Operation Downfall

• 1. Introduction

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  Operation Downfall was a plan that never happened, and the world may be fortunate for that. It was the Allied scheme to invade Japan's home islands near the end of World War II, a two-stage assault conceived by some of the most powerful military commanders in history. Had it gone forward, planners estimated it would have been the largest amphibious operation ever attempted, surpassing even the Normandy landings. The casualty projections were staggering. American losses alone ranged from hundreds of thousands to over a million. Japanese military and civilian deaths were projected in the millions, possibly the tens of millions. What kind of plan produces numbers like those? How did the Allies arrive at it? And what did the Japanese prepare in response? These are the questions that make Operation Downfall one of the most consequential plans never executed in military history.

• 2. The Plan Takes Shape

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  Responsibility for planning fell to Fleet Admiral Chester Nimitz, General of the Army Douglas MacArthur, and the Joint Chiefs of Staff, including Fleet Admirals Ernest King and William D. Leahy, and Generals George Marshall and Henry H. Arnold. The atomic bomb was, at this stage, a closely guarded secret known to only a few top officials outside the Manhattan Project. Initial invasion planning did not account for its existence at all.

  Interservice rivalry nearly derailed the effort before it began. The Navy wanted Nimitz in command; the Army wanted MacArthur. The dispute was serious enough to threaten the entire planning process. The Navy ultimately partially conceded, and MacArthur was to receive total command if circumstances required it.

  The Combined Chiefs of Staff, meeting at Quebec, agreed that Japan must be forced to surrender no more than one year after Germany's defeat. A joint planning team had earlier produced a document suggesting the invasion need not happen until 1947-48, but American planners argued that prolonging the war to such an extent would be dangerous for national morale.

  Geographically, Japan offered very few options. Most of its coastline was unsuitable for large-scale amphibious landings. Only Kyushu, the southernmost main island, and the beaches of the Kanto Plain near Tokyo offered realistic invasion zones. That constraint shaped everything that followed, and it shaped Japanese planning too.

• 3. Olympic and Coronet

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  Operation Olympic, the first stage, was scheduled to begin on the 1st of November 1945, designated "X-Day." The combined Allied naval armada would have included 42 aircraft carriers, 24 battleships, and 400 destroyers and destroyer escorts. Fourteen U.S. divisions plus a division-equivalent were assigned to the initial landings. Okinawa would serve as the staging base.

  Kyushu was to be attacked at three points: Miyazaki, Ariake, and Kushikino. The 35 landing beaches were all named after automobiles, from Austin through to Stutz, Winton, and Zephyr. After the name Operation Olympic was compromised by transmission in unsecured code, the operation was renamed Operation Majestic.

  A deception plan called Operation Pastel was designed alongside it. The goal was to convince the Japanese that the Allies had rejected a direct invasion and instead planned to encircle and bombard Japan from bases in Formosa and along the Chinese coast. The ruse was intended to redirect Japanese defensive attention before the real assault.

  Operation Coronet, the second stage, was tentatively set for the 1st of March 1946, "Y-Day." It targeted the Kanto Plain south of Tokyo on the island of Honshu. Coronet would have been even larger than Olympic, with up to 45 U.S. divisions assigned for the initial landing and follow-up. For comparison, the Normandy invasion deployed twelve divisions in the initial landings. The First Army would have struck at Kujukuri Beach on the Boso Peninsula while the Eighth Army landed at Hiratsuka on Sagami Bay. Allied forces would then have driven north and inland, encircling Tokyo and pressing toward Nagano.

• 4. Japan's Answering Plan

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  Japan's geography, which made the Allied invasion plan obvious to the planners, made it equally obvious to the Japanese. Their intelligence accurately predicted both the location and timing of the planned invasion before the United States had finalized those decisions. Unlike the Germans, who were deceived about the Normandy landings, the Japanese knew what was coming and prepared accordingly.

  The Japanese defensive scheme was called Operation Ketsugu, meaning roughly "Decisive" or "Final Battle." Beginning in June 1945, a propaganda campaign titled "The Glorious Death of One Hundred Million" urged every Japanese man, woman, and child to die for the Emperor when the Allies arrived. Japanese leaders believed they could make the cost of invasion high enough that the Allies would accept some form of armistice rather than demand total defeat.

  In March 1945, only one combat division stood in Kyushu. By August, formations including three tank brigades totaled 900,000 men on that island alone. Four veteran divisions were withdrawn from the Kwantung Army in Manchuria in March 1945 to reinforce the home islands. Between February and May 1945-45 new divisions were activated. By August, the Japanese Army had the equivalent of 65 divisions in the homeland but only enough equipment for 40 and ammunition for 30.

  For the civilian population, the Japanese organized the Volunteer Fighting Corps, drawing all healthy men aged 15 to 60 and women aged 17 to 40, totaling 28 million people. Weapons were scarce. Many were issued nothing better than bamboo or wooden spears. One mobilized high school girl, Yukiko Kasai, was issued an awl and told: "Even killing one American soldier will do. You must aim for the abdomen."

• 5. The Kamikaze Threat

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  Admiral Matome Ugaki was recalled to Japan in February 1945 and given command of the Fifth Air Fleet on Kyushu. The fleet was assigned the task of kamikaze attacks against ships in the invasion of Okinawa and began training pilots and assembling aircraft for the defense of Kyushu.

  At Okinawa, up to 2,000 kamikaze planes launched attacks and achieved approximately one hit per nine sorties. At Kyushu, Japanese planners hoped to raise that ratio to one in six. Terrain would reduce the Allies' radar advantage, and many of the aircraft to be used were wood-and-fabric training planes that Allied radar systems would have found difficult to detect. The Japanese estimated their planes would sink more than 400 ships. Because pilots were being trained to target transports rather than carriers and destroyers, casualties would be disproportionately heavy. One staff study estimated the kamikazes could destroy a third to half of the invasion force before it even reached the beaches.

  U.S. military intelligence initially estimated roughly 2,500 Japanese aircraft available. That figure climbed quickly as new intelligence arrived: 3,391 in May, 4,862 in June, 5,911 in August by Army estimates. A July Navy estimate, counting training aircraft alongside combat planes, put the total at 8,750, rising to 10,290 in August. By war's end, the Japanese actually possessed about 12,700 aircraft in the home islands, roughly half of them configured for kamikaze attack.

  The Allied counter-kamikaze strategy was called the Big Blue Blanket. It involved replacing torpedo and dive bombers on carriers with additional fighter squadrons and converting B-17s into airborne radar pickets. Admiral Nimitz also planned a pre-invasion feint, sending a fleet to the invasion beaches weeks early to lure kamikaze pilots out on their one-way flights, where they would encounter anti-aircraft-heavy warships instead of the vulnerable troop transports they were targeting.

• 6. Casualty Projections

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  On the 15th of January 1945, the Army Service Forces planning document projected that an average of 43,000 replacements for dead and evacuated wounded would be needed every month between June 1945 and December 1946. Projected Army losses alone totaled roughly 723,000 through the end of 1946 and 863,000 through early 1947, before accounting for Navy and Marine Corps casualties.

  Former President Herbert Hoover, a close friend of incoming President Harry S. Truman, submitted a memorandum on the 15th of May 1945, to Secretary of War Henry Stimson estimating that defeating Japan could cost 0.5 to 1.0 million American lives. Hoover and Truman met at the White House on May 28 and conversed for several hours. Truman then sought written assessments from Stimson, Undersecretary of State Joseph Grew, Fred Vinson, and Cordell Hull.

  On the Japanese side, physicist William B. Shockley published a worst-case estimate on the 21st of July 1945, projecting that at least 5 to 10 million Japanese, military and civilian combined, could die, with corresponding American casualties of up to 4 million. In August 1945, a gathering of roughly 50 reporters from the United States, Britain, and Australia was briefed off the record at MacArthur's Manila headquarters that final operations against Japan could produce up to a million American casualties.

  By war's end, nearly half a million Purple Heart medals had been stockpiled in anticipation of the invasion, with more in production. As late as 2003, approximately 120,000 medals from that stockpile remained unused. The scale of that preparation speaks plainly to what planners expected.

• 7. Chemical and Nuclear Weapons

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  Fears of "an Okinawa from one end of Japan to the other" drove planners to consider unconventional weapons. When a proposal for widespread chemical warfare reached President Truman in June 1945, he vetoed its use against personnel. Use against crops, however, remained under consideration.

  The Army had been experimenting with crop-destroying compounds since April 1944. Within one year, researchers narrowed more than 1,000 candidate agents down to nine based on phenoxyacetic acids. A compound designated LN-8 performed best in tests and went into mass production. A July 1945 test used an SPD Mark 2 bomb, originally designed for biological weapons like anthrax or ricin, to scatter the herbicide from the air. The ingredients in LN-8 and a second tested compound would later be used to create Agent Orange, employed during the Vietnam War.

  On the nuclear side, General Marshall ordered Major General John E. Hull to examine the tactical use of atomic weapons in support of the invasion. Colonel Lyle E. Seeman reported that at least seven Fat Man-type plutonium implosion bombs would be available by X-Day for use against defending forces. Seeman advised that American troops not enter a bombed area for at least 48 hours. The risk of nuclear fallout was not well understood at the time, and that interval would have exposed troops to substantial radiation.

  Manhattan Engineer District head Ken Nichols wrote that at the start of August 1945, planning had reached its final stages and the invasion, if it had occurred, might have been supported by roughly fifteen atomic bombs.

• 8. Why It Never Happened

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  Japan surrendered following the atomic bombings of Hiroshima and Nagasaki and the Soviet declaration of war on Japan in August 1945, which also triggered a Soviet invasion of Manchuria. Operation Downfall was canceled.

  The intelligence picture had been deteriorating sharply. Through April, May, and June 1945, Allied intelligence tracked Japanese ground force buildups with some complacency, projecting roughly 350,000 troops would be on Kyushu by November. That estimate collapsed in July with the discovery of four new divisions and indications of more coming. By August the count had risen to 600,000, and cryptanalysis from the Magic program had identified nine divisions in southern Kyushu alone, three times the expected number. MacArthur's intelligence chief, Major General Charles A. Willoughby, warned on July 29 that the buildup threatened to produce a situation "where we attack on a ratio of one to one, which is not the recipe for victory." By the time of surrender, more than 735,000 Japanese military personnel were in position or deploying on Kyushu alone.

  Admiral King was prepared to oppose the invasion and seek Nimitz's support for cancellation, which would have set off a major dispute within the U.S. government. Marshall, for his part, remained committed to invasion as late as August 15. The debate was never resolved militarily. Japan's surrender made it moot.

  The total strength of the Japanese military in the home islands at the time of surrender was 4,335,500 personnel, including 2,372,700 in the Army and 1,962,800 in the Navy. What a November 1945 landing would have encountered was a force far larger and more prepared than any Allied planner had anticipated when the operation was first conceived.