Declassified Plans For the Invasion of Japan

Deep in the recesses of the National Archives in Washington, D.C., hidden for nearly four decades lie thousands of pages of yellowing and dusty documents stamped "Top Secret." These documents, now declassified, are the plans for Operation Downfall, the invasion of Japan during World War II.

Only a few Americans in 1945 were aware of the elaborate plans that had been prepared for the Allied Invasion of the Japanese home islands. Even fewer today are aware of the defenses the Japanese had prepared to counter the invasion had it been launched. Operation Downfall was finalized during the spring and summer of 1945. It called for two massive military undertakings to be carried out in succession and aimed at the heart of the Japanese Empire.

In the first invasion - code-named "Operation Olympic"- American combat troops would land on Japan by amphibious assault during the early morning hours of November 1, 1945 - 69 years ago. Fourteen combat divisions of soldiers and Marines would land on heavily fortified and defended Kyushu, the southernmost of the Japanese home islands, after an unprecedented naval and aerial bombardment.

The second invasion on March 1, 1946 - codenamed "Operation Coronet"- would send at least 22 divisions against 1 million Japanese defenders on the main island of Honshu and the Tokyo Plain. Its goal: the unconditional surrender of Japan.

With the exception of a part of the British Pacific Fleet, Operation Downfall was to be a strictly American operation. It called for using the entire Marine Corps, the entire Pacific Navy, elements of the 7th Army Air Force, the 8th Air Force (recently redeployed from Europe), 10th Air Force and the American Far Eastern Air Force. More than 1.5 million combat soldiers, with 3 million more in support or more than 40% of all servicemen still in uniform in 1945 - would be directly involved in the two amphibious assaults. Casualties were expected to be extremely heavy.

Admiral William Leahy estimated that there would be more than 250,000 Americans killed or wounded on Kyushu alone. General Charles Willoughby, chief of intelligence for General Douglas MacArthur, the Supreme Commander of the Southwest Pacific, estimated American casualties would be one million men by the fall of 1946. Willoughby's own intelligence staff considered this to be a conservative estimate.

During the summer of 1945, America had little time to prepare for such an endeavor, but top military leaders were in almost unanimous agreement that an invasion was necessary.

While naval blockade and strategic bombing of Japan was considered to be useful, General MacArthur, for instance, did not believe a blockade would bring about an unconditional surrender. The advocates for invasion agreed that while a naval blockade chokes, it does not kill; and through strategic bombing might destroy cities, it leaves whole armies intact.

So on May 25, 1945, the Joint Chiefs of Staff, after extensive deliberation, issued to General MacArthur, Admiral Chester Nimitz, and Army Air Force Gene Henry Arnold, the top-secret directive to proceed with the invasion of Kyushu. The target date was after the typhoon season.

President Truman approved the plans for the invasions July 24. Two days later, the United Nations issued the Potsdam Proclamation, which called upon Japan to surrender unconditionally or face total destruction. Three days later, the Japanese governmental news agency broadcast to the world that Japan would ignore the proclamation and would refuse to surrender. During this same period it was learned - via monitoring Japanese radio broadcasts - that Japan had closed all schools and mobilized its school children, was arming its civilian population and was fortifying caves and building underground defenses.

Operation Olympic called for a four-pronged assault on Kyushu. Its purpose was to seize and control the southern one-third of that island and establish naval and air bases, to tighten the naval blockade of the home islands, to destroy units of the main Japanese army and to support the later invasion of the Tokyo Plain.

The preliminary invasion would begin October 27 when the 40th Infantry Division would land on a series of small islands west and southwest of Kyushu. At the same time, the 158th Regimental Combat Team would invade and occupy a small island 28 miles south of Kyushu. On these islands, seaplane bases would be established and radar would be set up to provide advance air warning for the invasion fleet, to serve as fighter direction centers for the carrier-based aircraft and to provide an emergency anchorage for the invasion fleet, should things not go well on the day of the invasion.

As the invasion grew imminent, the massive firepower of the Navy - the Third and Fifth Fleets -- would approach Japan. The Third Fleet, under Admiral William "Bull" Halsey, with its big guns and naval aircraft, would provide strategic support for the operation against Honshu and Hokkaido. Halsey's fleet would be composed of battleships, heavy cruisers, destroyers, dozens of support ships and three fast carrier task groups. From these carriers, hundreds of Navy fighters, dive bombers, and torpedo planes would hit targets all over the island of Honshu The 3,000 ship Fifth Fleet, under Admiral Raymond Spruance, would carry the invasion troops.

Several days before the invasion, the battleships, heavy cruisers, and destroyers would pour thousands of tons of high explosives into the target areas. They would not cease the bombardment until after the land forces had been launched. During the early morning hours of November 1, the invasion would begin. Thousands of soldiers and Marines would pour ashore on beaches all along the eastern, southeastern, southern and western coasts of Kyushu. Waves of Helldivers, Dauntless dive bombers, Avengers, Corsairs, and Hellcats from 66 aircraft carriers would bomb, rocket and strafe enemy defenses, gun emplacements, and troop concentrations along the beaches.

The Eastern Assault Force consisting of the 25th, 33rd, and 41st Infantry Divisions, would land near Miyaski, at beaches called Austin, Buick, Cadillac, Chevrolet, Chrysler, and Ford, and move inland to attempt to capture the city and its nearby airfield. The Southern Assault Force, consisting of the 1st Cavalry Division, the 43rd Division and Americal Division would land inside Ariake Bay at beaches labeled DeSoto, Dusenberg, Essex, Ford, and Franklin and attempt to capture Shibushi and the city of Kanoya and its airfield.

On the western shore of Kyushu, at beaches Pontiac, Reo, Rolls Royce, Saxon, Star, Studebaker, Stutz, Winston and Zephyr, the V Amphibious Corps would land the 2nd, 3rd, and 5th Marine Divisions, sending half of its force inland to Sendai and the other half to the port city of Kagoshima.

On November 4, the Reserve Force, consisting of the 81st and 98th Infantry Divisions and the 11th Airborne Division, after feigning an attack on the island of Shikoku, would be landed - if not needed elsewhere - near Kaimondake, near the southernmost tip of Kagoshima Bay, at the beaches designated Locomobile, Lincoln, LaSalle, Hupmobile, Moon, Mercedes, Maxwell, Overland, Oldsmobile, Packard, and Plymouth.

Olympic was not just a plan for invasion, but for conquest and occupation as well. It was expected to take four months to achieve its objective, with the three fresh American divisions per month to be landed in support of that operation if needed. If all went well with Olympic, Coronet would be launched March 1, 1946. Coronet would be twice the size of Olympic, with as many as 28 divisions landing on Honshu.

All along the coast east of Tokyo, the American 1st Army would land the 5th, 7th 6th Marine Divisions. At Sagami Bay, just south of Tokyo, the entire 8th and 10th Armies would strike north and east to clear the long western shore of Tokyo Bay and attempt to go as far as Yokohama. The assault troops landing south of Tokyo would be the 4th, 6th, 8th, 24th, 31st, 37th, 38th, and 8th Infantry Divisions, along with the 13th and 20th Armored Divisions.

Following the initial assault, eight more divisions - the 2nd, 28th, 35th, 91st, 95th, 97th, and 104th Infantry Divisions and the 11th Airborne Division - would be landed. If additional troops were needed, as expected, other divisions redeployed from Europe and undergoing training in the United States would be shipped to Japan in what was hoped to be the final push.

Captured Japanese documents and post-war interrogations of Japanese military leaders disclose that information concerning the number of Japanese planes available for the defense of the home islands was dangerously in error. 

During the sea battle at Okinawa alone, Japanese Kamikaze aircraft sank 32 Allied ships and damaged more than 400 others. But during the summer of 1945 American top brass concluded that the Japanese had spent their air force since American bombers and fighters daily flew unmolested over Japan.

What the military leaders did not know was that by the end of July the Japanese had been saving all aircraft, fuel, and pilots in reserve, and had been feverishly building new planes for the decisive battle for their homeland.

As part of Ketsu-Go, the name for the plan to defend Japan - the Japanese were building 20 suicide takeoff strips in southern Kyushu with underground hangars. They also had 35 camouflaged airfields and nine seaplane bases.

On the night before the expected invasion, 50 Japanese seaplane bombers, 100 former carrier aircraft, and 50 land based army planes were to be launched in a suicide attack on the fleet.

The Japanese had 58 more airfields in Korea, western Honshu and Shikoku, which also were to be used for massive suicide attacks.

Allied intelligence had established that the Japanese had no more than 2,500 aircraft of which they guessed 300 would be deployed in suicide attacks. In August 1945, however, unknown to Allied intelligence, the Japanese still had 5,651 army and 7,074 navy aircraft, for a total of 12,725 planes of all types. Every village had some type of aircraft manufacturing activity hidden in mines, railway tunnels, under viaducts and in basements of department stores, work was being done to construct new planes.

Additionally, the Japanese were building newer and more effective models of the Okka, a rocket-propelled bomb much like the German V-1, but flown by a suicide pilot. When the invasion became imminent, Ketsu-Go called for a fourfold aerial plan of attack to destroy up to 800 Allied ships.

While Allied ships were approaching Japan, but still in the open seas, an initial force of 2,000 army and navy fighters were to fight to the death to control the skies over Kyushu. A second force of 330 navy combat pilots was to attack the main body of the task force to keep it from using its fire support and air cover to protect the troop carrying transports. While these two forces were engaged, a third force of 825 suicide planes was to hit the American transports. As the invasion convoys approached their anchorages, another 2,000 suicide planes were to be launched in waves of 200 to 300, to be used in hour by hour attacks.

By mid-morning of the first day of the invasion, most of the American land-based aircraft would be forced to return to their bases, leaving the defense against the suicide planes to the carrier pilots and the shipboard gunners. Carrier pilots crippled by fatigue would have to land time and time again to re-arm and refuel. Guns would malfunction from the heat of continuous firing and ammunition would become scarce. Gun crews would be exhausted by nightfall, but still the waves of kamikaze would continue. With the fleet hovering off the beaches, all remaining Japanese aircraft would be committed to nonstop suicide attacks, which the Japanese hoped could be sustained for 10 days. The Japanese planned to coordinate their air strikes with attacks from the 40 remaining submarines from the Imperial Navy - some armed with Long Lance torpedoes with a range of 20 miles - when the invasion fleet was 180 miles off Kyushu.

The Imperial Navy had 23 destroyers and two cruisers which were operational. These ships were to be used to counterattack the American invasion. A number of the destroyers were to be beached at the last minute to be used as anti-invasion gun platforms. Once offshore, the invasion fleet would be forced to defend not only against the attacks from the air but would also be confronted with suicide attacks from the sea. Japan had established a suicide naval attack unit of midget submarines, human torpedoes, and exploding motorboats. The goal of the Japanese was to shatter the invasion before the landing. The Japanese were convinced the Americans would back off or become so demoralized that they would then accept a less-than-unconditional surrender and a more honorable and face-saving end for the Japanese. But as horrible as the battle of Japan would be off the beaches, it would be on Japanese soil that the American forces would face the most rugged and fanatical defense encountered during the war.

Throughout the island-hopping Pacific campaign, Allied troops had always outnumbered the Japanese by 2 to 1 and sometimes 3 to 1. In Japan, it would be different. By virtue of a combination of cunning, guesswork, and brilliant military reasoning, a number of Japan's top military leaders were able to deduce, not only when, but where, the United States would land its first invasion forces.

Facing the 14 American divisions landing at Kyushu would be 14 Japanese divisions, 7 independent mixed brigades, 3 tank brigades and thousands of naval troops. On Kyushu, the odds would be 3 to 2 in favor of the Japanese, with 790,000 enemy defenders against 550,000 Americans. This time the bulk of the Japanese defenders would not be the poorly trained and ill-equipped labor battalions that the Americans had faced in the earlier campaigns.

The Japanese defenders would be the hard core of the home army. These troops were well-fed and well equipped. They were familiar with the terrain, had stockpiles of arms and ammunition, and had developed an effective system of transportation and supply almost invisible from the air. Many of these Japanese troops were the elite of the army, and they were swollen with a fanatical fighting spirit.

Japan's network of beach defenses consisted of offshore mines, thousands of suicide scuba divers attacking landing craft, and mines planted on the beaches. Coming ashore, the American Eastern amphibious assault forces at Miyazaki would face three Japanese divisions, and two others poised for a counterattack. Awaiting the Southeastern attack force at Ariake Bay was an entire division and at least one mixed infantry brigade.

On the western shores of Kyushu, the Marines would face the most brutal opposition. Along the invasion beaches would be the three Japanese divisions, a tank brigade, a mixed infantry brigade and an artillery command Components of two divisions would also be poised to launch counterattacks. If not needed to reinforce the primary landing beaches, the American Reserve Force would be landed at the base of Kagoshima Bay November 4, where they would be confronted by two mixed infantry brigades, parts of two infantry divisions and thousands of naval troops.

All along the invasion beaches, American troops would face coastal batteries, anti-landing obstacles and a network of heavily fortified pillboxes, bunkers, and underground fortresses. As Americans waded ashore, they would face intense artillery and mortar fire as they worked their way through concrete rubble and barbed-wire entanglements arranged to funnel them into the muzzles of these Japanese guns. On the beaches and beyond would be hundreds of Japanese machine gun positions, beach mines, booby traps, trip-wire mines and sniper units. Suicide units concealed in "spider holes" would engage the troops as they passed nearby. In the heat of battle, Japanese infiltration units would be sent to reap havoc in the American lines by cutting phone and communication lines. Some of the Japanese troops would be in American uniform; English-speaking Japanese officers were assigned to break in on American radio traffic to call off artillery fire, to order retreats and to further confuse troops. Other infiltration with demolition charges strapped on their chests or backs would attempt to blow up American tanks, artillery pieces, and ammunition stores as they were unloaded ashore. 

Beyond the beaches were large artillery pieces situated to bring down a curtain of fire on the beach. Some of these large guns were mounted on railroad tracks running in and out of caves protected by concrete and steel. The battle for Japan would be won by what Simon Bolivar Buckner, a lieutenant general in the Confederate army during the Civil War, had called Prairie Dog Warfare." This type of fighting was almost unknown to the ground troops in Europe and the Mediterranean. It was peculiar only to the soldiers and Marines who fought the Japanese on islands all over the Pacific - at Tarawa, Saipan, Iwo Jima and Okinawa. Prairie Dog Warfare was a battle for yards, feet and sometimes inches. It was a brutal, deadly and dangerous form of combat aimed at an underground, heavily fortified, non-retreating enemy. In the mountains behind the Japanese beaches were underground networks of caves, bunkers, command posts and hospitals connected by miles of tunnels with dozens of entrances and exits. Some of these complexes could hold up to 1,000 troops.

In addition to the use of poison gas and bacteriological warfare (which the Japanese had experimented with), Japan mobilized its citizenry. Had Olympic come about, the Japanese civilian population, inflamed by a national slogan - "One Hundred Million Will Die for the Emperor and Nation" - were prepared to fight to the death Twenty Eight Million Japanese had become a part of the National Volunteer Combat Force. They were armed with ancient rifles, lunge mines, satchel charges, Molotov cocktails and one-shot black powder mortars. Others were armed with swords, long bows, axes and bamboo spears. The civilian units were to be used in nighttime attacks, hit and run maneuvers, delaying actions and massive suicide charges at the weaker American positions.

At the early stage of the invasion, 1,000 Japanese and American soldiers would be dying every hour. 

The invasion of Japan never became a reality because, on August 6, 1945, an atomic bomb was exploded over Hiroshima. Three days later, a second bomb was dropped on Nagasaki. Within days the war with Japan was at a close. 

Had these bombs not been dropped and had the invasion been launched as scheduled, combat casualties in Japan would have been at a minimum of the tens of thousands. Every foot of Japanese soil would have been paid for by Japanese and American lives. One can only guess at how many civilians would have committed suicide in their homes or in futile mass military attacks. In retrospect, the 1 million American men who were to be the casualties of the invasion were instead lucky enough to survive the war.

Intelligence studies and military estimates made 50 years ago, and not latter-day speculation, clearly indicate that the battle for Japan might well have resulted in the biggest bloodbath in the history of modern warfare. Far worse would be what might have happened to Japan as a nation and as a culture. When the invasion came, it would have come after several months of fire-bombing all of the remaining Japanese cities. The cost in human life that resulted from the two atomic blasts would be small in comparison to the total number of Japanese lives that would have been lost by this aerial devastation.

Source: Joey L. French, Partner Emeritus Firm Ambassador.