Operation Downfall: The Planned Assault on Japa

The Strategic Situation 1941 – 44
The Air Offensive against Japan
The Evolution of American Planning


Downfall 1 Downfall 2 Downfall 3 The Pacific War had begun with the surprise Japanese attack on Pearl Harbor on 7 December 1941, an attempt by Imperial Japan to destroy the US Pacific Fleet and pave the way for Japanese domination of East Asia and the Pacific. The event had brought the United States into the Second World War and even though the focus of Allied attention had been the defeat of Nazi Germany, the Allies had still committed substantial forces to fighting the Japanese attempt at expanding their Co-Prosperity Sphere. By the late summer of 1945, these forces had managed to battle their way to the very doorstep of Japan itself, despite substantial Japanese garrisons remaining in Southeast Asia, China, Korea, Manchuria and Taiwan. They now contemplated the prospect of having to invade the Japanese Home Islands themselves in order to bring the war to an end. In August however, two atomic weapons became available as part of the Manhattan Project that had begun in June 1942 under the leadership of General Leslie R Groves of the US Army Corps of Engineers. History records that two devices were dropped on Hiroshima and Nagasaki that promptly resulted in the Japanese suing for peace. But what if the Manhattan Project had been delayed, failed, or stuck at a critical point? One alternative open to Allied planners was a conventional invasion of the Japanese Home Islands.

Back in June 1945 before the Trinity test had been conducted, plans for the invasion of the Japanese Home Islands were submitted by the Joint Chiefs of Staff to President Truman for approval under the overall codename of Operation Downfall. Downfall consisted of a two stages. The first stage of the invasion would see a landing on the southern most of the Japanese main Home Islands, Kyushu, under the codename of Operation Olympic, which was scheduled to take place on 1 November 1945. It would provide an advanced staging area for the second phase of the invasion, codenamed Operation Coronet, that would see a landing on the eastern coast of Honshu on 1 March 1946 aimed directly at the Kanto Plain and the capital, Tokyo. Operation Downfall would have involved hundreds of ships, thousands of planes and hundreds of thousands of troops in the largest amphibious assault in history, easily dwarfing the D-Day landings (Operation Overlord) of June 1944.

The Strategic Situation 1941 – 44

Emperor Hirohito's announcement on national radio that the "war effort had not necessarily developed to Japan's advantage" shocked the civilian population more than it did the military. They realised that the war against the United States and the Western Allies had been lost, a confirmation of the feeling that had began with the arrival of American bombers over Japanese cities in mid-1944. The higher military echelons however had foreseen this possibility before the start of the Pacific War, as without a quick victory, Japan's defeat was inevitable.

Although Japan had invaded China in mid-1937 after the Marco Polo Bridge Incident, where Chinese troops had allegedly fired on Japanese soldiers, near Peking (now Beijing), Japan's Greater East Asia War started in earnest on December 1941 due to two intractable and complementary problems, which the Japanese could not solve, without, from their point of view, resorting to arms. Japan itself is relatively poor when it comes to the possession of industrial raw materials and so it was vital for her to be able to guarantee the import of these resources for her industry to continue produce the goods and services vital for a modern industrialised country. Japan feared that as many of the areas that contained these raw materials were in the possession of the United States or the Western Allies (such as France, Britain and the Netherlands) she would gradually become subservient to their will. But in order to guarantee the raw materials on which she depended, Japan would have to free these lands from colonial domination and set up an 'East Asia Co-Prosperity Sphere'. This would necessitate a two-pronged offensive, devised by Japan's premier strategist, Admiral Isoroku Yamamoto. The opening phase would involve a surprise attack on the US naval base at Pearl Harbor, headquarters of the US Pacific Fleet. As Japan's chances of winning a prolonged conflict were small, it was vital that she ensure a quick victory. The destruction of the US Pacific Fleet would enable Japan to launch the second phase of the operation by occupying not only the vital resources areas, such as the Dutch East Indies, Malaya, Burma and the Philippines, but also a large number of island groups that would allow the Japanese to organise an impenetrable defensive barrier ranging from the Kuriles in the north, through the Marshall, Gilbert and Carolina Islands in the Central Pacific, to the Dutch East Indies and Malayan Peninsula in the southwest. It was expected that, faced with the prospect of an enormously costly war to retake this territory, the United States would concede East Asia en masse to the Japanese.

In 1941, the balance of forces in the Pacific favoured a rapid Japanese victory. Although in most types of surface combatants, the Imperial navy could be balanced by the combined forces of the United States and Western Allies (including Britain, Australia and the Netherlands), Japan had the advantage in aircraft carriers, having twelve such ships that could project almost 700 aircraft, compared to the United States' three aircraft carriers with only 280 aircraft. This advantage reigned supreme in the first six months of the war and enabled Japan to inflict the most disastrous defeat in American naval history as well as wage and win the most stunning amphibious campaign conducted up until that point. It all began on 7 December 1941 when, at a cost of twenty-nine planes and fifty-five men, the strike on Pearl Harbor killed almost 2,500 personnel, sunk five battleships and destroyed over 200 planes. Immediately afterwards, some ten Japanese infantry divisions swept through most of Southeast Asia in a series of rapid assaults, including Wake Island (23 December), Hong Kong (Christmas Day), Malaya and Singapore (February), the Dutch East Indies and Burma (March) and the Philippines (May). Never before in military history had so much territory been taken so quickly and at so little cost. The role and effectiveness of the aircraft carrier strike force had been demonstrated and set the pattern of the remainder of the campaign. However, while the Japanese strike at Pearl Harbor was a serious blow, the Japanese had failed to catch the American carriers there and so the ships eventually became the nucleus of the force that was to pierce the defensive perimeter of the Japanese Empire. In the protracted war that was to follow, American industrial muscle combined with a determination to see Japan militarily defeated, would make Japan's defeat inevitable, a point that was made perfectly clear with the Doolittle raid on Tokyo on 18 April 1942, an act that stung the Japanese who thought they would never see the underside of an enemy bomber.

Despite the Doolittle raid, the successes of late 1941 / early 1942 meant that Japanese morale was very high and with the apparent weakness of the Allied powers, Japan sought to extend her defensive perimeter south by attempting to occupy the islands bordering the Coral Sea (including New Guinea and the Solomon Islands) and cut the communications route between the USA and Australia, thus preventing the continent from being used as a staging base for an Allied counteroffensive. On 7 May, an American task force centred on the carriers Yorktown and Lexington intercepted a Japanese amphibious force bound for Port Moresby on New Guinea. In the ensuing two-day battle, the Japanese lost the carrier Shoho while the Americans lost the Lexington. The Japanese were forced to turn back, nursing a second carrier that had been damaged while the Yorktown limped back to Pearl Harbor, to be repaired in time for the next major battle, Midway.

Following the minor setback in the Coral Sea, the Japanese planned to destroy the remaining American naval strength by attacking the island of Midway, a key location in the American air-search-and-patrol triangle of Midway, Pearl Harbour and the Aleutian Islands. This would draw out the remaining American surface fleet, and once destroyed, the Japanese could then strike at Hawaii, the Panama Canal and even the West Coast of the United States itself, which would be aimed at 'persuading' the USA into a negotiated settlement. In late May, Yamamoto advanced on the island of Midway with the largest fleet that had up until then set sail: ten battleships, eight carriers, twenty-four cruisers, fifteen submarines and seventy destroyers – in all a force of over 185 ships along with 685 naval aircraft. They outnumbered the American fleet under Admiral Chester Nimitz by three-to-one but the Americans had the advantage of having partially broken the Japanese naval code, knowing what sort of force the Japanese had and where they would be approaching from. The Japanese submarines arrived on station too late to catch the American task force and with some additional good luck (the actual reconnaissance aircraft that was to patrol the area where the American carriers would be, arrived late due to engine problems) the Americans managed to sink four carriers (three during the battle and one during the retreat) for a loss of one (the Yorktown). Japan would never recover from the losses inflicted on them at Midway (half her carriers, over a hundred of the most experienced pilots and around 280 planes) and lost the ability to wage an aggressive war, which meant an extended war of attrition that Japan would ultimately loose, given American industrial superiority. By June 1942, American shipyards had launched twenty-four flattops (six heavy, two light and sixteen escort carriers) and so even by the sixth month of the war, Japan was now facing almost certain defeat.

In August 1942, the American counteroffensive started at Guadalcanal, an island in the Solomons chain. The issue of contention was an incomplete airstrip, named by the Americans ‘Henderson’ Field, after Major Loften Henderson, a Marine Corps pilot killed during the Battle of Midway. Henderson Field was the only land facility between the main Japanese base at Rabaul (some 650 miles northwest of the island) and the US naval station at Espiritu Santo (over 600 miles southeast of the island), whoever held the airstrip could dominate the island. The US 1st Marine Division took the airstrip shortly after it landed with virtually no casualties. However, the Japanese spent the next six months trying to recapture it, rather than develop other airfields in the vicinity to provide them with airpower in the local area. It cost the Japanese some 20,000 troops in futile banzai style charges against an American perimeter that had substantial firepower in the defence. The Japanese Navy managed a slight victory in the waters off the island due to superior training in night actions but this could not make up for the massive superiority in American warship construction. These tactics would push the Japanese fatality rate from just over 100,000 to over a million by the end of the war.

In February 1943, the Japanese managed to evacuate over 12,000 troops from under the noses of the American forces on Guadalcanal, which was quite a triumph. Unfortunately, while successful evacuations are helpful in not losing a war, as Churchill said, ‘Wars are not won by evacuations’. In late 1942, American and Australian troops had crossed the mountainous middle of New Guinea and succeeded in defeating the Japanese in a number of sharp engagements and in March 1943, Allied aircraft had turned back a Japanese convoy in the Bismarck Sea that was attempting to reinforce Japanese forces on New Guinea. Combined with this, Allied forces advanced up the New Guinea coast in a series of amphibious jumps and Allied submarines and aircraft managed to successfully interdict Japanese reinforcement and resupply efforts, sinking some two-and-a-half million tons of merchant shipping by November 1943. By mid-1944 this figure had doubled and the remaining three million tons found itself hard pressed to supply even the minimum needs of the home islands and island garrisons that were soon to find themselves exposed to American counterattacks. Even by early 1943, the writing on the wall was plainly visible for all to see, which accounted for the self-stage managed death of Japan’s leading strategist. In April 1943, Yamamoto leaked the details of his visit to the Solomons in a code that was known to have been broken by the Americans. The Americans initiated Operation Vengeance, a military assassination given the presidential go-ahead. On 18 April 1943 a squadron of American Lockheed Lightning aircraft intercepted Yamamoto’s flight. In this way, he gained immortality and escaped the ordeal that was about to overtake his country and its armed forces. The news of his death generated a strong degree of fatalism among every Japanese in every theatre. In May 1943, 11,000 American troops descended on the 2,500 troops in the Japanese garrison on the Aleutian Islands. The commander used the last 1,000 troops in a banzai charge in which many Japanese blew themselves up with hand grenades once they had reached the American lines.

In November 1943, American forces advanced in the Central Pacific, invading the Gilbert Islands with a fleet consisting of nineteen carriers, twelve battleships, fourteen cruisers and sixty-six destroyers. The Gilberts (the principle targets of which were the Makin and Tarawa Atolls) were secured with around 1,000 Americans killed as opposed to 5,300 Japanese killed. The Americans took a grand total of seventeen Japanese and 129 Koreans prisoner. It was gradually becoming apparent that the Japanese would opt for death over capture or surrender in future engagements. The United States next struck the Eniwetok and Kwajalein Atolls in the Marshall Islands, very close to the centre of the Japanese outer defence ring. The American landings pitted over 50,000 assault troops against 11,000 Japanese defenders – only some 300 living to be taken into captivity. During this attack, American aircraft launched an 800 plane attack on the Japanese base at Truk (Caroline Islands), destroying some 300 Japanese planes, sinking twenty-six merchant ships and six combat surface vessels. A similar raid was launched against the Mariana Islands a week later. Between March and June 1944, the Americans prepared to seize the Marianas from which the new B-29 Superfortresses could strike the Japanese Home Islands thus destroying their capacity to wage war. Directly before the Americans landed on the Marianas, the Battle of the Philippine Sea saw Admiral Nimitz engage the remnants of the Imperial Fleet (four battleships, nine carriers, seven cruisers and thirty-four destroyers) with a vastly superior force of fourteen battleships, fourteen cruisers, eighty-two destroyers and twenty-six carriers. The last attempt by the Japanese to stem the American advance by seeking a decisive naval engagement had failed.

Saipan was the first target in the Marianas and was attacked in early July 1944 by some 67,500 American troops. Some thirty thousand Japanese soldiers and sailors died in its defence, with another 15,000 Japanese civilians choosing suicide over capture. However, for the first time significant numbers of Japanese fell into captivity on Saipan – some 920 troops and 10,000 civilians. Next came Tinian and Guam – Guam was secured by 10 August 1944 with an assault force of 55,000 US troops against 20,000 Japanese, of whom only some 1,500 would surrender, while 15,500 US Marines attacked Tinian in late July after an incredible three-day pre-invasion bombardment that included the first use of napalm. That island was secured a week later, the Marines having suffered a mere 389 killed as against 5,000 Japanese. It would be from Tinian that the Enola Gay would fly to deliver its deadly cargo on Hiroshima.

Another 65,000 Japanese sailors and soldiers would die at the Battle of the Leyte Gulf and on Leyte itself. Overall, a quarter-of-a-million Japanese would be lost during the desperate SHO (Victory) operations in the Philippines. In September 1944, the 1st Marine Division attacked the island of Peleliu, part of the Palau Island group, as part of Operation Stalemate II. The operation had been delayed due to the time taken to secure the Mariana Islands and saw a major change in tactics on the part of the Japanese Commander, Lt General Sadao Inoue. No longer would the Japanese plan to defend the landing beaches in strength, where the weight of American firepower could be brought to bear. They would lightly defend the beach but construct a defence in depth, utilising the terrain to best advantage, while conducting small-scale local counterattacks instead of the mass banzai charges that were in the main, costly failures. The plan was to bleed the Americans white. After landing on the 15 September 1944, the battle raged for seventy-three days with the 81st Infantry Division taking over from the Marines as their casualties rose to staggering proportions. The island was finally secured by the end of November, although Japanese troops fought on until the end of the war, with some only surrendering in 1947. The Marines suffered over 6,700 casualties (1,300 killed), while the Army suffered some 3,000 casualties (468 killed). The new tactics had been proved a success and the word went out to all Japanese formations to adopt them. A similar pattern would be followed on Iwo Jima (Operation Detachment) and Okinawa (Operation Iceberg). On Iwo Jima, the three Marine divisions of the V Amphibious Corps battled around 21,000 Japanese defenders under Lt General Tadamichi Kuribayashi for some thirty-five days after the landing on 19 February 1945. Instead of the wasteful banzai charges seen on Guadalcanal, Kuribayshi concentrated on night infiltration tactics and small localised counterattacks to recapture key terrain. The Americans suffered some 26,000 casualties (6,766 killed) while the Japanese suffered just over 21,000 casualties, almost all of them fatalities. What was supposed to be a short, sharp campaign turned into a major slugfest, the most costly battle in the history of the US Marine Corps and had a sobering effect on the planning for Operation Olympic.

At the same time, the devastating air assault on Japan threatened to throw her back to the Dark Ages but despite the enormous destruction of residential, commercial and industrial property, as well as the continuing effects of the American air and naval blockade, the Japanese continued to carry on with their preparations for the eventual invasion of the Home Islands. Weapons production for the period between April and September was scheduled to produce 500,000 rifles, 10,000 machine guns, 5,000 mortar and artillery pieces and six hundred antiaircraft guns for use in the final battle. Slated for use against the American fleet were 6,000 crash attack boats and 2,000 midget submarines and piloted torpedoes. Strenuous efforts were made to continue with the aircraft production programme, despite the American effort against Nagoya, with around 16,000 aircraft scheduled for completion by September 1945. About a quarter of these however, were designated to take part in the Army's Ten-Go Operation in the final stages of the Okinawa Campaign.

This was followed by the battle for Okinawa, the largest of the Ryukyu Island chain, which started on 1 April 1945 with the landing of the US Tenth Army, consisting of the III Amphibious and XXIV Corps. This was the largest joint operation in the Pacific and because the terrain on Okinawa strongly resembled that of Kyushu, it provides the best indicator as to how the battle for Kyushu might have gone, had it been executed in November 1945. There are differences however, as the Japanese objectives in the Okinawa Campaign were different to those intended for the fighting on Kyushu. The battle for Okinawa was conducted as another delaying action during which the Thirty-Second Army attempted to buy time for the preparations on Kyushu to be completed. The campaign on Kyushu would have been the first of two last stands (the second coming on Honshu during Operation Coronet). Lt General Mitsuru Ushijima, commander of the Thirty-Second Army, planned to make the Americans pay as dearly as possible for their victory on Okinawa and realising that no beach defence between Tarawa and Iwo Jima had succeeded in holding the landing area, deployed his troops inland in the southern half of the island along three natural defence lines that had been fortified by the defenders. This tactic spared the Japanese the immediate consequences of the increasingly effective and efficient American naval gunfire support, which happened to be the heaviest executed during the Pacific War up to that point. Additionally, the Japanese hoped that the onslaught of the Kamikaze force at Okinawa might prevent an American beachhead from being established. While it failed to achieve this, the Kikusui (Floating Chrysanthemums) air offensive inflicted the highest material and personnel loss on the US Navy during the Pacific War. Between the 6 April and 22 June, over 1,900 Japanese tokko aircraft were committed against the 1,200-ship US fleet. The US Navy suffered almost 10,000 casualties, had thirty-six ships sunk, another 368 damaged with some forty-three of these being so badly damaged that they were scrapped. From these results, the Japanese took hope that they might be able to repel the American invasion of the Home Islands and planned to deploy around 5,000 tokko aircraft against the American fleet. The fighting on Okinawa proved to be the most tenacious the Americans would encounter during the Pacific Campaign as each of the three defence lines were firmly held and as defensive positions became untenable, they would withdraw the defending forces and leave behind small units to sacrifice themselves in holding up the American advance. Natural and man-made caves were exploited to the full, most being fortified into pillboxes, gun emplacements, strongpoints and bunkers, utilising automatic weapons and light artillery pieces. These positions would be covered by numerous trenches, firing pits and foxholes. Most of these caves proved invulnerable to anything but the heaviest naval gunfire conducted at almost point blank range, and so the Americans had to use what was termed 'blowtorch and corkscrew' tactics, developed in the Philippines and refined on Iwo Jima. The blowtorch was a high-powered flamethrower inside the 75mm gun of a Sherman tank (nicknamed 'Zippos') that would be used to saturate the cave entrances with a stream of flame while infantry would move round to place demolition charges to seal up the caves and any Japanese still inside. The fighting raged for eighty-two days and it was only the longer fought Philippine Campaign where greater casualties were sustained. In total, the Americans suffered around 51,000 casualties with just over 12,500 killed and lost 763 aircraft. The Japanese forces numbered just over 100,000 on Okinawa and while a huge number were killed in the battle itself, the mopping up taking until November 1945, for the first time significant numbers of Japanese military personnel surrendered after the battle, the number rising to over 16,000 by the end of the year.

The United States now possessed a base just over 500km (320 miles) southwest of Kyushu. A colossal construction project began utilising some 87,000 construction troops from the US Army, Navy and Royal Engineers to build some 22 airfields to accommodate the Eighth Air Force deploying from Europe, as well as Marine and Navy air units while Navy and Marine airfields were established at Awase and Chimu on Okinawa and Plumb Field on Ie Shima. The Naval Operating Base, Okinawa was established at Baten Ko on the southern end of Buckner Bay (the renamed Nakagusuku Wan) to control the port facilities at Naha, Chimu Wan, Nago Wan and Katchin Hanto. The island gradually developed into a major staging base for the Army and Marine units that were slated to participate in the invasion of Japan. Two extremely powerful typhoons in September and October caused serious damage and the relocation of a number of port facilities. The main naval base was moved from Baten Ko to the southeast end of the Katchin Peninsula to what was, and is, still known as White Beach. The deployment of the two atomic bombs eventually made the build-up on Okinawa unnecessary, but both the Korean and Vietnam Wars saw the island play an important role as a logistics base for the US Armed Forces.

The Air Offensive against Japan

As the Allied forces were approaching Japan, small numbers of B-29 Superfortresses had started to operate from the Chengtu region of China in June 1944 as part of Operation Matterhorn. The B-29 was the largest bomber used operationally in substantial numbers during the Second World War, carrying a 16,000lbs payload a distance of up to 4,000 miles. This effort had little appreciable impact upon Japan’s war economy as the number of bombers involved had been small as the logistics of mounting an air offensive from central China had proven very difficult to overcome with the planes, spares, fuel, munitions, food, oil and engines all had to circumvent a 16,000 mile supply route from Casablanca to India and from there, over the Himalayas to the airbases. In November 1944, the 21st Bomber Command started to operate from the recently captured bases in Guam, Saipan and Tinian (the Mariana Islands) and while the weather between the Marianas and the Japanese Home Islands was frequently atrocious, the bases were easily resupplied and so in January 1945, the 20th Bomber Command under General Curtis LeMay left China to join the 21st in the Marianas where LeMay was to assume overall command.

Up until that point, the B-29s had been using daytime, high-level precision bombing to attack the Tokyo-Osaka-Nagoya region of Japan where some 80 percent of Japan’s combat aircraft were being produced. Results so far had been poor and the daylight raids had encountered heavy fighter resistance with casualties rising to six percent of the force committed during February 1945. When LeMay took over, he began to experiment with nighttime raids using incendiary munitions in order to improve bombing effectiveness. This switch in tactics reaped vast rewards, as Japan proved extremely vulnerable to night attack as she lacked an adequate number of night fighters and her antiaircraft guns were manually controlled, rather than radar controlled. Also, only by incendiary attacks could the Americans hope to destroy the Japanese war industry, which by that time had been largely dispersed into private homes, shops and businesses in the major urban areas. The first major attack came on the night of 9 / 10 March 1945 when 334 planes that had been stripped of weapons and carried only the minimum amount of fuel to maximise their bomb load, bombed the city. Each carried almost five tons of M-69 incendiary bombs, which were dropped onto the Asakusa Ward in Tokyo, probably the most densely populated area on the planet at an average of 130,000 residents per square mile. Within minutes, a man-made hell appeared on the ground as the flames were fanned by a strong wind, raising temperatures to over 1,800 °F. The city's residents tried to escape by jumping into rivers, reservoirs, lakes and pools but many were killed as they breathed the super-heated air that accompanied the conflagration. Some 9,000 feet above the target the American aircrews were sickened by the stench of burnt flesh.

The Tokyo firebombing was one of the single most destructive attacks in history. Over 80,000 people were killed (compared to anywhere between 35,000 and 135,000 in Dresden, the city being packed with refugees fleeing the Red Army making estimation of the exact numbers of casualties almost impossible) and almost twice that number were injured, over 250,000 buildings were destroyed leaving another million Japanese homeless with almost sixteen square miles of city being devastated. The results spoke for themselves, with the Americans only loosing some fourteen B-29s. The conclusion was that it might be possible to bring Japan to her knees by using the technique of firebombing rather than risking a single GI in a conventional invasion. Japan would be put to the torch:

In ten days, American bombers had dropped around 10,000 tons of bombs and levelled over twenty-nine square miles from the hearts of the major Japanese urban and industrial areas. The firebombing continued until August when the two atomic bombs became available. The raids had become easier after the seizure of the islands of Iwo Jima and Okinawa in February and April 1945 that had meant fighter cover could now be furnished and emergency landing facilities were now available. These factors reduced American bomber losses still further, as did the use of carrier airpower to hit shipping, port and industrial targets around Japan's coasts.

Many of the major metropolitan areas had been evacuated by June 1945, including some 4.5 million people from the Tokyo – Yokohama – Kawasaki area and so the casualties for each raid declined but the Japanese had suffered at least 125,000 killed and some 250,000 injured, over 1 million buildings had been destroyed and some 5 million people made homeless. Tokyo, which had absorbed over 11,000 tons of bombs, had been reduced to half its pre-war size. Despite all this however, there seemed to be no hint coming from the Imperial Palace (that had been carefully spared) that the Japanese might surrender. The majority of Japanese officials had long recognised that it had been a very risky strategy to go to war with the United States, unless Japan could have gained a massive strategic advantage very early on, something they had failed to accomplish, despite the success of Pearl Harbor. After the battle of Midway, the Pacific Campaign had gradually deteriorated until Japan was now facing a situation where she should surrender, and surrender quickly, but these officials could not admit to each other that Japan was truly defeated. Ever since the successful 'blitzkrieg' campaign of late 1941 to early 1942, Hirohito and the Japanese Government had been keen to conclude the war with a favourable peace settlement and had pursued a number of such avenues towards a negotiated peace settlement but by January 1943, they had all become dead-ends with the Allied insistence of unconditional surrender. By the summer of 1945, a single issue stopped the Japanese from surrendering – they sought a pledge form the Allies that they would allow Japan to retain the imperial governmental system. As it happens, the Americans were not overly opposed to this at all as they needed the Emperor's cooperation in the immediate post-war period when Japan would be occupied. They also wondered if the Emperor was in fact merely a figurehead and so would have little trouble leaving his (presumably) symbolic powers intact. Had the two nations been able to communicate relatively freely and openly, what was to happen next might not have happened at all and two major urban areas and tens of thousands of lives been saved. Unfortunately the Japanese entrusted their messages to Soviet diplomats, who stood to gain large amounts of territory if Japan suffered an Allied invasion and so discreetly withheld news of Japan's willingness to surrender as Soviet forces were being moved from Central Europe to the Far East.

Following the (apparent) failure to give an answer to the Potsdam Declaration of 26 July 1945, which warned of 'prompt and utter destruction' unless Japan surrendered, two atomic devices were deployed and used. The first controlled nuclear reaction had occurred under Stagg Field in December 1942, which was followed by the successful detonation of a test weapon (codenamed 'Gadget') in the desert of New Mexico at the Trinity test site on 16 July 1945. With this test, the United States knew that these weapons were of an awesomely destructive power. The first weapon (codenamed 'Little Boy'), which was a Uranium bomb, exploded over the Japanese city of Hiroshima at 08.15 on 6 August 1945. Of the 245,000 inhabitants, over 64,000 died instantly when the bomb exploded, creating an artificial sun with a surface temperature of 3 – 4,000 ?C near the Aioi Bridge. Over 26,000 died in the following days, weeks and months from blast injuries, burns and cancers from the neutron and gamma radiation. The second weapon (codenamed 'Fat Man') was a Plutonium bomb, and detonated over the city of Nagasaki at 10.58 on 9 August 1945. Nagasaki was a secondary target and was struck as cloud cover had hidden the original target of Kokura. The Japanese promptly surrendered on 14 August 1945 with the surrender ceremony taking place onboard the USS Missouri anchored in Tokyo Bay on 2 September 1945.

The Evolution of American Planning

Between the World Wars, American naval planners had assumed that any war in the Pacific would be mainly a naval one, with the Army's role to hold static defence positions (such as island bases). The issue would be decided between the two grand fleets and once the Japanese had been beaten or its navy forced to retire, the USA would institute a naval blockade. Such a policy was quite sensible, as Japan was an island nation and was very limited in the amount of raw materials it possessed (similar to Britain, although Britain had substantial industrial resources such as coal and iron). It was therefore vulnerable over the long sea lanes with which it imported and exported goods and materials, especially after it had created its Empire. Indeed, for the first two years of the war, American planners held every hope that the Japanese would eventually be brought to its knees by a combination of naval blockade and aerial bombardment. Few, especially in 1942, could see the need for an invasion of the Home Islands, particularly as the bulk of Japan's forces were deployed throughout the Empire, on Formosa, in China and in the Central and South Pacific.

At the Casablanca Conference in January 1943, the Combined Chiefs decided to defeat Japan using tactics that would be effective against the British Isles, that is, blockade, bombing and assault. To effectively institute this strategy, the Allies would have to destroy the Japanese Fleet and take control of a series of bases that would lead to the Home Islands, from where the US Navy would be able to sever the communications links across the Sea of Japan. Even then, it was not guaranteed to force Japan into submission, even with the addition of an intense strategic bombing campaign, or if it did, might take a couple of years to bring results. Despite this, undertaking an invasion was to be considered only as a last resort, as planners recognised that the Japanese Army fought ferociously, the islands generally had rugged terrain and poor roads and the ports would be heavily defended. If such an invasion was to prove necessary, then Kyushu and Tokyo Bay were the most likely invasion sites.

As the war in the Pacific entered its fourth year, Admiral Ernest J King was promoting the plan, codenamed Operation Causeway, to invade Formosa. This island, it was argued, would provide better basing facilities for maintaining the blockade of Japan than Luzon. During the arguments for and against an operation aimed at Formosa, King maintained that a blockade, supplemented by aerial bombardment could force the Japanese to surrender without the need for an invasion. While an attack on Formosa would be costly (it had a substantial garrison) it would ultimately save lives if it could contribute to avoiding a direct invasion of the Home Islands. Despite this, when the Combined Chiefs met for the Octagon Conference in September 1944 (just before the US Marines attacked Peleliu), they expanded the strategic goal of the war in the Pacific to include seizing objectives in 'the industrial heart of Japan' and in November 1944, the US Joint Chiefs of Staff cautiously approved a plan for the invasion of Kyushu in September 1945. Even though King and Admiral William D Leahy had to acquiesce to these decisions, they never agreed that an invasion of Japan would have been inevitable.

By late 1944, the Allies had agreed that the goal would be to force the unconditional surrender of the Axis Powers (Germany and Japan) but could naval blockade and aerial bombardment produce such a result, and within twelve months of the defeat of Germany (decided at the Quadrant Conference at Quebec in 1943)? Also, large ground forces had been built up (with more available once Germany had been defeated) in the Pacific and inter-service rivalry and political pressure back home would mean they would have to be used somewhere. Would they be able to stand idle for many months while the blockade and bombardment strategy proceeded? King finally agreed that invasion planning was a necessity but saw it only as a contingency, with the objective being additional air and naval bases with which to tighten the blockade and intensify the bombing around Japan. This strategy is exactly what the Japanese feared. Lt Col Michinori Ureshino was the staff officer for shipping at Imperial general Headquarters from 1943 until the end of the war. Like his American counterparts, he saw air and naval power as the key to Japan's defeat. By mid-1945, he feared that Japan's seaborne transport was coming to a near complete-paralysis as the volume of tonnage had dropped from 6.3 million tons at the start of the war, to 1.18 million tons in April 1945, to 800,000 in June. By the late autumn, he estimated that there would be nothing left. This would have dire consequences, not only as regards the import of food and raw materials from abroad, but the transport of those materials by means of coastal shipping, which was very important to the Japanese economy (even Britain with its extensive railway network still used coastal shipping). Its collapse would have massive implications for the Japanese population.

Against this claimed superiority by the US Navy as to the role of a naval blockade, came the US Army Air Force (formerly the US Army Air Corps) and its belief in the role of airpower in securing victory. The service had wanted independence from the Army for a while and their view of airpower centred on strategic bombing, not the ground support role that they feared would be forced upon them. Of course, they failed to gain independence but had managed to achieve quite a degree of autonomy nonetheless. The Army Air Force supported Admiral Chester Nimitz's drive through the Central Pacific rather than General Douglas MacArthur's South West Pacific drive, as in Nimitz's path lay the Marianas, which we have seen, were converted to B-29 bomber bases, from where they could reach Tokyo and all the major industrial cities. Iwo Jima was taken at their behest to provide the bombers with an auxiliary strip on which damaged aircraft could land – it also denied the Japanese an advanced outpost with which to warn the mainland of attack. As well as the bombing of Japanese cities (that changed from precision bombing to massed low-level incendiary bombing) the Twentieth Air Force undertook aerial mining to enhance the blockade of Japan, under pressure from the US Navy. Although the campaign started modestly, it soon gained momentum and proved very effective – by June, many ports had been abandoned and many ships were unable to move.

General Henry 'Hap' Arnold and other air force commanders denied that there had been a discrete strategy (in league with the Navy) to achieve victory by purely bombing and blockading, or any overt cooperation with the Navy – everything was done as part of an overall, linked strategy of bombing, blockading and invasion. If Japan surrendered before 1 November 1945, all well and good. If not, then the invasion of southern Kyushu (Olympic) would commence as planned, to provide additional air and naval bases to tighten the blockade and intensify the air bombardment, as well as provide an additional staging area for the invasion of Honshu, scheduled for 1 March 1946 (Coronet) if that proved necessary. The official Air Force historians contend that the targeting criteria set forth by the Air Staff were made on the assumption that an invasion would prove necessary – they had digested the lessons from the bomber campaign in Europe and felt that it was very unlikely that air power alone would achieve victory. There was however, still a degree of inter and intra-service rivalry and self-interest as the Air Force wanted air power to prove decisive as a useful prerequisite for independence and to justify the enormous amount of resources and manpower devoted to it. The results of the bombing campaign in Europe had proven less than decisive (important though the campaign had been) and the campaign over Japan would be their last chance.

As the debate between the services (as well as personalities) on how best to defeat Japan gathered pace, Admiral King and the Navy planners pushed for an encirclement strategy not unlike Churchill's European strategy of slicing off discrete parts of German-occupied Europe one bit at a time. General George C Marshall and the Army favoured a direct thrust on the Japanese Home Islands. By mid-1944 the Allies were still operating with a strategic concept that saw an invasion as a last resort, something that was more than a year old, but Marshall pressed for a more explicit strategy, something that included invasion, and so in July 1944, the Joint Chiefs approved a report from their Joint Planning Staff (JPS 924, 7 July 1944) that the Japanese ability to wage war and will to resist would be lowered by continuing air bombardment and naval blockade but an invasion to seize objectives on the Japanese Home Islands would be carried out as and when necessary. While this hardly made an invasion inevitable, on 1 April 1945 the battle for Okinawa started in earnest and the Joint Chiefs were no longer able to evade the question of an invasion. Before the struggle with Japan could be settled, another battle, between Marshall and King – the Army and the Navy – had to be settled in Washington DC. This struggle took place in April and May 1945 and hinged on two important considerations: should preparations for the invasion of Kyushu be started so as to allow for a 1 November 1945 start date and secondly, if this was to be the case, who would command it?

On 3 April 1945, the Joint Chiefs issued directives (JCS 1259/4 and 1259/5, 3 April 1945) to MacArthur and Nimitz to begin planning for Operations Olympic and Coronet and gave a target date of 1 December 1945 for Olympic and 1 March 1945 for Corornet, causing both MacArthur and Nimitz to point out (in JCS 1331/1, 30 April 1945) that a target date as late as December might subject the invasion to uncertain weather conditions which could force it back to the spring of the following year, thus delaying the end of the war. King and the Navy planners however, did not preclude interim operations between the end of the Okinawa campaign and the assault on Kyushu. King favoured securing more bases around Japan to tighten the noose, whereas Marshall and the Army favoured a massive direct assault on Kyushu. The first step in King's strategy of encirclement, was Operation Longtom, the seizure of a lodgement on the Chusan-Ningpo archipelago near Shanghai, after which additional lodgements on the Shantung peninsula, Korea, Quelpart and Tsushima Islands would provide additional air and naval bases with which to intensify the blockade and bombardment of Japan. Nimitz had put together a plan for Longtom by 18 April 1945 and like King, believed that any hasty attack on Japan would produce unacceptable casualties and so additional encircling operations should be conducted. Meanwhile, on 28 March 1945, General Thomas Handy (Deputy Chief of Staff) had sent a memo to Marshal outlining what he believed to be the main points of the Navy's plan, mainly that there should be additional operations conducted to intensify the blockade and bombardment of Japan but to also cut it off completely from the Asian mainland. His aim was to provide Marshall with information with which to counter King's arguments – mainly that the encircling operations would take up valuable time and cost as much in men and material as Olympic would cost, while still having Olympic to undertake at the end of it. Furthermore, Handy was uncertain as to the suitability of much of the terrain for the building of air and naval bases.

On 12 April, Marshall communicated to MacArthur the essence of the two opposing views. The arguments for a peripheral strategy was the high casualties involved in a direct landing on Japanese soil, the necessity to continue to degrade Japanese airpower, cutting off Japan from reinforcements on the Asian mainland and the possibility that it might provide time for the blockade – bombardment strategy to produce a Japanese surrender without an invasion. The arguments for a direct assault (as soon as possible after the Okinawa campaign) were that Japanese air and naval power would be weak enough by the end of 1945 anyway, the Japanese would be unable to bring enough troops from the mainland to significantly affect the balance of combat power, Soviet entry would have a demoralising effect and a peripheral strategy would require as many troops and produce as many casualties as an invasion. Marshall then asked if MacArthur had any thoughts on the debate. MacArthur's response read like an answer to a Staff College exam question. To MacArthur, there were three possible courses of action:

The first alternative would bring to bear a greater amount of American airpower, cut off Japanese communications with the mainland and probably allow Kyushu to be bypassed in favour of a direct assault on Honshu. It would however, deploy American combat forces off the main line of advance without the benefit of better short range air cover than that already available from Okinawa, they would tie up a large percentage of the combat forces available in the Pacific that may very well necessitate the redeployment of additional combat forces from Europe and lodgements on the Chinese coast may draw American forces into an involvement on the Asian mainland. Finally a series of peripheral operations would lead to additional casualties before the main assault had even begun. MacArthur viewed bombardment and blockade as the worst situation as it might prolong the war for a substantial amount of time, and the evidence so far as to airpower's ability to subdue an enemy alone, was not very positive, given what had happened in Europe. Rather unsurprisingly, MacArthur came down in favour of an assault on Kyushu as it would permit the USA to apply the full strength of its available forces to achieving the desired objective. In the meanwhile, while Marshall had not specifically asked for Nimitz's advice, he received the Admiral's thoughts as Nimitz had received an information copy of Marshall's request to MacArthur. He too favoured an assault on Kyushu but warned that bases, shipping and supplies (logistics in other words) were critical factors and that the USA should follow a peripheral strategy until preparations had been completed for the Kyushu assault that would ensure success. Additionally, a lodgement on the Chinese coast would encourage the Soviet Union into the war and open an all-season supply route to them. Added to this, the Joint Intelligence Staff entered the fray with a report entitled 'Defeat of Japan by Blockade and Bombardment' (JIS 141/3, 14 April 1945) which summarised that such tactics would render the Imperial Japanese Navy impotent, destroy its Air Force, reduce the combat ability of the Army to a few months and sap the will of the Japanese people to continue to resist. But the nub of the question remained – how long would it take? Estimates varied from the end of 1945 to the latter part of 1946.

Even so, Marshall was working with Henry L Stimpson and Grew to try and find some way to soften the demand for unconditional surrender that might negate the need for a costly assault on the Japanese Home islands. He commissioned a number of studies from the committees attached to the Joint Chiefs of Staff that addressed the military implications of the demand for unconditional surrender. All the studies supported backing away from the condition of unconditional surrender. The Joint Intelligence Staff report indicated that it was very possible that Japan would admit defeat by the autumn of 1945 but it was extremely unlikely that they would accept unconditional surrender – indeed they may not even be able to comprehend the term. The report came to three overall conclusions. Firstly, the term should be explained to the Japanese as meaning complete defeat, not national extinction. Secondly, the Japanese military and the civilian population would only accept a move to surrender with authority from the Emperor. Thirdly, stability in an occupied Japan could only be assured if the Government of Japan was supported by the Emperor as well as the Allied control authority. They also looked at how an adherence to the condition of unconditional surrender would affect the strategy of bombardment and blockade and concluded that it could cause the war to go on for a very long time indeed, perhaps even several years. Such a softening of attitude as regards unconditional surrender could produce a Japanese surrender in late 1945 or early 1946. However, the State Department still opposed any move away from this policy and so the Joint Chiefs were left with little alternative to a strategy of invasion.

As the two sides pressed their respective strategies (encirclement vs. direct assault), the other issue remained to be resolved – who would command the invasion itself? From the earliest days of the Pacific Campaign, the Army and Navy had been unable to agree on a single overall commander for the Pacific and so the Joint Chiefs imposed a compromise solution based around area commands. The two largest and most important were MacArthur's Southwest Pacific Area and Nimitz's Central Pacific Area. Each area had its own naval, air and ground forces but as both Nimitz and MacArthur advanced on Japan, these separate areas made less and less sense, and a combined invasion of the Home Islands would require much more closely coordinated efforts than had been seen up to now (Okinawa included). In recognition of this, the command directives issued on 3 April 1945 by the Joint Chiefs also looked to start a major realignment of forces in preparation for the invasion. MacArthur became Commander-in-Chief, Army Forces Pacific (CINCAFPAC), the direct counterpart to Nimitz, who was Commander-in-Chief, Pacific Fleet (CINCPACFLT). The intent was to realign all Army forces under MacArthur but following the previous pattern the Navy wished to create another command area for the invasion, under a Commander-in-Chief, Japan (CINCJAPA). Eventually, King relented on this, but it is interesting that the command directive that was supposed to simplify things actually gave rise to another round of squabbling and inter-service rivalry.

By the end of April, the Joint Planning Staff had released a report entitled 'Pacific Strategy' (JCS 924/15, 25 April 1945) which looked at the way the campaign might unfold in the remainder of 1945, especially the invasion of the Home Islands and agreed that directives should be issued for the commanders in the Pacific to proceed with an invasion of the Home Islands. However, the controversy over command continued to rumble on – the main issue being the precise wording as to the missions assigned to MacArthur and Nimitz in the proposed directives. King issued the first challenge by proposing a directive that would give the primary role to the Navy in a strongly blockade and bombardment strategy that would see MacArthur's ground forces conduct a limited invasion, to secure air and naval bases for the assault on the Tokyo Plain if that proved necessary. Unsurprisingly, MacArthur and Marshall objected to this and presented their own plan that would see MacArthur in control of the campaign, with control of the amphibious phase being exercised through the appropriate naval commander. The Navy in turn objected to Nimitz's subordination to MacArthur and offered an alternative, one that saw Nimitz coordinate his strategy with MacArthur. Navy planners saw Olympic as a two-phase operation – the first phase being an amphibious assault (under Nimitz) followed by a land campaign (under MacArthur). Army planners however, viewed it as one continuous campaign that should be under the control of a single commander. King and Marshall finally reached an impasse in Washington and presented the problem to the two Pacific commanders. Nimitz and MacArthur met in Manila in mid-May, at the same time the Joint Planning Staff issued its recommendations as to how to solve the command issue, entitled ‘Directive for Operation Olympic’ (JCS 1331/2, 14 May 1945). The two had generally agreed on matters pertaining to the operational and tactical levels, and the draft strategies they had on Olympic proved very similar as well. Although they failed to agree on the command issue, they agreed to continue development of the two plans (one concerning the naval and amphibious operations, the other the ground campaign) in consultation with each other. King, Marshall and their respective staffs continued to search for a way to word the invasion directive so that both services would be satisfied.

King then wrote to Marshall expressing concern that the length of time it was taking to resolve the issue might delay the operation past the good weather expected in the autumn and suggested that the Joint Chiefs ignore the mention of command and simply order the invasion date for 1 November 1945. Marshall refused to yield on this subject and considered that they were in complete disagreement and suggested that they put the matter before the Joint Chiefs without any further delay. King then decided to accept the new wording, MacArthur having primary responsibility for the campaign, as well as the amphibious assault, which would be through the appropriate naval commander, while Nimitz would have responsibility for the conduct of the naval and amphibious phases and would correlate his plans with MacArthur's. This was approved and the newly amended 'Directive for Operation Olympic' (JCS 1331/3, 25 May 1945) was forwarded to the Pacific commanders, the target being Kyushu and the date 1 November 1945. For a period of time, between late 1943 to mid-1944, Hokkaido was muted as firstly an interim step between Okinawa and Kyushu, and then as an alternative to Kyushu (outlined in CSP 86/2, 'The Defeat of Japan within Twelve Months of Germany', 25 October 1943) but this was rejected by the Joint War Plans Committee. The Joint Chiefs followed up by ordering that Operation Longtom be deferred indefinitely on 27 May 1945. In June, President Truman asked the Joint Chiefs to meet with him to discuss the proposed invasion of Japan, the conference taking place on 18 June 1945. The Joint Chiefs presented a united front with both King and Marshall arguing that invasion was the only alternative and even Leahy, who was still against the operation, failed to raise an objection. Truman ordered the Joint Chiefs to proceed with Olympic, with the only provision that he be given another review just before the operation was to start.

World War Two: U.S. Military Plans for the Invasion of Japan, Thomas Fensch (Editor) This is a very useful collection of official American documents relating to Operation Downfall, the plan for the invasion of Japan. The invasion never needed to be carried out, but the plans had reached a very advanced stage by the time the two Atomic bombs ended the war. [see more]
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How to cite this article:Antill, P. (21 August 2005), Operation Downfall: The Planned Assault on Japan, 27 April 1296, http://www.historyofwar.org/articles/wars_downfall1.html

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