strength. The estimate of Japanese troops in early July was 350,000, rising to 545,000 in early August.

Intelligence information about Japanese defensive preparations on Kius, which emerged in mid-July, caused powerful repercussions both in the Pacific and in Washington. On 29 July, MacArthur”s chief of intelligence, Maj. Gen. Charles Willoughby, was the first to note that April estimates allowed for Japan”s deployment of six divisions on Kiusiu, with the potential to deploy ten. “These divisions have come up since then, as predicted,” – he noted – “and no end is in sight. If this trend was not reversed, it threatened to “increase to the point where we will attack at a ratio of one (1) to one (1), which is not a recipe for victory.” At the time of the surrender, the Japanese had more than 735,000 troops in position or en route to battle stations on Kius alone. The total number of Japanese forces in the homeland was 4,335,500, with 2,372,700 in the army and 1,962,800 in the navy. The buildup of Japanese troops on Kius led American war planners, most notably Gen. George Marshall, to consider drastic changes to Operation Olympic or replacing it with another invasion plan.

Chemical weapons

Fears of an “Okinawa from one end of Japan to the other” led the Allies to consider using weapons other than typical weapons, including chemical weapons. Widespread chemical warfare was planned against the Japanese population using chemical weapons stockpiles accumulated in the Marianas. Due to several factors, including predictable wind directions, Japan was particularly vulnerable to gas attacks. Although large quantities of war gas have been produced in the U.S. and plans have been made for their use, it is unlikely that this would occur. Richard B. Frank states that when the proposal reached Truman in June 1945, the president vetoed the use of chemical weapons against humans; their use to destroy crops, however, was still under consideration. According to Edward J. Drea, the strategic use of chemical weapons on a massive scale was not considered or proposed by any senior American leader; rather, they debated the tactical use of chemical weapons against Japanese resistance groups.

Although chemical warfare was outlawed by the Geneva Protocol in 1925, neither the United States nor Japan was a signatory at the time. While the U.S. made unofficial declarations that it would never initiate chemical warfare, Japan used gas against the Chinese at the beginning of the Second Sino-Japanese War. As Roy Skates writes:

Until the surrender of Japan, the U.S. military considered chemical attacks to destroy agricultural crops in an attempt to take the Japanese by starvation. The Army began experimenting with crop-destroying specifics as early as April 1944, and in one year of testing limited the array of more than 1,000 chemicals to nine containing phenoxyacetic acids. One of these, designated as, LN-8, performed best in the tests and went into mass production. Dropping from a height or spraying herbicides on crops was considered the most effective; a test with the SPD Mark 2 bomb, originally designed to store biological weapons such as anthrax or ricin, conducted in July 1945 showed that a chemical container could be opened in the air to disperse the chemical. By the time the war ended, the Army was still trying to determine the optimum height to open the container to cover as wide an area as possible. Components of LN-8 and one of the other compounds tested were later used to create Agent Orange, used during the Vietnam War.

Alternatives:Nuclear weaponsNuclear weapon

At Marshall”s behest, Maj. Gen. John Hull explored the possibility of tactical use of nuclear weapons in an invasion of the Japanese Islands, even after dropping two atomic bombs on Hiroshima and Nagasaki (Marshall did not think the Japanese would capitulate immediately thereafter). Col. Lyle E. Seeman reported that at least seven Fat Man plutonium bombs would be available by X-Day to be dropped on Japanese defenses. He also warned that U.S. troops would not be allowed to enter the nuclear strike area for “at least 48 hours” after the explosion; this means that the threat of radioactive fallout was not yet well understood at that time, because entering the contaminated area so soon after the detonation would expose U.S. troops to significant doses of radiation.

Ken Nichols, district engineer for the Manhattan Engineer District, wrote that in early August 1945, “planning for the invasion of the Japanese Islands had reached its final stages and if the landing actually took place, about fifteen atomic bombs could be delivered for support . It was decided to detonate the bomb in the air at an altitude of 550-610 meters above the ground to achieve maximum detonation effects and to minimize residual radiation on the ground, since it was expected that American troops would soon occupy the areas attacked by nuclear weapons.

Alternatives:Alternative objectivesAlternative goalsAlternative targetsAlternate objectives

Planners at the College of the Joint Chiefs of Staff, given the degree to which the Japanese had concentrated forces on Kiusiu at the expense of the rest of Japan, also considered alternative invasion sites such as Sikoku Island, northern Honsiu at Sendai, and Ōminato. They also considered skipping the initial invasion of Kiusiu and going straight to Tokyo. An attack on northern Honsiu would have been easier because of its much weaker defenses, but would have had the disadvantage of lacking direct air support from Okinawa (these remote areas were within range of only B-29s).

Opportunities to change the Olympic operations plan

Gen. Douglas MacArthur rejected the need to change his plans:

However, Adm. Ernest King, Chief of Naval Operations, was prepared to oppose the continuation of the invasion, with Admiral Nimitz”s approval, which would have caused a major dispute within the U.S. government.

Alternatives:Soviet plansThe Soviet plans

Without the knowledge of the Americans, the Soviet Union was also considering launching its own invasion of the Japanese island of Hokkaido by the end of August 1945, which would certainly have put pressure on the Western Allies to launch an invasion earlier than November.

In the early years of World War II, the Soviets planned to expand the Red Fleet to catch up with the fleets of Western nations. However, the German invasion of the Soviet Union in June 1941 forced the suspension of this plan: The Soviets had to devote most of their resources to fighting the Germans and their allies, mainly on land, which they did for most of the war, leaving their fleet relatively poorly equipped. Therefore, as part of Project Hula (1945), the United States provided the Soviet Union with approximately 100 warships out of 180 planned for use after the USSR entered the war against Japan in the future. The delivered vessels also included landing ships.

At the Yalta Conference (February 1945), the Allies agreed that the Soviet Union would occupy the southern part of the island of Sakhalin, which Russia had ceded to Japan under the Treaty of Portsmouth after the Russo-Japanese War of 1904-1905 (the Soviets controlled its northern part), and the Kurile Islands, which had been assigned to Japan under the Treaty of St. Petersburg of 1875. On the other hand, no agreement provided for Soviet participation in the invasion of the Japanese Islands. The Japanese had many kamikaze planes on southern Honsiu and Kiusiu that would have resisted Olympic and Coronet operations. The extent to which they could counter Soviet landings in the far north of Japan is unknown. By comparison, the Western Allies committed about 1,300 warships during the Battle of Okinawa, of which 368 ships, including 120 amphibious ships, were severely damaged and another 28, including 15 landing ships and 12 destroyers, were sunk, mostly by kamikaze. The Soviets had fewer than 400 ships, most of which were not equipped for landing operations when the USSR declared war on Japan on August 8, 1945.

For Operation Downfall, the U.S. command projected that more than 30 divisions were needed for a successful invasion of the Japanese Islands. By comparison, the Soviet Union had about 11 divisions available in the Far East, comparable to the 14 divisions the Americans were to use only in the invasion of southern Kiusiu. The Soviet invasion of the Kuril Islands (August 18-September 1, 1945) had already taken place after Japan”s surrender on August 15, but some Japanese forces on the islands offered fierce resistance. In the Battle of Shumshu (August 18-23, 1945), the Red Army fielded 8821 troops, with no tanks and no support from major warships. The well-prepared Japanese garrison numbered 8500 soldiers and about 77 tanks. The battle lasted one day, with four more smaller combat actions following the official surrender of Japan and the garrison, during which the attacking Soviet forces lost more than 516 soldiers and 5 of their 16 landing ships (many of which had previously belonged to the U.S. Navy and were later transferred to the Soviet Union) to Japanese coastal artillery fire, and the Japanese lost more than 256 soldiers. Soviet losses during the Battle of Shumshu totaled up to 1,567, while the Japanese suffered 1018 casualties, making Shumshu the only battle in the 1945 Soviet-Japanese War in which Soviet losses exceeded Japanese losses.

During World War II, the Japanese had a naval base at Paramushir in the Kurile Islands and several bases in Hokkaido. Since Japan and the Soviet Union maintained a “tentative” neutrality toward each other until the USSR declared war on Japan in August 1945, Japanese observers stationed in Japanese-occupied territories in Manchuria and Korea, as well as Sakhalin and the Kuril Islands, constantly watched the port of Vladivostok and other seaports in the Soviet Union.

According to Thomas B. Allen and Norman Polmar, the Soviets carefully drew up detailed plans for invading the Far East, with the exception of the Hokkaido landing, which “existed in detail” only in Stalin”s mind, and it is “unlikely that the Soviet leader had any interest in seizing Manchuria (which he ceded to the Chinese shortly after the war), much less Hokkaido. Even if he wanted to seize as much territory as possible on the Asian continent, he was more focused on establishing a foothold in Europe than in Asia.”

Because American military planners assumed that “operations in the area of the Japanese Islands would be opposed not only by the available organized forces of the Empire, but also by fanatically hostile civilians,” high losses were considered inevitable, but no one knew with certainty how high they would be. Several estimates were made, but they varied widely in numbers, assumptions, and objectives, which also included the strength of resistance to the invasion. The estimated casualty figures later became a key point in the postwar debate about the justness of the atomic attack on Hiroshima and Nagasaki in the United States and elsewhere.

In preparation for Operation Olympic, the invasion of southern Kiusiu, various individuals and organizations estimated the expected number of casualties based on the terrain, strength, and disposition of known Japanese forces. However, as intelligence reported, enemy forces in the Japanese Islands continued to grow, and with them casualty estimates. In April 1945, the Joint Chiefs of Staff formally adopted an invasion plan, giving a scale of possible losses based on experience from both the European and Pacific battles. Given the size of the invasion force, consisting of 766,700 men, and the assumption that the campaign would last 90 days, it could be expected that the Sixth Army would lose 149,046 men (including 28,981 killed and missing) assuming the “European Experience” – “European Experience” – i.e., lessons learned from the battles with Germany and Italy (a ratio of 0.42 killed and missing and 2.16 total casualties per 1,000 troops per day of operations) or 514,072 casualties (including 134,556 killed and missing) using the “Pacific Experience” – i.e., past struggles with the Japanese (1.95 killed and missing and 7.45 total casualties

As time went on, other U.S. commanders made their own estimates:

In addition to the government and military, well-informed civilians in the United States were also developing their estimates of losses in a possible future invasion of Japan. Kyle Palmer, a war correspondent for the Los Angeles Times, wrote that between half a million and a million Americans would die by the end of the war. Herbert Hoover, in memoranda submitted to Truman and Stimson, also estimated the death toll at between 500,000 and 1 million, which he considered a conservative estimate; however, it is not known whether Hoover discussed these specific numbers in meetings with Truman. The Chief of Army Operations considered them “far too high” under “our present campaign plan.”

In evaluating these estimates, especially those based on the projected strength of the Japanese defenders, it is important to take into account what was known about the state of Japanese defenses at the time, as well as the current state of those defenses (MacArthur”s staff believed that Japanese troop strength on Kius was expected to be around 300,000 men). In anticipation of the casualties caused by the invasion of Japan, nearly 500,000 Purple Heart medals were produced (a number that exceeded the number of all American casualties of combat operations in the 65 years following the end of World War II, including the Korean and Vietnam Wars. In 2003, 120,000 of these Purple Hearts were still in storage. There were so many left that combat units fighting in Iraq and Afghanistan were able to obtain “second-war” Purple Hearts to immediately award to wounded soldiers.

Following the surrender of Japan and the demobilization of Imperial troops, vast quantities of war materiel were transferred to the United States occupation forces in the Japanese Islands and South Korea. While some numbers (especially for items such as swords and small arms) may be inaccurate due to disarmament problems and black market activity, the amount of military equipment available to the Japanese in and around the Japanese Islands by August 1945 looked roughly as follows:

Sources

  1. Operacja Downfall
  2. Operation Downfall