What Was Operation Downfall?

Operation Downfall was a planned Allied invasion of the Japanese home islands near the end of World War II, which was halted when atomic bombs were dropped on Hiroshima and Nagasaki.

Feb 6, 2024By Matt Whittaker, BA History & Asian Studies

what was operation downfall


Operation Downfall during World War II consisted of two phases, Olympic and Coronet, intended to force Imperial Japan’s total capitulation. The first part, planned for November 1945, would start from occupied Okinawa. Not much remained of the Empire, but with Japan’s stubborn refusal to continue fighting, there seemed to be few options.


A Wrecked Perimeter

talented wwii soldier
A US Marine during the Battle for Okinawa, May 1945. Source: history.com


In the 1930s, Japan fortified key Mariana Islands like Saipan and Truk. The pace increased after 1943 as the tide turned. The bitter defeat at Guadalcanal ripped a critical hole in Japan’s island defense perimeter. Like dominos, these essential islands and others fell to the American island-hopping campaign, bypassing unimportant garrisons. By June 1945, Okinawa fell, only four hundred miles south of Kyushu, much to Japan’s horror.


The Silent Menace

Mt. Fuji 1943 via periscope USS Trigger Source: Navy History and Heritage Command
Mt. Fuji 1943 via periscope USS Trigger Source: Navy History and Heritage Command


American submarines helped to wreak havoc on Japan’s sea lanes, sinking nearly 56% of Japan’s shipping. Like Great Britain, the Empire’s survival depended on open sea lanes. American wolfpacks had been lurking in these sea lanes since late 1943, sinking many navy and merchant ships. By June 1945, the unrelenting submarine warfare nearly severed shipping to Japan’s Asian colonies. Even the Imperial Navy had a dozen destroyers remaining.


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The enormous shipping losses also sharply reduced oil, food, and war material shipments. Like many island nations, Japan needed to import food. Thus food allotments became increasingly rationed, with the daily calorie count cut to 1,800 per person. 


Japanese Preparations

Operation Olympic Map Source: U.S. Government Printing Office
Operation Olympic Map Source: U.S. Government Printing Office


By 1945, Japan’s government knew the war to be unwinnable but could not fathom unconditional surrender. Also, any resistance would have to inflict a ghastly number of casualties. The Japanese deduced southern Kyushu in late 1944 for any landings, quickly deploying their forces. At first, the Americans thought Japanese military strength would be 300,000 in June 1945. By August, the numbers rose to 900,000, plus thousands of suicide planes, ships, and fortifications. 


Phase One: Operation Olympic

B-29 Pacific Bomber dropping bombs over Japan. Source: National World War II Museum
B-29 Pacific Bomber dropping bombs over Japan. Source: National World War II Museum


Unlike D-Day in 1944, Operation Olympic would be only the first step. Planned for November 1, nearly 500,000 troops would land on Kyushu’s beaches. Next, these forces would occupy Kyushu’s southern half, preparing for Phase Two, Operation Coronet’s landings near Tokyo.


The Americans anticipated a high death toll for their troops, mainly from air attacks, miniature subs, and a fierce defense. During Okinawa, kamikazes and air attacks sank thirty-six ships, and most Japanese soldiers fought to the death. Losses just for Kyushu alone were estimated to hit 40,000. The total expected casualties for Operation Downfall might have reached 800,000. 


Phase Two: Operation Coronet

Map of Operation Downfall. Source: Wikimedia
Map of Operation Downfall. Source: Wikimedia


For February 1946, Coronet would include Allied troops rather than Olympic troops under American command. The schwerpunkt of Operation Downfall was Coronet, landing one million troops near Tokyo from Kyushu. Tokyo sits on the Kanto plain, the flattest part of the Home Islands. Here, the Allies’ mechanized and armored forces would move fast. 


Japanese terrain consisted of few beaches, mountains, and ridges that favored the defender. Also, Japan mobilized civilians to fight, giving many makeshift weapons or providing training on guerilla warfare. Throughout Operation Downfall, Marianna Island-based B-29s would bomb railroad yards, bases, and airfields. Fighter sweeps from Iwo Jima, Okinawa, and U.S. Navy carriers would be constant.


American Preparations

USS Iowa Source: Naval Heritage & Command
USS Iowa Source: Naval Heritage & Command


Douglas MacArthur would be in command of the planning of Operation Downfall. Also, since Germany surrendered, the swift transfer of forces from Europe began. Some units had already started training. Others gathered together the latest equipment – swapping B-17s for B-29 Superfortresses. For resupply, the Philippines and Hawaii became the supply hubs. 


Heavy bomber squadrons would be in the Philippines or on existing fields in the Marianas. Okinawa, bloodily taken in April 1945, would be a hub too for fighters and ground attack aircraft. About forty divisions would be deployed, including Allied ones. The naval support for Downfall included forty-two carriers, two dozen battleships, and hundreds of other ships. This would have been the world’s biggest fleet ever assembled.


An Atomic Ending

VJ Day Source: U.S. Department of Energy
VJ Day Source: U.S. Department of Energy


Despite the planning, concern grew over the cost in lives. The war-weary U.S. would not bear massive casualties after four years of war. Okinawa proved Japan would fight bitterly. The dreaded kamikazes sank or damaged 400 ships and 12,000 dead. American intelligence determined that there were 2,500 kamikazes near Kyushu, plus thousands more nearby.


President Truman decided to use the Manhattan Project’s A-bomb. On August 6, the first bomb incinerated Hiroshima; the President asked for Japan’s surrender. Only after the second bomb destroyed Nagasaki did Japan capitulate on August 15.


Operation Downfall became unnecessary. Besides American lives, the planners reckoned that civilians by the thousands would perish. Truman’s decision to permit the bomb divided many after the war, debating if such use was ever necessary.

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By Matt WhittakerBA History & Asian StudiesMatt Whittaker is an avid history reader, fascinated by the why, how and when. With a B.A. in History and Asian Studies from University of Massachusetts, he does deep dives into medieval, Asian and military history. Matt’s other passion besides family is the long-distance Zen-like runs.