Operation Downfall: The Planned Assault on Japan

Operation Downfall: The Planned Assault on Japan

Operation Downfall: The Planned Assault on Japan - Japanese Campaign Plan and Troop Dispositions, November 1941

Map 1: Japanese Campaign Plan and Troop Dispositions, November 1941 (courtesy of University of Texas)

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The Secret Is Out : Check Out The Planned American Invasion of Japan

Key point: Thankfully an invasion was not necessary, because it would have been bloody.

One of the most controversial decisions in history was President Harry Truman's decision to drop atomic bombs on Hiroshima and Nagasaki in August 1945.

Some argue that Truman was haunted by estimates that Operation Downfall -- the proposed invasion of Japan in 1945 -- would cost a million American casualties. Others say that Japan was starving and exhausted, the casualty estimates were exaggerated, and that Truman had ulterior motives for dropping the Bomb, namely intimidating the Soviet Union with a display of America's technological might.

Like any counterfactual, there can never be any definitive proof of the outcome of a hypothetical invasion of Japan. But we can make a few reasonable assumptions.

First, we can take a good guess what an amphibious assault on Japan in November or December 1945 would have been like. Fresh in American minds would have been Operation Iceberg, the April 1945 assault on the island of Okinawa, 400 miles from the Japanese mainland and politically a part of Japan proper. Rather than suicidal banzai charges in the face of American firepower, the Japanese changed tactics: they retreated to fortified lines and caves in the Okinawan interior, where they fought for three months and almost to the last man. Meanwhile, wave after wave of kamikaze aircraft dove on U.S. and British Commonwealth ships (even the super-battleship Yamato made a suicide sortie). The result was more than 50,000 U.S. casualties, a quarter-million Japanese military and civilian dead, and more than 400 Allied ships sunk or damaged.

Operation Downfall would have made Okinawa look like a picnic. "The often-repeated common wisdom holds that there were only 5,500, or at most 7,000, aircraft available and that all of Japan’s best pilots had been killed in earlier battles, writes historian D.M Giangreco .

"What the U.S. occupation forces found after the war, however, was that the number of aircraft exceeded 12,700, and thanks to the wholesale conversion of training units into kamikaze formations, there were some 18,600 pilots available. Most were admittedly poor flyers, but due to the massive influx of instructors into combat units, more than 4,200 were rated high enough for either twilight or night missions."

Today's U.S. Navy fears attacks by swarms of Iranian or North Korean small boats, but the Japanese would have unleashed a horde of suicide craft. There were squadrons of training aircraft whose wooden frames were almost invisible to radar, a thousand suicide speedboats, and carefully stockpiled gasoline to power them. The Japanese army was filled with poorly trained conscripts, but they would have been fighting on home ground, in rough and fortified terrain, and backed by a ragtag but indoctrinated civilian militia that would have battled American tanks with farm tools.

As it had against a Mongol amphibious invasion in the 13th Century, the weather gods would have favored Japan. A devastating typhoon in October 1945 would have delayed Allied invasion preparations, while bad weather in the winter and spring of 1946 would have hampered operations and logistics.

Of course, the Allies (Britain and Australia would have contributed warships and aircraft) would have enjoyed air and naval supremacy to isolate and pound Japanese troops, supply lines and whatever factories hadn't been destroyed by U.S. B-29 bombers. They would have had numerous tanks and artillery pieces, and ample ammunition to use all this firepower. But then again, the Allies enjoyed these advantages at the Battle of the Bulge and in Korea, and still suffered heavy losses.

So would Operation Downfall have cost a million American casualties, plus a horrific number of Japanese military and civilian dead? That toll was not guaranteed, but it appears quite possible.

The problem for Harry Truman and his generals was never going to be outright defeat of an invasion, but rather how long and costly the victory. The U.S. had suffered less during the war than other combatants (the advantage of fighting on someone else's soil). Yet by 1945, America was tired of the casualty lists, the rationing, the relentless wartime factory shifts. With the prospect of another year or two of war, there would have been pressure to use the handful of new atomic bombs -- out of frustration as much as military necessity -- and even to use poison gas to subdue the Japanese.

Perhaps a greater man than Truman would have balked at unleashing the monstrous genie of atomic warfare. Yet after six years of the most terrible war in history, greatness was in short supply across the globe, replaced by a desire just to get the slaughter and misery over with and bring the boys home.

The decision to drop the A-bomb may or may not have been the best decision. But it almost certainly was an inevitable one.

Michael Peck is a contributing writer for the National Interest. He can be found on Twitter and Facebook. This first appeared in August 2018 and is being republished due to reader's interest.


The Secret Is Out : Check Out The Planned American Invasion of Japan

Key point: Thankfully an invasion was not necessary, because it would have been bloody.

One of the most controversial decisions in history was President Harry Truman's decision to drop atomic bombs on Hiroshima and Nagasaki in August 1945.

Some argue that Truman was haunted by estimates that Operation Downfall -- the proposed invasion of Japan in 1945 -- would cost a million American casualties. Others say that Japan was starving and exhausted, the casualty estimates were exaggerated, and that Truman had ulterior motives for dropping the Bomb, namely intimidating the Soviet Union with a display of America's technological might.

Like any counterfactual, there can never be any definitive proof of the outcome of a hypothetical invasion of Japan. But we can make a few reasonable assumptions.

First, we can take a good guess what an amphibious assault on Japan in November or December 1945 would have been like. Fresh in American minds would have been Operation Iceberg, the April 1945 assault on the island of Okinawa, 400 miles from the Japanese mainland and politically a part of Japan proper. Rather than suicidal banzai charges in the face of American firepower, the Japanese changed tactics: they retreated to fortified lines and caves in the Okinawan interior, where they fought for three months and almost to the last man. Meanwhile, wave after wave of kamikaze aircraft dove on U.S. and British Commonwealth ships (even the super-battleship Yamato made a suicide sortie). The result was more than 50,000 U.S. casualties, a quarter-million Japanese military and civilian dead, and more than 400 Allied ships sunk or damaged.

Operation Downfall would have made Okinawa look like a picnic. "The often-repeated common wisdom holds that there were only 5,500, or at most 7,000, aircraft available and that all of Japan’s best pilots had been killed in earlier battles, writes historian D.M Giangreco "Hell to Pay: Operation Downfall and the Invasion of Japan 1945-47.

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12 Advantages and Disadvantages of Dropping the Atomic Bomb on Japan

There are two significant events that define the second world war: the Holocaust and the atomic bombs that were dropped on Japan. The decision by the United States to use these weapons in August 1945 is credited with the end of World War II. It is also important to note that those who issue that credit are the ones that were part of the Allied forces during the conflict.

The U.S. only dropped two of these bombs on Japan during the war, but it was a detonation that would be devastating by any definition. More than 80,000 people were killed instantly in Hiroshima on August 6, 1945, when the Little Boy uranium-based bomb was dropped over the city.

Then the plutonium-style bomb called Fat Man was dropped over Nagasaki, which instantly killed 70,000 people. It would take just five days after the second bomb for the emperor to proclaim an unconditional surrender.

When all the effects of the radiation from these two bombs is taken into account, the acute effects would kill up to another 250,000 people in

List of the Pros of Dropping the Atomic Bomb on Japan

1. Despite its devastating impact, each atomic bomb ultimately saved lives.
After the conclusion of the European front in March 1945, Allied forces began turning their attention to Japan. This island nation was the lone holdout in the battle for world domination at the time. The military minds of these countries put together a plan that was called Operation Downfall.

One of the most significant issues in planning this invasion was that the landing locations for an invasion where highly predictable. Japanese forces came to the same conclusions as the Allied planners, so they began to reinforce their key structure points. An all-out defense of Kyushu was planned, with casualty predictions on both sides expected to be very high.

Although the final estimates would vary based on the assessment of the individuals involved, one such document created for the Secretary of War’s staff placed the number at up to 800,000 Allied fatalities, with an additional 10 million Japanese fatalities.

Despite the high number of casualties from Hiroshima and Nagasaki, without the need for Operation Downfall, the actual number of deaths became much lower than anticipated.

2. The action of dropping the two atomic bombs issued in an era of global peace.
The conclusion of World War II created a shift in priorities for the world’s governments. The United Nations came about as an organization to fill in the gap left by the first attempt at the League of Nations. Countries went to war as a way to limit authoritarianism instead of allowing it to spread until it could no longer be contained. Although the United States would face significant conflicts in Korea and Vietnam in the decades following the second world war, the 50-year period between 1951-2000 was one of the most peaceful in the history of recorded human history. There were more threats of wars that governments faced than actual conflicts to fight.

3. We often forget about the fire-bombing campaigns that happened first.
When people debate the morality and ethics of the atomic bombs that were dropped in Japan, they often look at the numbers and discuss the sheer magnitude of the civilian casualties involved – and rightly so. Innocent deaths are always one of the most significant disadvantages of any conflict. The horrors of radiation only magnify this issue exponentially.

What gets left out of this debate was the bombing of Tokyo that occurred before the atomic bombs were dropped. In March 1945, over 100,000 civilians were killed, and another 1 million left homeless, when B-29s dropped a firebomb assault on the city. The government of Japan didn’t blink an eye when that happened. Only the shock of the atomic impact, with its ability to instantly wipe any city off the map, was enough to create movement toward peace.

4. There is no guarantee that the casualties would have changed.
The United States military was planning to firebomb Hiroshima and Nagasaki because of their military influence if the decision on the atomic bombs did not receive a go-ahead. After the destruction experienced in Tokyo, there is an excellent chance that the casualty count would have remained the same. The only difference in the outcome would have been a reduction in future casualties due to the cancer development and birth defects related to radiation exposure. Everyone in these cities were doomed from the moment Allied forces began plotting an eventual end to World War II.

5. It stopped the Soviet Union from repeating its demands from Europe.
When the European theater resolved itself after Allied troops took over Berlin, the Soviet Union began to carve out for itself a nice chunk of space that would eventually become known as the Iron Curtain. It would take over four decades for that veil to fall. The Soviets had their sights set on Japan in the closing days of the war in 1945 as well, envisioning another joint occupation scenario.

Despite the casualties caused by dropping the atomic bombs, the action itself stopped any Soviet ambitions cold in their tracks. The devastating results were so impressive that the Russians backed down from any potential demand to be involved in the Pacific theater. If that hadn’t taken place, the implications of the Cold War to come would have been very different for American politics.

List of the Cons of Dropping the Atomic Bomb on Japan

1. Most of the people killed in these two bombs were innocents.
When one nation targets another and kills over 200,000 people who are not engaged in active conflict, then it could be argued that such an act is the deliberate and systematic destruction of a national group. Although the legal definition of genocide was not created until 1948 under Article 2 of the Convention on the Prevention and Punishment of the Crime of Genocide, far fewer people have been killed by an oversight organization and charged with this act. Incinerate civilians as a way to put pressure on their government might save American lives with an atomic bomb, but isn’t all human life equally valuable?

2. American POWs were killed by the atomic bombs in Japan.
There were a dozen American prisoners of war who were killed when the atomic bombs were dropped on Hiroshima and Nagasaki. They were being held in a police station when the bombs went off. These men, along with up to at least 3,000 American citizens who were living in the cities with relatives, were killed during or immediately after detonation. When history books from the Allied perspective tell the story of what happened, these lives are often not spoken about whatsoever. It shows that Americans were willing to kill their own as way to prevent future casualties.

3. The U.S. killed Allied troops during the bombing runs as well.
There were another 8 British and Dutch prisoners of war that were killed during or immediately after the atomic bombs were dropped on Japan. Even though the Quebec Agreement required that nuclear weapons would only be used when there was mutual consent, so Britain was on-board with the two bombing runs. It should be noted that even President Truman told his Secretary of War that they would only be used on military objects, on soldiers and sailors, and not any women or children. That was why Tokyo and Kyoto were spared in the first place. Unfortunately, the results didn’t end up as intended, even if the cities held military significance.

4. There were more atomic bombs planned for Japan too.
There was another atomic bomb planned to be ready for use on August 19 if the Japanese had decided not to surrender. Another three additional bombs were in the process of being ready for September, with another three to follow in October as well. The actual order for these weapons was to drop them on cities in Japan as they were ready to go. It wasn’t until a response to a memorandum placed on August 10 that changed this to the order of the President.

5. Cancer increases are directly linked to these atomic weapons.
Radiation exposure does not immediately create a surge in cancer cases after the dropping of an atomic weapon. They have a minimum latency period of at least five years, while leukemia cases can sometimes appear in as little as two years, but peaking about 6-8 years after the event. Almost all of the cases of leukemia associated with these bombs involved an exposure of at least 1Gy. Up to 46% of the cancer deaths from the region between 1950-2000 could be potentially related to the fallout of the weapons involved in these attacks.

6. There was an increase in birth defects after the bombs were dropped.
It wasn’t just the current generation that experienced a negative impact because of the atomic bombs falling on Hiroshima and Nagasaki. There was an increase in birth defects that occurred in the years after the event as well. Anyone with an exposure of 0.2Gy or higher faced an increased risk of experiencing this risk. The actual number of miscarriages, stillbirths, and other infant health issues was never documented in Japan after the war, so exact figures are not known.

7. Blockades were just as effective as a fighting strategy to cut off supplies.
Some military strategists argue that Operation Downfall was not even necessary because of the impact that naval blockades around the islands were having. Over 60 significant cities in Japan were already destroyed through conventional bombing techniques before the atomic bombs were dropped. The Soviet Army had attacked Japanese troops in Manchuria with great success. With more resources funneled into this strategy, the potential for an unconditional surrender was possible without changing the way we perceive warfare today.


Operation Downfall: The Planned Assault on Japan - History

Posted on 08/06/2010 7:42:11 AM PDT by tlb

OPERATION DOWNFALL, to be complete within one year of the end of the war in Europe, had two major components.

* Olympic . November 1, 1945. Invasion of Southern Kyushu to provide a large base for naval and air forces within range of Tokyo.

* Coronet . March 1, 1946. Invasion of Central Honshu and Tokyo.

Olympic entailed landing three corps on southern Kyushu, the most southern of the four Japanese home islands. The center portion of Kyushu is almost impassible mountains which would be difficult to transit and was to be used to isolate southern Kyushu from counterattack by Japanese troops from northern Kyushu (Nagasaki). The landings were to be by troops already in the Pacific covered by 34 carriers and by land based aircraft from Okinawa. B-29's would interdict reinforcements. Southern Kyushu had a large bay, harbors, and many airfields. The intent was to base naval support craft and to establish 40 air groups, many redeployed from Europe.

From southern Kyushu, fighter air cover could open the Inland Sea to the US Navy and interdict transportation as far as north as Osaka fighter bombers could close shipping from Korea and China medium bombers and could destroy transportation, material, and installations around Tokyo and support the invasion troops large bombers (B-17 and B-24) could range over all of Japan. Meanwhile, B-29's from the Marianas could continue to wipe out industrial centers.

There were two naval groups.

The Strike Force, 3rd Fleet, had 21 carriers and 10 fast battleships to range up and down the length of Japan to suppress Japanese forces with priority to destroy aircraft and transportation.

The Assault Force, 5th Fleet, had 26 carriers, plus 8 detached from Strike force for the invasion period, 13 slow battleships, 20 cruisers, 139 DD, 167 DE, and support ships for a total of 800 warships. Troops and their equipment were to come from the Philippines and Marianas in 1,500 transports. All combat troops were from the Pacific theater none redeployed from Europe.

The plan called for a diversionary display by the floating reserve on Shikoku, the smallest of Japan's four islands, before their landing on Kyushu. Support troops including engineers to build airfields were to land starting on Y-Day + 2 some of these were to come from Europe.

At the time of the start to planning of Olympic, there were 1-1/2 divisions based on southern Kyushu these with various service bases there amounted to about 45,000 men. Planners expected an additional three divisions to be moved into the area by the time of the landings.

The Japanese were able to predict the landing using the same logic as US planners and moved 9 more divisions into the area for 216,000 men by the time of the surrender in august. More men, material and defenses would have been assembled by the November date for the invasion.

Each side of the central bay had an army, each was divided into two functions - a static defense force on the beaches to fight to the death while allowing reinforcements to arrive, and the mobile reserve to push the American back into the sea. The three logical landing beaches were defended from the shore to the nearby mountains with new troops. The reserves located in the mountains were experienced troops from Manchuria with light tanks. Supporting the troops were the remnants of the navy and air force, lightly armed volunteers, and an array of "special" weapons.

The air forces contained 5,600 conventional combat planes and a similar number of older planes and trainers suitable as Kamikazes. The combat planes were withdrawn from Kyushu and the Kamikazes moved in. Japan was so short of aircraft and fuel that B-29's and carrier task forces were not routinely attacked so as to conserve combat aircraft for the final battle. Equal numbers were assigned to Kyushu and Tokyo areas. As the date for the first battle approached, more were moved to Kyushu with the Tokyo forces to be replaced with promised new production.

Kamikaze tactics were initiated in the Philippines and became a doctrine that inflicted terrible damage to US warships off Okinawa. The invasion of Kyushu would see the distance reduced, flying over familiar land instead of over-water navigation, and with targeting changed from warships to troopships the plan was to inflict intolerable damage to the invasion force before it hit the beach.

The following "special weapons" were established on southern Kyushu.

* Kamikazes -- 2,100 army planes and 2,700 navy planes. * Baku - suicide missile carried by a bomber. * Mini-subs, each with 2 torpedoes, 500 were building. * Fleet submarines -- rearm the 57 remaining that had been dedicated to resupply of outposts. * Kaiten - suicide torpedoes with a 20 mile range. * Shinyo - suicide motorboats. The army had 1-man, 17 foot motorboats. The navy had 2-man, 22 foot boats. * The largest surviving warships were destroyers that were prepared for suicidal attack on the invasion convoys. * On the land, human mines in which soldiers had explosives strapped to their bodies and were to crawl under a tank. Other explosives were packed with a suction cup to be attached to the side of a tank. And shaped charges on a long pole were to be detonated on the side of a tank. * Japanese paratroopers were to attack Okinawa to disrupt flight operations during the invasion period.

Rather than invade Japan, the country could have been blockaded with a ring around the Yellow Sea from Shanghai to Korea. This was not assured to cause the surrender of Japan. The direction of the war would have been towards reinforcing China and supplying the Soviet Union for their movement of troops into Manchuria, Korea, and mainland China.

A plan resurrected after the enemy buildup on Kyushu exceeded all expectations, was the occupation of the less well defended northern island of Hokkaido and northern part of Honshu. This would have been of equal distance from Tokyo, but further from American army, naval, and air force centers. Shipping was already a problem with large numbers unreleased from the Atlantic needed to supply Europe and return troops to the US to redeploy air and service forces from Europe to the Pacific, to supply the Pacific buildup and to move several corps to the invasion sites. Every tanker in the US fleet was required to provide the millions of gallons of fuel required by the ships involved in the Kyushu operation. More fuel and shipping would be required to move 1,100 miles further away to the north. That plan was dropped.

There are two sets of potential casualty figures a low number used to gain approval to proceed with the operation and a high number used to plan reserve forces, medical needs and, as it turned out, to claim as lives saved by use of the atom bomb. These figures changed over time, starting low and going higher as the enemy build-up on Kyushu was discovered.

The low casualty figures were based on the landings at Okinawa, Lingayen Gulf, and Normandy. Okinawa and Lingayen Gulf were undefended on the beaches, the fighting took place in the mountains where each Japanese caused one US wounded of which 20% resulted in US deaths. Normandy had the same three-beach landing pattern, but two beaches were relatively easy, only the landing at "bloody" Omaha was vigorously defended.

All three Kyushu beaches were defended in depth. A shoreline defense such as Omaha beach and a mountain cave defense as on Okinawa all to the death. It would have been more realistic to triple the rate of Omaha beach rather than take the average of the three Normandy beaches as the planners did. There was also a difference in scale. Normandy landed 5 divisions plus 3 airborne divisions. Olympic was to land 14 divisions. Coronet was to have 23 divisions.

The defended beach at Tarawa was a shock to Marine landing with unexpected losses. The US invasion tactic was then changed from surprise to heavy bombardment. The Japanese had to change their defensive positions in the later Pacific actions from defense of the beach to the mountains. Kyushu was to have both forms of defense: well prepared installations near the beaches and well prepared caves in the mountains, with mobile tank forces.

The US planners expected that radar would detect Kamikazes coming through the mountains, carrier fighters would be vectored to intercept them, and proximity-fused ship's anti-aircraft fire would take out any that got through. However, 250 highly maneuverable warships were hit a few months earlier at Okinawa with these same defenses, in open water the prospects of loaded troop ships taking casualties was high and each hit could take half-a-thousand lives. Whereas two Messerschmitts were able to attack troops on the Normandy beaches, 5,000 Kamikaze were aimed at the approaching troop ships while still at sea. It would be reasonable to increase the hit rate of Kamikazes from nearby bases, yet the planners reduced it.

Japanese planners expected almost 500 ships would be sunk during the landing. US planners expected 15-20% losses, they had no experience with mass air attacks on merchant ships at sea.

Good weather was required for close air support on the cloudy islands of Japan. A typhoon had once saved Kyushu from invasion by Mongols in 1281. A storm that forced the carriers to withdraw or even to cause the 2,000 planes to remain on deck, would take away an important part of the invasion support. A storm would also hamper getting supplies over the beaches to the armies.

The original plan was for 9 divisions to attack 3 divisions of defenders. As enemy reinforcements were observed, the size of the invasion force was increased. The final plan had 18 U.S. divisions attacking 11 IJA divisions in defensive positions. Most sources give the advantage to defenders by 3:1, that is, attackers must outnumber defenders by three to be sure of victory.

Casualty figures were a guess that changed with time. There are sufficient numbers available to support any post-war position that any author chooses to take. Low numbers are quoted as reasons to do the invasion, 125,000 for Olympic and to end the war. High numbers, one million US casualties for Downfall, are quoted to justify the A-bomb and end the war. Typically, 25% of casualties are deaths. On average, 5 Japanese soldiers died for each American death.

Japanese casualties were not subjected to planning. If all troops resisted to the death, then the typical survival rate would have only included injured and unconscious soldiers. 216,627 troops were surrendered on Kyushu alone -- more than were expected -- and this was two months before the planned invasion so the number of defenders would have increased. Civilian casualties are a real unknown. 97,000 were killed in the bombing of Tokyo on March 9 the numbers from land warfare would also be high. Consider ratios of any proportion you desire. Civilian losses in some European cities were considerable certainly Japanese casualties would be in the multiple millions.

Coronet was the attack across the Kanto plain to capture Tokyo. The broad plan was still going through refinement.

Naval bombardment by guns and air would begin at Y-15. There would be two simultaneous assaults on Y day.

First Army was to land on the southern half of Kujukuri Beach with 4 divisions to secure a beachhead. On Y+5, with two more divisions landed, they would move across the peninsula to clear the east side of Tokyo Bay and move north to take the port city of Choshi. Service troops would built land-based air bases under the cover of carrier aircraft. Thirty air groups were expected to be in place by Y+30.

Almost simultaneously, Eighth Army would land at Sagami Bay with four divisions to establish a beachhead, secure the Miura Peninsula and Yokosuka naval base. At Y+10, two armored divisions would land and move straight north, beind the industrial cities on Toyko Bay, to establish a blocking position north of Tokyo. Other elements were tasked to take the port cities of Yokohama and Kawasaki to provide supply points for the troops.

First Army was to attack across the Kanto plain to Tokyo about Y+30 with Eighth Army tanks ready to provide assistance. Tokyo had already been extensively destroyed by bombing.

Coronet was a larger operation than Olympic, but the landing on Kyushu, the southern island, was expected to be the more expensive because all of the homeland defensives would have been expended there and the promised replacements to ward off Coronet would have been made industrially impossible. Several thousand Air Force fighters and medium bombers would be flying from a hundred airfields on Kyushu. A 100 carriers could have been available including new construction and those coming from the Atlantic.

The Joint Chiefs expected the Japanese to surrender after exhausting themselves in Operation Olympic. Thus Coronet would not be required.

However, if necessary, follow up operations after Tokyo would have been initiated in the south, central, and north of Japan with US troops from Europe who had taken leave in the US -- only Air Force, air field construction, and service units had gone from Europe directly to the Pacific. And troops from Allied countries would be available.

* South. The northern, more industrialized half of Kyushu would have been taken. * Central. The next largest industrial cities would have been taken with landings to take the peninsulas of Ise Bay, take Nagoya and then march overland to Osaka, Kyoto and Kobe. * North. A landing at Sapporo on Hokkaido followed by taking the anchorage at Mautsu.

Hindsight . Capture of the Marianas as B-29 bases turned out to be the key to the end-game. The campaign in the Philippines and Peleliu were not necessary except to force the final battle with the Japanese fleet and as a place to absorb Japanese army troops and air forces for destruction. Also, an alternative considered at the time, the invasion of Formosa to open access to China and as an alternate base for B-29's would have been equally unnecessary. These resources could have been applied sooner to capture and build air bases at Saipan, Iwo Jima and Okinawa, which were instrumental in the rapid end of the war. But the secret weapon was a secret and it might not have worked or been ready in time.

Olympic - Southern Kyushu Troops . All were US from Pacific area Autumn of 1945 6th Army.

Sep 1 . Honshu, Kyushu, Strategic Air Force (B-29 Okinawa) continue strategic targets. Sep 1 . Shimonoseki Straight / ports, Strategic Air Force continue isolation mining. Sep 18. Hong Kong , British strikes. Sep 28. Canton , British strikes. Oct 1 . Ningpo , Chusan, China , Strategic Air Force isolation bombing. Oct 18. Honshu, Inland Sea , 3rd Fleet : TF-38 (US) , TF-37 (UK) strategic support Oct 21. Kyushu , Strategic Air Force N-S isolation and anti-buildup Oct 24. Kyushu , 5th Fleet preliminary bombardment, mine clearing, interdict highways. Oct 27. Outer Islands , 40th Inf Div Oct 28. Tanega Shima , 158th Reg Combat Team Oct 30. Shikoku , feint by 9th Corp : 77th , 81st , 98th Infantry Divisions Nov 1 . West , 5th Amphibious Corp : 2nd , 3rd , 5th Marine Divisions Nov 1 . South , 11th Corp : 1st Cav , 43rd Inf , Americal Divisions. Nov 1 . East , 1st Corp : 25th , 33rd , 41st Infantry divisions Nov 22. Where needed : 11th Airborn Division. Nov 23. As needed or SW : 9th Corp : 77th , 81st , 98th Infantry Divisions Dec - . Build air fields : support troops and air crews from European theator. Jan - . Attack all military and industrial areas of Japan by air and sea.

Planning Alternatives for Coronet -- Spring of 1946 Coronet was the attack across the Kanto plain to capture Tokyo. The broad plan was still going through refinement and only outline drafts had been completed by August 1.. The initial plan called for three landings using 25 divisions:

* a blocking force landing at Mito on the coast north of Toyko and move west to establish a position north of Tokyo. * the main force landing in Kashima Beach south of Choshi with a goal to clear Chiba province including the east side of Tokyo Bay and build airfields and land tank divisions before moving across the Kanto plain to attack Tokyo from the east. * a southern landing at Sagami Bay 30 days later would take Yokosuka naval base and move rapidly north to be west of Tokyo. * the three armies would then move on Tokyo.

A second plan, subject to further change, dispensed with the northern force and was reduced by 2 divisions. This acknowledged that redeployment from Europe was not going well -- two million experienced veterens were being released and units were in disarray.

* a landing was to be made on Kashima Beach east of Tokyo with 5 divisions to clear Chiba province, cross the Boso peninsula to Tokyo Bay, built land-based air bases under the cover of carrier aircraft, and built up 9 infantry and 2 tank divisions including some redeployed from the European theater. * The major landing was to be made ten days later at Sagami Bay, the outer part of Tokyo Bay, southwest of Tokyo with the goal to take the naval base at Yokosuka and open Toyko Bay and build up to 8 infantry and 3 tank divisions. * Then both armies were to move on Tokyo at D+30.

o The southern, Sagami force, was to move quickly north behind the cities on Tokyo Bay with elements tasked for the ports of Yokohama and Kawasaki, while the main force continued north to be northwest of Tokyo. o Meanwhile the Navy would move into Tokyo Bay to provide support from the south. o One corp is unaccounted for in the surviving drafts of the plan at the time of the surrender, which shows that the planning was still in progress.

A third plan retained the three landings of 25 divisions with 1 paratroop division in reserve. This was MacArthur's plan and assumed that more troops were available than the Joint Chiefs thought possible.


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.


Downfall

In April 1945, Gen. Douglas MacArthur was named Commander in Chief of U.S. Army Forces in the Pacific and designated to lead the invasion of Japan, code- named Operation Downfall. The Operation Olympic phase was to begin Nov. 1 with the objective of seizing the lower third of Kyushu, southernmost of the Japanese home islands. The heart of it would be an amphibious assault operation by nine divisions, compared with six divisions employed in the D-Day landing in Normandy the year before.

The initial expectation was that the nine U.S. divisions would be opposed by three Japanese divisions. That three-to-one ratio satisfied the standard military principle that an offensive force should be significantly larger than the defense force it intends to attack. Even with the updated Ultra estimates in August, the plan for Olympic was not fully adjusted for the 14 Japanese combat divisions in place on Kyushu.

The invasion of Japan was planned in two phases. It would begin with Operation Olympic on Nov. 1, 1945, an amphibious operation a third larger than the D-Day landing in Europe. Mike Tsukamoto/staff

Operation Downfall: America's Plan to Invade Imperial Japan

One of the most controversial decisions in history was President Harry Truman&aposs decision to drop atomic bombs on Hiroshima and Nagasaki in August 1945.

Some argue that Truman was haunted by estimates that Operation Downfall -- the proposed invasion of Japan in 1945 -- would cost a million American casualties. Others say that Japan was starving and exhausted, the casualty estimates were exaggerated, and that Truman had ulterior motives for dropping the Bomb, namely intimidating the Soviet Union with a display of America&aposs technological might.

Like any਌ounterfactual, there can never be any definitive proof of the outcome of a hypothetical invasion of Japan. But we can make a few reasonable assumptions.

First, we can take a good guess what an amphibious assault on Japan in November or December 1945 would have been like. Fresh in American minds would have been Operation Iceberg, the April 1945 assault on the island of Okinawa, 400 miles from the Japanese mainland and politically a part of Japan proper. Rather than suicidal banzai charges in the face of American firepower, the Japanese changed tactics: they retreated to fortified lines and caves in the Okinawan interior, where they fought  for three months and almost to the last man. Meanwhile, wave after wave of kamikaze aircraft dove on U.S. and British Commonwealth ships (even the super-battleship Yamato made a suicide sortie). The result was more than 50,000 U.S. casualties, a quarter-million Japanese military and civilian dead, and more than 400 Allied ships sunk or damaged.

Operation Downfall would have made Okinawa look like a picnic. "The often-repeated common wisdom holds that there were only 5,500, or at most 7,000, aircraft available and that all of Japan’s best pilots had been killed in earlier battles, writes historian D.M Giangreco "Hell to Pay: Operation Downfall and the Invasion of Japan 1945-47.

"What the U.S. occupation forces found after the war, however, was that the number of aircraft exceeded 12,700, and thanks to the wholesale conversion of training units into kamikaze formations, there were some 18,600 pilots available. Most were admittedly poor flyers, but due to the massive influx of instructors into combat units, more than 4,200 were rated high enough for either twilight or night missions."

Today&aposs U.S. Navy fears attacks by swarms of Iranian or North Korean small boats, but the Japanese would have unleashed a horde of suicide craft. There were squadrons of training aircraft whose wooden frames were almost invisible to radar, a thousand suicide speedboats, and carefully stockpiled gasoline to power them. The Japanese army was filled with poorly trained conscripts, but they would have been fighting on home ground, in rough and fortified terrain, and backed by a ragtag but indoctrinated civilian militia that would have battled American tanks with farm tools.

As it had against a Mongol amphibious invasion in the 13th Century, the weather gods would have favored Japan. A devastating typhoon in October 1945 would have delayed Allied invasion preparations, while bad weather in the winter and spring of 1946 would have hampered operations and logistics.

Of course, the Allies (Britain and Australia would have contributed warships and aircraft) would have enjoyed air and naval supremacy to isolate and pound Japanese troops, supply lines and whatever factories hadn&apost been destroyed by U.S. B-29 bombers. They would have had numerous tanks and artillery pieces, and ample ammunition to use all this firepower. But then again, the Allies enjoyed these advantages at the Battle of the Bulge and in Korea, and still suffered heavy losses.

So would Operation Downfall have cost a million American casualties, plus a horrific number of Japanese military and civilian dead? That toll was not guaranteed, but it appears quite possible.

The problem for Harry Truman and his generals was never going to be outright defeat of an invasion, but rather how long and costly the victory. The U.S. had suffered less during the war than other combatants (the advantage of fighting on someone else&aposs soil). Yet by 1945, America was tired of the casualty lists, the rationing, the relentless wartime factory shifts. With the prospect of another year or two of war, there would have been pressure to use the handful of new atomic bombs -- out of frustration as much as military necessity -- and even to use poison gas to subdue the Japanese.

Perhaps a greater man than Truman would have balked at unleashing the monstrous genie of atomic warfare. Yet after six years of the most terrible war in history, greatness was in short supply across the globe, replaced by a desire just to get the slaughter and misery over with and bring the boys home.

The decision to drop the A-bomb may or may not have been the best decision. But it almost certainly was an inevitable one.

Michael Peck is a contributing writer for the National Interest. He can be found onTwitterandFacebook. This first appeared in August 2018.


Japanese Plans and Estimates

By early 1945, Japan's overseas military forces were precariously close to disaster. Confronted by decisive defeats on every battlefield and by a rapidly decreasing war potential on the home front, the Japanese Government and Imperial General Headquarters took serious steps to bolster their last remaining defense lines. Plans for the final struggle in the Homeland provided for the utilization of all available resources, both of men and material, within a wide resistance sphere encompassing the key areas in Japan, Manchuria, and China.

In January 1945, Imperial General Headquarters estimated that the basic strategy of the Allies included the following broad concepts: (1) isolation of Japan from the continental and southern resources areas (2) destruction of her vital industries (3) elimination of Japan's air, naval, and land forces as threats to an amphibious invasion and (4) extension of the effective range of U. S. fighter planes to the heart of the Japanese Homeland.

To carry out these objectives and to prepare for a full-scale invasion it would be necessary, according to the Japanese reasoning, for the United States to strengthen its existing bases and acquire others still closer to Japan. For this reason, Iwo Jima and the Ryukyu Islands were regarded as almost certain targets for future assault.

At the beginning of 1945, Japan was far from ready to meet a full-fledged Allied invasion. Plans to defend the Home Islands were not considered until after the fall of Saipan in July 1944 and even then the outlined preparations were restricted to naval and air force actions with little provision made for ground combat. Even these halfway measures were soon vitiated by the tremendous plane and ship losses incurred in the Philippines Campaign. In the four main islands of Japan Proper only eleven first-line divisions (including 1 armored division) and three brigades were available for ground defense until new or reserve units could be mobilized on a large scale. Strategic coastal areas were partially fortified by the construction of heavy artillery positions but no clear-cut Homeland battle strategy had yet been formed.

By mid January 1945, it had become apparent to the Japanese High Command that a new and comprehensive defense policy was imperative. On 20 January, Imperial General Headquarters issued an outline of policy for future military preparations.

After first stating that the final decisive battle would be waged in Japan Proper, the outline called for an immediate fortification in depth of Japan's defense perimeter. Included in this perimeter were Iwo Jima, Formosa, Okinawa, the Shanghai region, and the south coast of Korea. Resistance in the Philippines was to be maintained as long as possible to delay the advance of the United States forces toward these key positions. While this outer perimeter was being assaulted, the forces in the Homeland would bend every effort to complete preparations for the decisive battle by early Fall of 1945.

On the basis of this general policy directive, Imperial General Headquarters hastened to construct the Homeland defenses. By the end of July 1945, the ground forces in Japan had been increased to a basic strength of thirty line-combat divisions, twenty-four coastal-combat divisions, and twenty-three independent mixed brigades, two armored divisions, seven tank brigades, and three infantry brigades.

Defense preparations in Kyushu and in the Tokyo-Yokohama and Nagoya districts of Honshu were particularly emphasized. The various area armies were called upon to protect all points strategically important for tactical defense, for production, and for communications and to complete their preparations to crush any American invasion.

By April 1945, the course of events made it increasingly probable that Japan would be invaded in late summer or autumn. All key points in the Philippines had fallen Iwo Jima was lost American forces had gained a firm foothold on Okinawa Russia had started to strengthen her forces in Siberia and Germany was on the verge of final defeat. Victory in Europe would provide an additional reservoir of troops and supplies for Allied operations in the Pacific. These climactic developments spurred Imperial General Headquarters to put its paper policies into concrete form and accelerate its preparations for combating a full-scale amphibious invasion. On 8 April, a plan for the final campaign on the Japanese main islands was completed and issued. This plan, designated "Ketsu Operation," embodied an extensive program to utilize Japan's remaining potential in the forthcoming last-ditch battle for the Homeland.

Stressing the necessity for gearing every aspect of national life to the war effort, the "Ketsu Operation" plan provided for the concentration and rapid reinforcement of forces in the critical battle areas of Kyushu and of the Kanto Plain embracing the Tokyo-Yokohama region. Should Kyushu be the initial invasion point, four divisions would be diverted immediately from the Nagoya (Tokai) district, the Kobe-Osaka sector, western Honshu, and Shikoku to reinforce the strength already deployed on the Kyushu battlefronts. Replacements for these divisions would be provided in the centrally located Kobe-Osaka area by the diversion of three or four additional divisions from the Kanto Plain and northern Honshu. On the other hand, should the Tokyo-Yokohama area of the Kanto Plain be invaded first, eight reinforcing divisions would be moved to Nagano and Matsumoto Prefectures north of Nagoya-three from the northern Honshu district, three from the Kobe-Osaka sector, and two from the Kyushu district. If the situation permitted, two divisions from the Nagoya district would also be placed in the Tokyo-Yokohama area. Two divisions advancing from Hokkaido to northern Honshu and five divisions coming from Kyushu and Shikoku to the Kobe-Osaka area would be available for reinforcement.

Considerable difficulty, however, was anticipated in carrying out this plan. Assuming that the United States would destroy land and water communications, the Japanese made provision for these troop movements to be made on foot, with railroads and ships to be used wherever possible. It was estimated that, if Honshu should be assaulted first, sixty-five days would be required to shift the necessary divisions from Kyushu to the Nagoya district, with ten additional days required to arrive at the battlefield.

In April 1945, the accelerated preparations for the defense of the Homeland brought about a reorganization of the Japanese army command. The problems raised by the increasing numbers of troops in Japan, the slow-up of defense preparations caused by the lack of manpower and materials, aggravated transportation difficulties, together with the need for co-ordination of operational and administrative functions, made it necessary to simplify the command system.

Accordingly, Imperial General Headquarters divided Japan into two general army districts-the eastern and western-with a general army headquarters in each. Eastern Japan was put under the First General Army of Marshal Gen Sugiyama, while western Japan came under the Second General Army of Marshal Shunroku Hata. A new General Air Army Command was established for unified control of army air operations in Japan and Korea with headquarters for the First General Army and for the General Air Army in Tokyo, while Second General Army Headquarters was set up in Hiroshima.

Under the command of the First General Army were the Eleventh (northern Honshu), Twelfth (Tokyo-Yokohama), and Thirteenth (Tokai) Area Armies. The Second General Army commanded the Fifteenth (Kobe-Osaka, western Honshu, Shikoku) Area and Sixteenth (Kyushu) Area Armies. The General Air Army controlled the First Air Army (eastern Japan), the 51st, 52nd, and 53rd Air Divisions, and the 30th Fighter Group. The Sixth Air Army (western Japan) remained under the Combined Fleet.

Almost immediately after the stepped-up home defense program was instituted, American air raids became increasingly severe. Transportation and production facilities were greatly damaged and defense preparations were seriously handicapped. It was almost impossible for the Japanese to put up any effective defense against these air attacks. The loss of the Marianas and the Ogasawara chain, left Japan without bases from which to carry out patrolling activities and, consequently, the Japanese air forces had little or no warning of impending raids. In addition, the small number of planes being produced had to be carefully husbanded for the forthcoming great battle in the Homeland and could not be committed to immediate air defense.

Simultaneously with the growing intensity of these air raids, Japan suffered a long series of reverses between April and June 1945. The loss of the Philippines, Germany's capitulation, the fall of Rangoon, and the American capture of Okinawa, all came as major disasters to Japan. United States activities in the Pacific, meanwhile, gave clear indication that a new offensive would be forthcoming against Japan Proper in the near future.

Although the Japanese hastened their preparations against the threat of impending invasion, they were faced with a multitude of serious difficulties. Transportation and communications facilities were disrupted, the people were gradually learning of their country's grave plight, and the entire economic situation was deteriorating rapidly. In May 1945, Homeland defense measures, particularly air and naval, were far behind schedule, while the over-all civilian defense program was still in a disorganized state.

Despite these obstacles, certain air and naval measures had been accomplished. By the summer of 1945, approximately 8,000 suicide or special-attack planes had been produced by converting army and navy fighters, bombers, trainers, and reconnaissance planes. Plans included 2,500 more to be made available by the end of September. Training of pilots was stressed, primarily to develop quickly the ability necessary to fly these craft on suicide missions. Naval preparations also included intensified production of special-attack boats and midget submarines.

With the final loss of Okinawa in late June and the large-scale air raids over their main cities, it became increasingly evident that Japan was in desperate straits-and that the time was fast approaching when the war would be waged in their own islands.

Before any extensive defense measures could be put into effect, the Japanese High Command had to formulate a concrete estimate of Allied intentions. Only by an accurate assessment of the timing and strategy projected in United States plans and by a correct disposition of their own strength, could Japan's military leaders hope to upset or repel an invasion of the mainland.

Opinions within Imperial General Headquarters differed on the question of impending Allied operations. The various views fell into two main categories: one maintaining that the United States would initiate a long-range program of intensified blockade and strategic air bombardment to destroy completely Japan's combat potential, while the other considered that the war would be brought to a decisive stage by an immediate amphibious invasion of Japan Proper. Although these two possibilities were injected into all discussion on strategy, they were not given equal prominence. The majority of Japan's military planners adhered consistently to the latter view-that an Allied invasion in force would be launched as soon as the necessary men and ships could be massed.

In order to carry out definite defense measures, a decision as to which course of action to prepare for became necessary. By 1 July 1945, Imperial General Headquarters adopted the official position that the United States would seek a quick end to the war by an all-out ground force invasion coupled with intensified sea and air operations. It was assumed that new forward bases for air and naval action would be seized in the northern Ryukyus, the Izu Islands, and possibly Quelpart Island. After these preliminary moves, the Japanese expected strong amphibious assaults against the southern part of Japan Proper. Tanega Island, Osumi Peninsula, and other strategic areas in south Kyushu and along the southern coast of Shikoku were named as the most likely targets to be occupied by Allied forces. The possibility of a diversionary feint at Hokkaido to cover the main landings was also taken into account.

In general, the time of the southern Japan operations was placed in the fall of 1945 and the date of the decisive Kanto Plain operation, in the Spring of 1946. The date of invasion, the Japanese thought, would depend to a large degree upon the number of troops and the amount of shipping the United States considered necessary for large-scale successful landings. It was calculated that by the fall of 1945, the United States would be able to mount a total of thirty divisions for amphibious operations against the Homeland and that a cumulative total of fifty divisions could be massed by the spring of 1946.

The general conclusion drawn in the Japanese estimate of Allied capabilities in July 1945 was that the United States was mustering enormous and overwhelming military strength for use against Japan and that the great battle would be joined between early fall of 1945 and spring of 1946.

Geography and Road Net of Kyushu

Kyushu, the southernmost of Japan's four main islands, extends about 200 miles from north to south and has a general width of about 80 to 120 miles from east to west. More than three-quarters of its territory consists of mountainous terrain, with a few plainlands scattered along the coasts.

The road net running across the island was limited and in poor condition. The Kokudo or national highway was a euphemism for a single-loop, two-lane gravel road, badly torn by the heavy military traffic in constant flow over its surface. The highway was built along the island's coast, running on the west down to Kushikino, cutting across to Kagoshima, along the north bay to Miyakonojo, thence north and east to Miyazaki and finally up the east coast. The inland roads were, for the most part, one and a half lanes wide interspersed with frequent "passing" locations and suitable for light transport only. The remaining roads were narrow, primitive, one-way dirt tracks virtually impassable in wet weather.

The main railroad line paralleled generally the route of the highway and consisted of a single-track system with numerous bridges and tunnels that could be easily and quickly blocked when necessary. In the cultivated lowlands, the roads were built on fills rising four to five feet above the surrounding ground. By-passing and detouring would prove extremely difficult. In the mountains, both the roads and railroads were channeled through many cuts, any of which could be sealed against hostile passage. The entire transportation network was subject to complete disruption to prevent movement by attacker and defender alike.


World War II Database


ww2dbase The eventual successful development of the atomic weapons would play a role in the Japanese decision to surrender, but few had the knowledge of the existence of such a research program. Those who knew of its existence could only regard it as a wildcard of sorts, since success was far from being guaranteed. Therefore, the military campaign against Japan proceeded to prepare for an invasion of the Japanese home islands. By this time, Allied naval and air fleets were operating nearly unopposed, attacking targets of their choosing without facing significant opposition.

ww2dbase Naval Bombardments

ww2dbase On 14 Jul 1945, battleships South Dakota, Indiana, and Massachusetts bombarded Kamaishi, Honshu the primary target was the Kamaishi Works of the Japan Iron Company. A small Japanese gunboat attempted to defend against the overwhelming American force. The escorting destroyers moved forth to fire at the small craft due to either the small size of the target or inaccurate American aiming, several destroyer shells flew over the target and exploded in the town, killing civilians and causing fires. As the battleships opened fire on the iron work facilities, smoke from the burning civilian buildings periodically provided a smoke screen for the Japanese. Nevertheless, when the bombardment was completed, Japanese officials estimated that the damage done to the plants required about 65% of the total value of the physical assets to repair, and the repair would take 8 to 12 months to complete. Explosions at the iron works facilities killed many civilians, while nearby refrigeration and fishing industries were also damaged.

ww2dbase On 15 Jul, three Iowa-class battleships Iowa, Missouri, and Wisconsin bombarded industrial targets at Muroran, Hokkaido. The targets were the Wanishi Iron Works plants and the Muroran Works, both of the Japan Steel Company. Despite limited visibility, the successful bombardment caused damages amounting to the loss of about two and a half months of output of coke and a slightly smaller loss of pig iron for the Wanishi Iron Works, and 40% of a month's output for the Muroran Works. The bombardment also significantly disrupted railway, electric, and telephone systems.

ww2dbase On 17 Jul, battleships shelled Hitachi with a stunning count of 1,207 16-inch shells and 292 6-inch shells from light cruisers.

ww2dbase 18 Jul, the North Carolina, Alabama, Iowa, Missouri, and Wisconsin of the US Navy and King George V of the British Navy bombarded Hitachi and surrounding areas, Honshu. Gunfire moderately damaged the Taga Works and Mito Works of Hitachi Manufacturing Company. The Yamate Plant and the copper refining plants of Hitachi Mine also received damages. Civilian targets were also bombarded, causing significant damage to housing sections as well as telephone, power, and water services. Fires spread quickly due to the lack of firefighters (already fled the city).

ww2dbase On 29 and 30 Jul, South Dakota, Indiana, Massachusetts bombarded Hamamatsu, Honshu, during the night. During this bombardment, high explosive and incendiary shells were used, causing widespread damage.

ww2dbase On 9 Aug, a day after the second atomic bomb was dropped on Nagasaki, South Dakota, Indiana, and Massachusetts conducted a second bombardment on Kamaishi, Honshu, destroying what was left from the first bombardment three weeks prior. Tally of shells fired would result to 850 16-inch shells from battleships, 1,440 8-inch shells from heavy cruisers, and a staggering 2,500 5-inch shells from supporting destroyers. If Akabane's observations in Jul were wrong, any remaining faith in Japan's ability to defend itself was crushed by Aug 1945.

ww2dbase Overall, during this period Allied ships fired 4,500 shells from battleships' primary weapons alone.

ww2dbase Aerial Attacks

ww2dbase As early as late 1944, American bombers began a bombing campaign against Japanese cities that killed as many as 500,000 by the end of the Pacific War. For more information on these bombings, please see the WW2DB article Bombing of Tokyo and Other Cities.

ww2dbase On 24 and 28 Jul, 1945, Task Force 38 under Admiral Halsey launched two carrier aircraft attacks against what was left of the Japanese fleet, which by now were confined to their home ports due to the combination of the lack of fuel as well as the near-total Allied air superiority. Most of the vessels were destroyed without being able to get underway, and marked the final destruction of the once proud fleet.

ww2dbase Effect on Japanese Morale

ww2dbase Between the naval blockades and aerial bombings, however willing to fight for their home islands, the Japanese morale was being shaken. Yutaka Akabane, a senior level civil servant, observed:

"It was the raids on the medium and smaller cities which had the worst effect and really brought home to the people the experience of bombing and a demoralization of faith in the outcome of the war. It was bad enough in so large a city as Tokyo, but much worse in the smaller cities, where most of the city would be wiped out. Through May and June the spirit of the people was crushed. (When B-29s dropped propaganda pamphlets) the morale of the people sank terrifically, reaching a low point in July, at which time there was no longer hope of victory or draw but merely desire for ending the war."

ww2dbase The Invasion Plans

ww2dbase As the naval and air forces bombarded Japan, the Allied leaders planned the actual invasion, which was code named Operation Downfall. The responsibility of planning went to Douglas MacArthur, Chester Nimitz, George Marshall, Ernest King, Hap Arnold, and William Leahy. The inter-service rivalry between the US Army and US Navy was addressed by an agreement that, should situation deem necessary, US Army General Douglas MacArthur would assume total command. Regarding the Japanese capacity to defend the Japanese home islands, American planning assumed:

  • "That operations in this area will be opposed not only by the available organized military forces of the Empire, but also by a fanatically hostile population."
  • "That approximately three (3) hostile divisions will be disposed in Southern KYUSHU and an additional three (3) in Northern KYUSHU at initiation of the OLYMPIC operation."
  • "That total hostile forces committed against KYUSHU operations will not exceed eight (8) to ten (10) divisions and that this level will be speedily attained."
  • "That approximately twenty-one (21) hostile divisions, including depot divisions, will be on HONSHU at initiation of that operation Coronet and that fourteen (14) of these divisions may be employed in the KANTO PLAIN area."
  • "That the enemy may withdraw his land-based air forces to the Asiatic Mainland for protection from our neutralizing attacks. That under such circumstances he can possibly amass from 2,000 to 2,500 planes in that area by exercise of rigid economy, and that this force can operate against KYUSHU landings by staging through homeland fields."

ww2dbase The invasion plan called for two separate invasions.

ww2dbase Operation Olympic was the sub-plan that targeted the Japanese home island of Kyushu. It was scheduled to take place on 1 Nov 1945, code named X-Day, with Okinawa acting as the primary staging area. The invasion fleet was to include 42 aircraft carriers, 24 battleships, and over 400 destroyers and destroyer escorts. The fleet would escort 14 American divisions, both Army and Marine Corps, that would form the initial assault force. The American forces were to conquer and hold the southern third of Kyushu. A deceptive operation, Operation Pastel, was to be launched against cities on the Chinese coast and Taiwan in support of Operation Olympic.

ww2dbase Operation Coronet was to take place on 1 Mar 1946, code named Y-Day, assuming Operation Olympic had successfully secured airfields so that additional land-based air support would be available. It was to be the largest amphibious operation in history, with 25 divisions participating in the initial invasion, including those in floating reserve the great invasion force was to include those transferred from the recently-concluded European War. The invasion beaches were to be at Kujikuri on the Boso Peninsula and Hiratsuka at Sagami Bay, and the forces would work their way north across the Kanto plain toward Tokyo.

ww2dbase Because Japanese geography did not provide many invasion beaches, the Japanese organized a strong defense, particularly at Kyushu. Over 10,000 aircraft of various types and sizes were prepared as kamikaze aircraft. Underground networks of bunkers and caves stored food, water, and thousands of tons of ammunition. 2,350,000 regular soldiers and 250,000 garrison troops were deployed, 900,000 of which were stationed in Kyushu by Aug 1945. 32,000,000 militia, in other words all males between the age of 15 and 60 and all females between 17 and 45, were given the task to supplement the regular military their weapons include everything from antique bronze cannons to Arisaka rifles, from bamboo spears to Model 99 light machine guns. Perhaps the eeriest fact was that after the war the United States discovered even children were trained to become suicide bombers when necessarily, strapping explosives around their torsos and rolling under the treads of American tanks. "This was the enemy the Pentagon had learned to fear and hate", said Dan van der Vat, "a country of fanatics dedicated to hara-kiri, determined to slay as many invaders as possible as they went down fighting". Although there was a strong dovish movement in Tokyo to end the war by seeking a conditional surrender, Ketsu-Go (Operation "Decision") continued to move forth, aiming to cause as much casualty as possible in order to sway American popular opinion. If they could cause more casualties than what the American people could accept, they thought, Japan might have a chance at negotiating for an armistice.

ww2dbase Naturally, the American plan considered Japanese resistance. It noted the possibility that the invasion "will be opposed not only by the available organized military forces of the Empire, but also by a fanatically hostile population", which would result in high casualties. In a study done by the United States Joint Chiefs of Staff in Apr 1945, at least 456,000 casualties were to be expected for Operation Olympic alone. Some other evaluations were also done, and their casualty estimates ranged anywhere from 30,000 to 1,000,000. In preparation, the United States manufactured 500,000 Purple Heart medals to award to those injured in combat.

ww2dbase Operation Downfall was never carried out. With the use of the atomic bombs and Russia's sudden declaration of war on Japan, WW2 in Asia ended without the need for the potentially costly invasion. At the date of this writing, over 100,000 of the Purple Heart medals still sat in American government warehouses.

ww2dbase Sources: American Caesar, Nihon Kaigun, Operational Experiences of Fast Battleships, the Pacific Campaign, Wikipedia.

Last Major Update: Mar 2008

Preparations for Invasion of Japan Interactive Map

Preparations for Invasion of Japan Timeline

15 Apr 1945 American carrier aircraft struck Japanese airfields in southern Kyushu, Japan while 300 US Army B-29 bombers conducted raids on Kawasaki and Tokyo.
25 May 1945 Operation Olympic, the invasion of Japan, was approved by the US Joint Chiefs of Staff, setting the date at 1 Nov 1945.
2 Jun 1945 American carrier aircraft of Task Force 38 attacked airfields in southern Kyushu, Japan. On the same day, 12 Japanese ships were sunk or damaged by naval mines in Japanese waters.
3 Jun 1945 American carrier aircraft of Task Force 38 attacked airfields in southern Kyushu, Japan for the second day in a row. On the same day, 7 Japanese ships were sunk or damaged by naval mines in Japanese waters.
8 Jul 1945 Over 100 American fighters struck eastern Honshu, Japan from their bases on Iwo Jima, Japan.
10 Jul 1945 USS Yorktown (Essex-class) arrived off the coast of Japan and launched air strikes on the Tokyo area.
12 Jul 1945 A number of B-25 bombers based in Okinawa attacked military airfields on Kyushu, Japan.
13 Jul 1945 USS Yorktown (Essex-class) launched strikes on the northernmost Japanese island of Hokkaido.
14 Jul 1945 American battleships USS South Dakota, USS Indiana, and USS Massachusetts and escorting destroyers bombarded Kamaishi, Honshu, Japan the primary target was the Kamaishi Works of the Japan Iron Company, but several destroyers shells overshot the target and hit the town, killing many civilians battleship shells were more accurate, destroying about 65% of the industrial complex, but they also killed many civilians this was the first time the Japanese home islands were subjected to naval bombardment. To the north, the sinking of 6 warships and 37 steamers on the ferry route between Honshu and Hokkaido effectively cut off the latter from the rest of the home islands. At Kure, aircraft of US Navy TF 38 damaged carrier Amagi, carrier Katsuragi, and battleship Haruna. Far to the south, the USAAF XXI Bomber Command canceled a long-range P-51 raid from Iwo Jima to attack Meiji and Kagamigahara near Nagoya due to poor weather.
14 Jul 1945 USS Yorktown (Essex-class) launched strikes on the northernmost Japanese island of Hokkaido.
15 Jul 1945 American battleships USS Iowa, USS Missouri, and USS Wisconsin bombarded industrial targets at Muroran, Hokkaido, Japan the main targets were Wanishi Iron Works plants and the Muroran Works. From the air, American naval aircraft attacked northern Honshu and Hokkaido, destroying railways and coal ferries. 104 US Army P-51 fighters based in Iwo Jima Meiji, Kagamigahara, Kowa, Akenogahara, Nagoya, and Suzuko, Japan. B-24 bombers attacked Tomitaka, Usa, Kikaiga-shima, Amami Islands, Yaku-shima, Osumi Islands, and Tamega Island. After sun down, American B-29 bombers mined Japanese waters at Naoetsu and Niigata and Korean waters at Najin, Busan, and Wonsan, while other B-29 bombers attacked and seriously damaged the Nippon Oil Company facilities at Kudamatsu in southwestern Japan.
15 Jul 1945 USS Yorktown (Essex-class) launched strikes on the northernmost Japanese island of Hokkaido.
17 Jul 1945 UK Task Force 37 and US Task Force 38.2 launched their first strike on the Japanese home islands it was the first British attack on Japan in the Pacific War. British Seafire carrier fighters were launched against Japanese airfields at Kionoke, Naruto, and Miyakawa. American warships bombarded Hitachi, Ibaraki Prefecture, Japan. 1,207 16-inch shells from battleships and 292 6-inch shells from cruisers were fired.
18 Jul 1945 American battleships USS North Carolina, USS Alabama, USS Iowa, USS Missouri, and USS Wisconsin and British battleship HMS King George V bombarded Hitachi, Ibaraki Prefecture, Japan with 2,000 shells the Taga Works and Mito Works of Hitachi Manufacturing Company were moderately damaged, and the Yamate Plant and the copper refining plants of Hitachi Mine were lightly damaged. Civilian housing areas were also attacked, causing many deaths.
18 Jul 1945 USS Yorktown (Essex-class) launched raids on the Tokyo area.
18 Jul 1945 Kasuga capsized in her mooring during a US Navy raid on Yokosuka, Japan.
18 Jul 1945 Escort destroyer Yaezakura, construction not yet completed and had been abandoned since the previous month, was destroyed in a US Navy raid on Yokosuka, Japan.
18 Jul 1945 Submarine chaser Harushima and auxiliary patrol vessels Pa No. 37, Pa No. 110, and Pa. No 122 were sunk by US Navy aircraft in the Yokosuka, Japan area.
18 Jul 1945 American naval land-based aircraft attacked targets off Kawajiri and Tsushima Island, Japan the 1,368-ton merchant steamer Chishima Maru and the cargo steamers Tagami Maru and Shintai Maru were sunk.
19 Jul 1945 US Navy Task Force 38 carrier aircraft damaged carrier Amagi, carrier Katsuragi, and battleship Haruna at Kure Naval Shipyard, Japan.
19 Jul 1945 US warships of Task Group 35.4 conducted a final bombardment of radar stations at Nojima Saki about 90 kilometers south of Tokyo, Japan.
20 Jul 1945 HMS Indefatigable joined UK Task Force 37 and US Task Force 38.2 for an attack on the Japanese home islands. On the same day, an US Army B-29 bomber failed to attack the Imperial Palace in Tokyo with a large "Pumpkin" bomb.
24 Jul 1945 British TF 37 launched 416 sorties, 261 of which were sent against the Japanese home islands and 155 were for defensive patrols escort carrier Kaiyo was damaged by British carrier planes. On the same day, American TF 38 launched 600 aircraft against Kure, Nagoya, Osaka, and Miho, sinking battleship-carrier Hyuga, heavy cruiser Tone, and target ship Settsu, and damaging carrier Ryuho, carrier Amagi, battleship-carrier Ise, battleship Haruna, heavy cruiser Aoba, light cruiser Oyodo, transport Kiyokawa Maru the Aichi aircraft factories at Nagoya were seriously damaged.
24 Jul 1945 Settsu was attacked by 30 US Navy F6F-3 fighters while off Kure, Hiroshima, Japan after 1500 hours, suffering one direct bomb hit and five near misses. Captain Masanao Ofuji grounded her on the island of Etajima to prevent sinking.
24 Jul 1945 USS Yorktown (Essex-class) and TF58 pounded shipping and installations around the Kure naval base.
25 Jul 1945 US carrier aircraft attacked Japanese shipping in the Inland Sea near Osaka and Nagoya, Japan.
25 Jul 1945 USS Yorktown (Essex-class) and TF58 pounded shipping and installations around the Kure naval base.
27 Jul 1945 USS Yorktown (Essex-class) and TF58 pounded shipping and installations around the Kure naval base.
27 Jul 1945 A mine laid by USAAF B-29 aircraft sank the 1,025-ton Japanese army cargo ship Unten Maru in the in the western portion of the Inland Sea of Japan.
27 Jul 1945 A mine laid by USAAF B-29 aircraft sank the 887-ton Japanese merchant cargo ship Meiko Maru off Kogushi, Shimonoseki, Yamaguchi Prefecture, Japan.
27 Jul 1945 A mine laid by USAAF B-29 aircraft sank the Japanese merchant cargo ship Banshu Maru No. 55 in Odo Strait, Shimonoseki, Yamaguchi Prefecture, Japan.
27 Jul 1945 US aircraft damaged the Japanese merchant cargo ship Rokuzan Maru off the southeast coast of Korea.
27 Jul 1945 USAAF B-25 and P-51 aircraft on anti-shipping sweep off the southeast coast of Korea sank the 886-ton Japanese tanker Yushin Maru.
28 Jul 1945 137 American P-47 aircraft based in Ie Shima, Okinawa, Japan attacked targest in Kyushu, Japan. On the same day, 471 B-29 bombers attacked smaller Japanese cities in the home islands with incendiary bombs. Finally, from the sea, US Navy TF 38 struck Inland Sea between Nagoya and northern Kyushu, sinking battleship Haruna, battleship-carrier Ise, heavy cruiser Aoba, and light cruiser Oyodo, and damaging carrier Katsuragi and carrier Hosho.
28 Jul 1945 While beached on the island of Etajima, Hiroshima, Japan, Settsu was attacked by 3 US Navy carrier aircraft, suffering two direct bomb hits.
28 Jul 1945 USS Yorktown (Essex-class) and TF58 pounded shipping and installations around the Kure naval base.
28 Jul 1945 US carrier aircraft attacked Ise at Kure, Japan, scoring 18 hits and many near misses, sinking her in shallow water.
29 Jul 1945 American battleships USS South Dakota, USS Indiana, and USS Massachusetts began a two-day bombardment of Hamamatsu, Shizuoka Prefecture, Japan.
29 Jul 1945 USS Yorktown (Essex-class) launched raids on the Tokyo area.
30 Jul 1945 American battleships USS South Dakota, USS Indiana, and USS Massachusetts ended a two-day bombardment of Hamamatsu, Shizuoka Prefecture, Japan. Meanwhile, carrier fighters attacked airfields, railroads, and tactical targets in the Kobe-Osaka region.
30 Jul 1945 USS Yorktown (Essex-class) launched raids on the Tokyo area.
4 Aug 1945 In a public statement, Douglas MacArthur announced that "a mighty invasion force is being forged", referring to the seemingly impending invasion of the Japanese home islands.
8 Aug 1945 USS Yorktown (Essex-class) launched raids on northern Honshu and southern Hokkaido, Japan.
9 Aug 1945 258 British Avenger, Corsair, Hellcat, Firefly, and Seafire carrier aircraft of Task Force 37 expended more than 120 tons of bombs and cannon shells on targets in and near the Japanese home islands. Meanwhile, American battleships USS South Dakota, USS Indiana, and USS Massachusetts bombarded Kamaishi, Iwate, Japan. 850 16-inch shells from battleships, 1,440 8-inch shells from cruisers, and 2,500 5-inch shells from destroyers were fired.
9 Aug 1945 USS Yorktown (Essex-class) launched raids on northern Honshu and southern Hokkaido, Japan.
10 Aug 1945 USS Yorktown (Essex-class) launched raids on Tokyo, Japan.
13 Aug 1945 USS Yorktown (Essex-class) launched raids on Tokyo, Japan.
1 Nov 1945 This date was the scheduled launch day for Operation Olympic, the invasion of Kyushu, Japan, which never took place.

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Ending the War

With Okinawa secured and American bombers regularly bombing and firebombing Japanese cities, planning moved forward for the invasion of Japan. Codenamed Operation Downfall, the plan called for the invasion of southern Kyushu (Operation Olympic) followed by seizing the Kanto Plain near Tokyo (Operation Coronet). Due to the geography of Japan, the Japanese high command had ascertained Allied intentions and planned their defenses accordingly. As planning moved forward, casualty estimates of 1.7 to 4 million for the invasion were presented to Secretary of War Henry Stimson. With this in mind, President Harry S. Truman authorized the use of the new atom bomb to bring a swift end to the war.

Flying from Tinian, the B-29 Enola Gay dropped the first atom bomb on Hiroshima on August 6, 1945, destroying the city. A second B-29, Bockscar, dropped a second on Nagasaki three days later. On August 8, following the Hiroshima bombing, the Soviet Union renounced its nonaggression pact with Japan and attacked into Manchuria. Facing these new threats, Japan unconditionally surrendered on August 15. On September 2, aboard the battleship USS Missouri in Tokyo Bay, the Japanese delegation formally signed the instrument of surrender ending World War II.