20 Steps in Planning for the Invasion of Japan in 1945

2. The Navy initially opposed the invasion before committing what would have been the largest invasion fleet in history

By the late summer of 1945, in what turned out to be the last two weeks of the war, battleships and cruisers were bombarding the home islands of Japan. The bombardments were primarily by ships of the US Navy, supported by the Royal Navy and the Royal New Zealand Navy, and the damage inflicted to Japanese industry and infrastructure was extensive. When the Japanese did not strike at the bombarding ships the Allies committed destroyers to the bombardment operations. Meanwhile, shipping to and from Japan, as well as between the islands of the nation, was brought to a near standstill. The bombardment’s effectiveness, as well as the lack of Allied casualties, led the Navy to support a strategy of blockade, rather than invasion.

MacArthur argued for invasion, believing that a blockade could be a lengthy process, and would have a deleterious effect on American morale, especially with some American troops coming home from the European theater. Once the decision was made that the invasion would go forward, the Navy committed a force of 24 battleships and 42 aircraft carriers, supported by four hundred destroyers and destroyer escorts, itself a testament to the massive American industrial expansion in World War II. By comparison, the Japanese fleet had 5 battleships, all damaged and lacking the fuel to leave their moorings, and five aircraft carriers, in the same relatively helpless position.

3. The planners did not realize the extent of the Japanese kamikaze forces

The reason that the Japanese did not respond with air attacks against the bombarding ships and carrier strikes against their home islands is that they were converting the majority of their remaining air forces to kamikaze planes to be used against the invasion armada, which they knew from experience would be massive. The Japanese had nearly 10,000 planes available for kamikaze attacks (two thousand had been used at Okinawa, causing heavy losses) and several hundred suicide boats. Japanese planners intended to use the kamikazes primarily against troop transports in the invasion fleet in a sort of air-based banzai wave of attacks.

Although the number of kamikazes available was not known until after the surrender, the absence of air defenses launched against the Americans led Admirals Nimitz and King to argue against invasion and for blockade, aware of the heavy casualties which could be inflicted on both the Army and the Navy before any troops even got ashore in Japan. The Chiefs-of-Staff were unaware of the near readiness of the atomic bomb, but they were aware of the fire raids launched by LeMay from the Marianas. Further raids hit other cities from bases in China. George Marshall, urged by MacArthur, made the decision to move forward with planning for Operation Downfall.

4. The United States had plans to use chemical weapons if necessary

Neither the United States nor the Empire of Japan were signatories to the Geneva Protocol banning the use of chemical weapons, and the Japanese used poison gas in China earlier in the war. During the island-hopping campaign across the Pacific, the Japanese had changed their defensive tactics. Early in the war, the Japanese defended the beachheads, attempting to prevent US troops from establishing a position ashore. Later in the war, as the pre-invasion air and ship bombardments grew more deadly, the Japanese established positions inland, in caves and underground bunkers, where there was an element of protection from the bombardments.

Gas weapons were prepositioned in the Marianas, to be delivered to the troops after landing and to be dropped by B-29s prior to the invasion. Troops underground, unless they were in sealed bunkers with closed air systems, would be especially vulnerable to gas weapons, given the prevailing nature of the winds over the Japanese Islands. The United States planners also considered the use of chemical weapons against Japanese crops. A defoliant designated LN-8 was developed over the course of the war and was considered for use before the Japanese surrender rendered it unnecessary. Following the war, LN-8 was one of the chemicals which was developed into Agent Orange.

5. The Soviets planned an invasion of Hokkaido in August 1945

At the Yalta Conference, Franklin Roosevelt secured a promise from Stalin to invade Japan, which was reiterated to Truman during the Potsdam Conference. Allied invasion planners in the Pacific were unaware that the Soviets were planning to keep that promise with an invasion of Hokkaido. In the spring of 1945, the United States initiated Project Hula, in which 180 ships were to be transferred to the Soviet Union via the Aleutians. The ships included landing craft, transport vessels, escort vessels, mine sweepers, and other support vessels. Since the Soviets had minimal experience with invasion from the sea, American and British advisors accompanied the ships.

American planners were aware of Soviet intentions in the Kuril Islands and the Sakhalin peninsula, by the planned invasion of Hokkaido, one of the major Japanese home islands, was unknown to the Americans. The Soviets went forward with their invasion of the Kuril Islands, attacking on August 18, 1945 – three days after the Japanese surrender. Fighting continued until September 1, with the Japanese troops in the islands offering a clue as to what could have been expected during an invasion of Kyushu. On August 23, under orders of the Japanese command, the majority of the troops surrendered, but isolated units continued to resist. The Soviets suffered about 2,000 casualties (out of 15,000 engaged) in what amounted to a Stalin land grab.

6. MacArthur wanted the invasion to be an all American operation

Douglas MacArthur has been accused many times of having an enormous ego which sometimes overrode his judgment, but in the case of Operation Downfall, his arguments for the invading troops to be all Americans were sound. They were based on logistics. In an operation so large (Downfall would have been the largest seaborne invasion in history) logistical problems, particularly resupplying the troops engaged in battle with ammunition and other supplies, were inevitable. The British and Australian troops used different weapons, of different calibers than the Americans. This included rifles, sidearms, machine guns, tanks, artillery, and virtually everything else.

American planners depended on reinforcing and resupplying Olympic with units from Coronet if necessary, themselves redeployed from other Pacific theaters of operation. Nonetheless, in the early summer of 1945, Commonwealth forces were committed to participation in Operation Coronet, though MacArthur insisted that they be equipped with American weapons. MacArthur also demanded that units of the Indian Army not be included, to which the planners acquiesced. MacArthur’s argument against the use of Indian troops was based on the difference in language, which he believed could cause communication issues detrimental to his overall command of the ground forces.

7. Commonwealth Air Forces were to operate from bases in Okinawa

Planners for Operation Olympic created a joint Commonwealth air group designated Tiger Force. Tiger Force was to have consisted of Royal Air Force, Royal Canadian Air Force, Royal Australian Air Force, and Royal New Zealand Air Force units, as well as veteran aircrews from Bomber Command in England. Among them was the 617 squadron, known as the Dam Busters, who would be used for special air operations, such as the destruction of Japanese bunkers. Tiger Force was to have been equipped with Avro Lancasters, Avro Lincolns, and the American-built Consolidated B-24 Liberator. They were to be supported with Hawker Tempest fighters, and P-51 Mustangs flown by American pilots.

Among the plans for Tiger Group was inflight refueling, using a process developed by the British before the war using converted Halifax tankers. Inflight refueling had been used prior to the war over the Atlantic using the system to be deployed at Okinawa, but development had been curtailed during the war in Europe, and inflight refueling had yet to be attempted during combat. Nevertheless, it was necessary to increase the range of the British bombers in order to make them effective against Japan, allowing them to strike targets and return to their base in Okinawa. In addition to the ground-based bombers, the British were to supply 18 aircraft carriers, 25% of the sea-based airpower.

8. Veterans of the air war against Germany were to be transferred to the Pacific

Even before the collapse of Nazi Germany in 1945, planners for Operation Downfall were involving the veteran Eighth Air Force, which had carried the bulk of the American strategic bombing campaign against the Third Reich. Plans were for several of the heavy bombing groups of the Eighth Air Force to transfer to bases in the Pacific to be re-equipped with the B-29, which carried a crew of 11 rather than the 10 of the B-17, and which had a different defensive system. After the necessary training, the European veterans were to operate out of Okinawa as part of the United States Strategic Air Forces in the Pacific, which also had control of the Commonwealth’s Tiger Force.

The American Twentieth Air Force, which was already the main strategic bombing force operating against the Japanese, was to continue its strategic bombing of Japanese targets from its bases in the Marianas. Other aerial support provided by the United States Army Air Forces were tactical, used to bombard the defenses on the beachheads and further inland as range allowed. The tactical groups were scheduled to be moved to airbases in the captured portion of Kyushu, and then to support operations during Coronet. In all operations, aircraft from the massive carrier force were to provide both air cover and close ground support, a tactic developed by the Navy and Marines as the war evolved.

9. The Americans decided to deceive the Japanese with a diversionary plan

The argument for blockading and bombarding the Japanese into starvation and eventual submission was considered sound enough that planners for Operation Downfall decided to create a diversion which made it appear that they were adopting that strategy. The deception plan was designated Operation Pastel. Pastel was designed to convince the Japanese that the Allies had decided not to invade the Japanese homeland and were instead planning on striking Japanese bases in China, to tighten the ring surrounding the home islands. Pastel included the creation of fictional units of the USAAF and supporting British and Commonwealth forces.

The main thrust of Operation Pastel was the reduction of Formosa and its use as a staging base for aerial raids against Japanese positions on the Chinese mainland while a major invasion force was assembled, to strike at multiple positions in China. Operation Pastel included dummy airborne landings, similar to those used successfully in Operation Overlord in Europe. The entire intent of Operation Pastel was to convince the Japanese that a threat to their homeland from Okinawa was non-existent, in the hope that southern Kyushu, the most likely target of an invasion staged from Okinawa, would not be reinforced and fortified.

10. MacArthur demanded overall command of all forces involved in the invasion

Throughout the Pacific war, overall command of the forces in the huge theater was divided. Unlike in Europe, where supreme authority was held by Eisenhower as the commander of Supreme Headquarters Allied Expeditionary Forces in Europe (SHAEF) the Pacific had Admiral Chester Nimitz in command of the Central Pacific, General MacArthur as commander in the Southwest Pacific, and Lord Louis Mountbatten in command of the China Burma India (CBI) theater. Both MacArthur and Nimitz wanted the authority for the proposed invasion of Japan, and their chiefs in Washington were divided over which it should be, based on longstanding American inter-service rivalries.

A proposal arose, most likely from MacArthur, that a temporary rank is created for him which would make him senior in authority over all other service ranks. The idea of whether or not to appoint MacArthur as a sort of Generalissimo, which would also make him senior in theory to the Joint Chiefs of Staff, never went beyond the discussion phase, and according to Admiral Ernest King, the Naval Chief of Operations, was never under serious consideration. In the final event, Nimitz agreed to place the Navy under MacArthur’s authority only if the situation on the ground in Japan dictated such a necessity, for example, if it was necessary to withdraw the invading troops in the event of a repulse.

11. Japan offered few suitable beaches for attack

Unlike the coast of France, where the Allies had several potential landing points and Hitler himself was convinced that the invasion would come at a place other than Normandy, Japan had few beaches where a seaborne invasion could land. The complex two-pronged plan for Operation Downfall evolved as a necessity given the opportunities offered. American planners had to consider the speed of completing the invasion in the shortest time possible given the difficulties encountered as a result of Japan’s distance from points of resupply. The planners also had to consider the casualties which they would incur, and the fighting on Okinawa and in the Philippines indicated they would be considerable.

The planners picked three main points as the targets for Operation Olympic, with 35 landing beaches, code-named after automobile manufacturers. Planners assumed that the troops going ashore would outnumber the defenders by a factor of 3:1, when in fact some areas were heavily defended and others had no defenders at all, other than coast watchers. Prior to the invasion of Kyushu, three offshore islands were to be taken, beginning in the last week of October 1945. These islands were intended to provide anchorages for vessels damaged during the assault itself and in the actions supporting the troops after the beachheads were obtained, a necessity learned during the fight for Okinawa when so many ships crowded offshore presented an array of targets for the kamikazes.

12. Kyushu was to be Japan’s main point of defense

The planning for Operation Downfall was that Kyushu was to be a preliminary operation, establishing a staging area for the main invasion of Japan in Honshu. Fourteen divisions were assigned to Operation Olympic, tasked with landing on the beaches, driving inland and capturing intact the port facilities, and securing airfields. They were then to develop a defensive perimeter after capturing about one-third of the island. By contrast, twenty-three divisions were assigned to the invasion of Honshu in Operation Coronet, where the main defense of the home islands was expected. American planners believed they would find Kyushu relatively lightly defended, with much stiffer resistance expected on Honshu.

In fact, beginning in the spring of 1945, the Japanese began reinforcing Kyushu, planning on making the battle where the main focus of their defense of the home islands. Well aware that victory was impossible, the Japanese hoped to inflict severe casualties in a protracted campaign which would lead to a negotiated peace. Troops were recalled from Manchuria and Korea, and others were transferred from Honshu. By late summer 1945 there were fourteen divisions deployed in Kyushu, and another nearly two million armed civilians, trained by Japanese troops in methods of killing unsuspecting Americans. Japan’s troops were not all fully equipped for combat in 1945, but an arms buildup was underway.

13. The Glorious Death of One Hundred Million campaign in Japan

After the fall of Okinawa, despite continuing resistance in the Philippines, it was evident to the Japanese that an invasion of the home islands was coming. Japanese military leadership developed a plan of resistance, designated Ketsugo, meaning Decisive. As part of the defensive operations, the Japanese planners enlisted the support of the entire civilian population of the home islands, in a propaganda campaign which began while the fighting on Okinawa was still underway. The campaign called for the “Glorious Death of One Hundred Million” men, women, and children, rather than allowing any American to desecrate the islands of Japan.

The propaganda campaign stressed that dying for the emperor, who was also in Japanese minds a god, was a glorious death which would be honored by one’s ancestors and rewarded in the afterlife. To die gloriously for the god/emperor was preferable to living in shame while the emperor was destroyed. At the same time the emperor was venerated, the Americans were depicted as monstrous animals, who were likely to kill all the civilians anyway, after rapine and torture. Both Japanese and American planners estimated Japanese deaths would be in the millions as a result of the invasion and the preliminary bombardments.

14. The Americans dropped leaflets warning the Japanese people of bombings

During the war, the B-29 raids, which increased over the summer of 1945 and were to increase further in the buildup for Operation Downfall, were preceded by warnings. Leaflets which came to be known as Lemay Leaflets were dropped on Japanese cities warning them of impending bombing raids and reminding them that the Americans were at war with the “military clique” and not the Japanese people. The leaflets were necessary because Japan’s war machinery was located within residential communities, surrounded by homes, shops, and schools. The leaflets reminded the Japanese that the Americans did not “…wish to injure innocent people.”

Similar leaflets were dropped over Japanese cities warning of the atomic bomb and the destructive power which was about to be released on the Japanese, though not specifying the cities to be targeted with an atomic attack. Following the Hiroshima bombing, leaflets were dropped which told the Japanese to enquire as to the damage caused by the single bomb, while warning of further bombings to follow. The leaflets were contraband among the Japanese and were the target of further propaganda to counter their message, which was that the Americans weren’t quite the monsters the Japanese leadership made them out to be.

15. The Japanese were well prepared for the invasion by August 1945

To face the incoming American invasion the Japanese had amassed ten thousand kamikaze aircraft. At Okinawa, the Japanese scored an average of one hit on an American ship for every nine kamikazes launched. By late October the number of kamikazes available would have increased, though the number of available pilots by the scheduled time of the American invasion remains unknown. Japanese planning established a goal of one-hit per six launches, and the newly trained pilots were directed to target American troop transports. Japanese planners estimated that up to 400 American ships could be damaged or sunk before discharging their troops.

As was revealed after the war, the Japanese had accurately identified the beaches to be targeted by the Americans and had positioned their defenses to maximum effect. Unlike other invasions of the Second World War, there was to be no battle for air superiority, since the Japanese had converted their entire air defenses to offensive suicide weapons. The Japanese also had about 400 midget submarines, which like the kamikazes were expected to deploy in one-way missions against the invasion fleet, supported by manned torpedoes and more than 2,000 suicide boats. Although no official decision was made for the main battle to be on Kyushu, in the aftermath of its defense Japan would have expended most of its remaining assets.

16. The atomic bomb accelerated invasion planning

The first atomic bomb was dropped over Hiroshima on August 6, 1945. Even before the second bombing at Nagasaki on August 9, invasion planners were incorporating the use of the bomb as part of Operation Downfall. The Joint Chiefs had begun adding atomic weapons to the plans following the successful Trinity test of the device in July. George Marshal requested a report on the number of weapons that would be available by November 1 and a recommendation regarding their use on Japanese troop concentrations in Kyushu. The report was requested because the Americans had begun to notice the concentration of Japanese assets in the invasion areas.

Nimitz and King, also concerned by the apparent increases in Japanese aircraft strength and assuming they were to be used as kamikaze weapons, recommended bypassing the Kyushu phase of Operation Downfall and concentrating on one of the northern islands. King was for canceling the invasion altogether. MacArthur was unconcerned with the reports of Japanese strength and recommended moving the invasion date up. “I am certain that the Japanese air potential reported to you as accumulating to counter our Olympic operation is greatly exaggerated,” he wrote to Marshall. MacArthur also discounted the reports of Japanese troop strength and continued to urge invasion.

17. The United States planners faced a suicidal enemy

The Japanese tactics of fighting to the death on the ground, coupled with the suicidal tactics of the Japanese air fleet and navy, were the greatest concern for the planners. While MacArthur dismissed them out of hand, the reports of the Japanese troop buildup in Kyushu were supported by Magic intercepts and the analyses of members of MacArthur’s own staff. Nonetheless, he continued to argue forcefully for a seaborne invasion, submitting unrealistically low casualty estimates, which he argued would be lower than those sustained in the Philippines, since the best Japanese troops were already eliminated. Marshall continued to support the invasion officially, though privately he expressed doubts about its necessity.

Meanwhile, Admirals King and Nimitz altered the makeup of the carrier air groups to be assigned for the invasion fleet. The torpedo groups were to be removed from the carriers and replaced with fighter squadrons. On more than half the carriers the bomber groups were also to be removed, likewise replaced with fighters. This move would have given the Navy an increased air defense against the incoming kamikazes, which could be engaged and hopefully shot down before they were in sight of the fleet and the troopships. The fleet also officially adopted the Big Blue Wave of constant air patrols which had been put into effect at Mindoro during the invasion of the Philippines.

18. The Japanese drafted men as old as sixty, and women as old as forty

To aid the troops and sailors in the resistance to the American invasion of the home islands, the Japanese created the Volunteer Fighting Corps during the summer of 1945. All males between the ages of 15 and 60, and all females between 17 and 40, were conscripted by the governor of the prefecture in which they lived. The Corps was intended to be the second line of resistance, carrying out guerrilla warfare in the mountains and in cells in the cities and towns in the event the Americans overran areas of Japan. This would have included the port cities which were targets of Operation Olympic, and the third of Kyushu of which American occupation was a goal.

The formation of the Volunteer Fighting Corps gave Japan access to 28 million additional fighters, although by the end of the war only about two million were trained and organized into units. Units of the Volunteer Fighting Corps never saw action against the Americans since the invasion of Japan never happened, but some units did fight against the Soviets after they invaded Manchuria near the end of the war, as well as in Korea and Sakhalin. They also fought and sustained heavy casualties against the Soviets in Manchukuo. Often armed with simple bamboo spears, they like their military counterparts usually fought to the death.

19. Casualty estimates of an invasion were widely disparate

In May 1945, Admiral Nimitz directed his staff to prepare a casualty estimate based on the known Japanese defenses at the time. His staff estimated 49,000 casualties in the first 30 days of an invasion of Kyushu, including 5,000 at sea. In contrast, MacArthur’s staff estimated less than half the number of casualties in the first 30 days, and a total of 125,000 in four months, at which point the US Army would assume a defensive posture in preparation to support Operation Coronet. MacArthur’s estimate was based on fighting what he claimed was the true number of combat troops on Kyushu, approximately 300,000 men. In fact, there were over 900,000 combat troops present, with more on the way.

In conference with President Truman, George Marshall reported that American casualties would be about 20% of those sustained by the Japanese on Kyushu, which he assumed would be the entire force of 350,000. His estimate was thus 70,000 American casualties. But the real strength of the Japanese force was over 900,000, making American casualties 180,000. Neither MacArthur’s nor Marshall’s estimates included naval casualties. At Okinawa, two thousand kamikazes led to just under 9,000 Navy dead and wounded, with more dead than wounded. The Japanese had ten thousand kamikaze aircraft alone prepared for Operation Olympic, with a large number of suicide weapons on and under the sea as well.

20. The invasion that never was

Operation Downfall and its components Olympic and Coronet was never approved by the president and was obviously never implemented, the Japanese surrender rendering it moot. After the two atomic bombs and the Soviet invasion, the Japanese surrendered, but not unconditionally, since they negotiated to be able to keep Hirohito on his throne. The argument over whether the invasion of Japan was necessary was present then and remains present when studying the history of the war today. In one area there can be no argument. Had the Olympic phase gone forward as planned in 1945 the casualties would have been horrific, on land and sea, and many Americans and Japanese who survived the war would not have lived to see their families again.

Some argue that the use of the atomic bomb was justified by its removing the need for invading and actually saving hundreds of thousands of Japanese and American lives. Others argue that neither the invasion nor the atomic bombs were necessary. Neither was the sneak attack on Pearl Harbor necessary. Planning for the invasion that never was would not have been necessary had it not been for the military overlords which launched the Pacific War. Their contempt for human life across the Pacific made it necessary. Had Operation Downfall been launched it would have been conducted with the same determination and professionalism demonstrated at places named Guadalcanal, Tarawa, the Philippines, Okinawa, and others too many to list.

Where do we find this stuff? Here are our sources:

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“The Admirals: Nimitz, Halsey, Leahy, and King – The Five Star Admirals Who Won the War at Sea”. Walter R. Borneman. 2012

“The last kamikaze: two Japanese pilots tell how they cheated death”. Justin McCurry, The Guardian. August 11, 2015

“Why We Didn’t Use Poison Gas in World War II”. Barton J. Bernstein, American Heritage Magazine. August/September 1985

“Sakhalin memories: Japanese stranded by war in the USSR”. Daniel Sandford, BBC News. August 3, 2011

“The Final Months of the War with Japan”. Douglas J. MacEachin, Central Intelligence Agency Center for the Study of Intelligence. Online

“The Royal Navy’s Pacific Strike Force”. David Hobbs, Naval History Magazine. February 2013

“Whirlwind: The Air War Against Japan, 1942-1945”. Barrett Tillman. 2011

“PASTEL: Deception in the Invasion of Japan”. Dr. Thomas M. Huber, Combat Studies Institute (pdf). 1988

“MacArthur as Military Commander”. Gavin Merrick Long. 1969

“Olympic versus Ketsu-go”. Jack Bauer and Alvin D. Coox, Marine Corps Gazette. August 1965

“How Japan Got Ready For Suicide”. Richard Halloran, and Special to the New York Times. The New York Times. 1985

“Japanese Mass Suicides”. Nancy Bartlit and Richard Yalman, Atomic Heritage Foundation. July 28, 2016

“The Information War in the Pacific”. Josette H. Williams, Center for the Study of Intelligence. CIA online

“In the Service of the Emperor: Essays on the Imperial Japanese Army”. Edward J. Drea. 1998

“Downfall: The End of the Imperial Japanese Empire”. Richard B. Frank. 1999

“Japan: No Surrender in World War Two”. David Powers, BBC History. February 17, 2011

“The Invasion of Japan: Alternative to the Bomb Downfall”. John Ray Skates. 1994

“The Biggest Decision: Why We Had To Drop The Atomic Bomb”. Robert James Maddox, American Heritage Magazine. May/June 1995

“Memorandum on Ending the Japanese War”. Herbert Hoover, Truman Presidential Library. May 1945