As World War II came to a close, the United States was preparing for Operation Downfall, a vast, two-phase invasion strategy designed to compel Japan’s surrender. Military officials anticipated the operation would result in enormous casualties, with significant losses on both sides. The plan called for the deployment of hundreds of thousands of Allied soldiers to Japan’s main islands, where they expected fierce opposition from both Japanese military forces and civilians.
Despite the extensive planning and supply buildup, the invasion was ultimately never carried out.
Developing Operation Downfall
After D-Day, it became increasingly evident that the conflict in Europe was approaching its end. However, the road to peace in the Pacific remained distant.
In early 1945, the Combined Chiefs of Staff gathered at the Argonaut Conference to outline a definitive strategy for concluding the war. This meeting laid the groundwork for what would come to be known as Operation Downfall, the planned American-led invasion of Japan.
The operation was based on the assumption that fighting in Europe would end by July 1, 1945, and that the ongoing Okinawa invasion would be completed by mid-August. Operation Downfall was structured into two main phases, set for November 1945 and early 1946.
The first phase would use forces already stationed in the Pacific Theater, while the second phase would involve additional troops redeployed after the end of the European conflict. The scale of this operation was staggering, expected to surpass even the massive D-Day landings.
Operation Olympic
Operation Olympic, the first phase of the larger Downfall strategy, was scheduled to begin on November 1, 1945. The plan called for an assault on the Japanese island of Kyūshū, which would be launched from Okinawa, a heavily fortified base recently secured by U.S. forces. Okinawa was also designated as the primary starting point for troops involved in the subsequent phase, Operation Coronet.
The invasion required an immense naval presence, with 400 destroyers and escort ships, 24 battleships, 42 aircraft carriers, 14 divisions, and two regimental combat teams. A fleet from the Commonwealth, consisting of four battleships and 18 aircraft carriers, would join the effort.
Air support for the naval operations would come from the Fifth, Seventh, and Thirteenth Air Forces, which would also help secure landing zones. Additionally, long-range bombing missions were planned, with the U.S. Strategic Air Forces in the Pacific (USASTAF) and Britain’s Tiger Force taking the lead, alongside support from the RAF’s No. 617 Squadron, famously known as the “Dambusters.”
Operation Coronet
After the expected success of Operation Olympic, the U.S. had a second invasion plan aimed at putting even more pressure on Japan by targeting Honshu. This next phase, called “Y-Day,” was scheduled for March 1, 1946, and was meant to bring the fighting even closer to Tokyo.
The plan involved landing 25 U.S. divisions from the First and Eighth Armies at Kujūkuri Beach and Hiratsuka. These forces would then be supported by 20 more divisions to help push deeper inland.
To strengthen the assault even further, five Commonwealth Corps divisions—made up of British, Canadian, and Australian troops—were added to the operation. Although they weren’t part of the original strategy, they were later included to help American forces surround Tokyo and advance toward Nagano.
Operation Downfall’s success would have come at a heavy price
While the Americans created a concrete plan for invading Japan, Operation Downfall would have come at a heavy price. As part of the preparation, they did calculations to see what the estimated casualties would be. While the numbers varied, the outcome was always staggeringly high.
One approach taken by Fleet Adm. William Leahy was that the casualties would be similar in number to those experienced on Okinawa – 35 percent. This meant the invasion of Kyūshū alone would have resulted in 268,000 casualties. This number was similarly echoed by Intelligence Chief Maj. Gen. Charles Willoughby.
Some estimates were far higher. One study conducted during deliberations showed that the invasion of Japan would cause up to four million American casualties and around 10 million Japanese deaths. It was these figures that played a role in the decision to drop the atomic bombs.
Operation Ketsugō
As the US planned its invasion, Japan was busy fortifying its defenses. Recognizing the increasing likelihood of an Allied assault, Japanese officials anticipated an attack post-1945 typhoon season. Remarkably, they accurately guessed the invasion locations.
Japan readied itself to counter 90 Allied divisions—20 more than what was actually expected. By this time, Japan understood that victory was out of reach. Instead, the strategy was to inflict such heavy costs on the invaders that the Allies might consider a truce.
Operation Ketsugō, Japan’s resistance strategy, not only involved significant military forces but also mobilized civilians. An extensive training program was put in place for new troops, including frogmen, and 28 million men and women were prepared for the Volunteer Fighting Corps. Additionally, Japan intended to use kamikaze pilots to stop the Allied naval forces from reaching the shores.
Downfall of Operation Downfall
Ultimately, Japan’s preparations were for nothing, as its troops couldn’t withstand the attacks that brought World War II to a close. Before Operation Downfall could be put into action, the Americans dropped the atomic bomb Little Boy on Hiroshima, followed shortly after by Fat Man over Nagasaki. The Japanese surrender and the Soviet advance into Manchuria that followed solidified for the allies that Downfall was no longer needed.
Prior to this, the US really was actually preparing for the invasion. The country even went so far as to create almost 500,000 Purple Hearts in advance of the waves of injured Americans that would come out of Operation Downfall. Since they were never needed, the US military opted to hand out these medals in future wars; so many were made, in fact, that they were given out during the Korean War, in Vietnam, and during the wars in Iraq and Afghanistan.
As of 2020, it was believed there could be as many as 60,000 of these Purple Hearts yet to be given out.