Few historical counterfactuals are as sobering as the prospect of a full-scale U.S. invasion of the Japanese home islands in 1945. By the summer of that year, Japan’s strategic position was untenable. The Imperial Navy had been shattered, American bombers roamed its skies with impunity, and a naval blockade was strangling its economy. Yet, the war’s inevitable outcome should not be mistaken for an inevitable collapse. Had the Allies executed Operation Downfall—the two-stage invasion of Kyushu and Honshu—the result would have been a bloodbath unprecedented even by the standards of the Pacific War.
Operation Downfall: The Planned Invasion
The Allied war plan consisted of two primary phases: Operation Olympic, a November 1945 invasion of Kyushu, followed by Operation Coronet, the assault on Honshu and the Tokyo Plain in early 1946. Together, they represented the largest amphibious operation ever conceived, with an initial landing force of nearly 750,000 men and follow-on reinforcements that would bring total Allied strength to over 3.5 million troops.
The U.S. military expected fanatical resistance. Japanese doctrine emphasized total war, and the government had mobilized civilians—men, women, and even children—to fight with whatever weapons were available. Kamikaze planes had already inflicted serious damage on the U.S. fleet off Okinawa, and Japan still possessed thousands of aircraft, many of which were earmarked for suicide missions.
Japan’s Defensive Preparations
Japanese military planners were fully aware of the futility of their strategic position. However, their goal was not victory but inflicting such staggering casualties that the Americans might reconsider their war aims and seek a negotiated peace. Japan had stationed some 900,000 troops in Kyushu alone, many well entrenched in fortified caves, bunkers, and defensive tunnels.
The Ketsu-Go strategy, or “Decisive Operation,” called for massed kamikaze attacks, with estimates of 10,000 aircraft ready for suicide missions against U.S. landing forces. The Tokko (Special Attack) units were also preparing midget submarines, speedboats loaded with explosives, and human torpedoes. On land, the Japanese had prepared countless defensive positions across Kyushu and Honshu, many modeled on the fanatical resistance encountered in Iwo Jima and Okinawa.
Perhaps most chillingly, the civilian population had been conscripted into a last-ditch resistance force known as the Patriotic Citizens Fighting Corps. Armed with bamboo spears, grenades, and whatever weapons could be mustered, millions of men, women, and even schoolchildren were expected to sacrifice themselves in futile human-wave attacks against battle-hardened U.S. troops. The civilian toll would have been catastrophic.
The Human and Material Cost
U.S. estimates for the invasion’s casualties varied widely. Early projections from Operation Olympic suggested between 250,000 and 500,000 Allied dead, with total casualties (including wounded) exceeding a million. The Japanese toll, both military and civilian, would have been incomprehensibly higher—potentially reaching into the millions.
The lessons of Okinawa, where over 100,000 Japanese soldiers fought to near annihilation and at least 150,000 civilians perished, suggested that the homeland battles would dwarf any previous carnage. American commanders braced for a campaign where every city would become a mini-Stalingrad, fought street by street, bunker by bunker, with civilians caught in the crossfire or dying en masse by their own government’s orders.
The Soviet Factor
Another oft-overlooked variable was the Soviet invasion of Manchuria in August 1945. Had Operation Downfall proceeded, the Soviet Union might have seized northern Hokkaido, leading to a divided Japan reminiscent of post-war Germany and Korea. Soviet involvement could have drastically altered Japan’s post-war fate, potentially leading to a communist foothold in East Asia decades before the Korean and Vietnam Wars.
Would Japan Have Fought to the Last Man?
Despite the harrowing expectations, there remains debate as to whether Japan would have fought to literal extermination. Some elements of the military leadership—particularly the fanatical War Minister Korechika Anami—advocated for total resistance. However, others, including Emperor Hirohito, were increasingly aware of the war’s hopelessness. Had the U.S. landed, internal divisions within Japan’s leadership may have accelerated an eventual surrender, though at a still-unfathomable cost.
Conclusion: A Catastrophe Averted
The atomic bombings of Hiroshima and Nagasaki—and, arguably, the Soviet invasion of Manchuria—forced Japan’s leadership into an abrupt and humiliating surrender. The horror of those bombs remains a source of historical debate, but they likely prevented an even greater catastrophe. Had the U.S. landed on the Japanese mainland, the war would have ground on for months, if not years, in a bloodbath that would have dwarfed all previous engagements in the Pacific.
Thus, Japan’s fate in a ground war was never in doubt. It would have lost. But at what cost? For the Japanese people, the answer might have been national annihilation.
