Operation Downfall — The Campaign to Conquer Japan Would Have Dwarfed the D-Day Landings

The plan to invade the Japanese home islands in 1945 and 1946 would have been the deadliest campaign in military history costing nearly 1 million Allied dead and up to 10 million Japanese.

The plan to invade the Japanese home islands in 1945 and 1946 would have been the deadliest campaign in military history costing nearly 1 million Allied dead and up to 10 million Japanese.

“The U.S. military, expecting the resistance of a ‘fanatically hostile population’, were making preparations for between 1.7 and 4 million casualties.”

IT COULD BE called the world’s greatest battle… that never happened.

Operation Downfall, the codename for the U.S.-led mission to capture the Japanese homeland in 1945 and 1946 never did take place. Had the invasion not been preempted by the dropping of the atom bombs on Hiroshima and Nagasaki, almost all agree that the campaign would have stood as the bloodiest chapter of the Second World War, adding as much as an additional 10 million dead to the war’s already mind-boggling final body count of 50 million.

Details of Downfall.

Downfall was the brainchild of Admiral Chester Nimitz and generals Douglas MacArthur and George Marshall. It was comprised of TWO mammoth amphibious operations. The first phase, dubbed Operation Olympic was planned as a November, 1945 assault on the southernmost Japanese home island of Kyushu.

Phase two, Operation Coronet, was to kick off in March 1946 and would have involved a series of landings on the island of Honshu that were intended to put Allied ground forces within reach of Tokyo.

As many as 42 aircraft carriers were being marshalled for the invasion of Japan. (Image source: WikiCommons)


The Olympic plan included 14 army divisions in the initial landings alone, supported by an armada of 400 destroyers, 24 battleships and a staggering 42 aircraft carriers. The invasion force itself would hit 35 landing beaches that ringed the southern third of the island, all codenamed for cars: Buick, Cadillac, Stutz, etc. Overhead, aircraft from the Twentieth, Fifth, Seventh and Thirteenth air forces would pulverize Japanese airfields, communication lines and troop concentrations, while the guns of the naval forces would demolish coastal defences. Supporting the operation would be a British Commonwealth fleet comprising the entire Pacific arm of the Royal Navy, which included up to 18 aircraft carriers and four battleships.

Once Operation Olympic had secured the southern portion of Kyushu, the stage would be set for the even larger second phase, Coronet.

Britain’s Bomber Command was ready to contribute to the Allied effort to overrun the Japanese home islands. (Image source: Imperial War Museums)


Scheduled for March, 1946 the landings on Honshu would use forces already committed along with significant numbers of fresh troops brought over from Europe. A Commonwealth corps would include units from Australia, Britain and Canada. Aircraft from the RAF’s Bomber Command would also be redeployed from Europe for the final push. All in all, Coronet would dwarf Olympic, using 25 army divisions in the initial assault alone – that’s more than twice the number of divisions committed in Operation Overlord in 1944.

The Japanese anticipated the objectives of the Allied invasion plans, although the leadership expected the blow to fall in the summer of 1945 immediately after the capture of Okinawa.

Japanese school girls train with rifles. Armed civilians would aid in the defence of the home islands. (Image source: WikiCommons)

Strategy for Defence

The Japanese plan for this final battle was dubbed Ketsugo or “Decisive”.

While nearly four years of war had seen the Japanese fleet decimated, the Emperor’s forces planned to throw their remaining six carriers, four cruisers and one battleship, along with 350 midget submarines, 400 manned torpedoes and 800 suicide speed boats into action against the Allied armada.

On the ground, Japan had a total of 900,000 troops formed into 65 divisions, although it only had weapons and ammunition for between 30 and 40 divisions. Almost all of these would be committed to the defense of Kyushu. Supporting the troops would be a 28-million-strong ad hoc militia army called the Patriotic Citizens Fighting Force. This was made up of all healthy males between the ages of 15 and 60 and women aged 17 to 40. These formations would go into battle almost completely unarmed. Many civilians were issued surplus rifles, antique muskets, bows and even sharpened bamboo pikes.

Japan’s air force would rely heavily on its Kamikaze pilots. More than 10,000 were expected to be used, primarily against troop transport ships.

U.S. commanders were expecting a protracted campaign that would last well into 1946 or beyond. (Image source: WikiCommons)

Worst Case Scenarios

Both sides braced for heavy casualties. The U.S. military, expecting resistance by a “fanatically hostile population,” made preparations for between 1.7 and 4 million casualties with up to 800,000 dead. Between 5 and 10 million Japanese deaths were projected.

The Japanese leadership had no illusions that this final act of resistance would somehow lead to victory, but many in the high command were optimistic that a spirited defence might compel the Allies to negotiate a favourable peace rather than spend the resources and lives in such an epic fight.

Japanese representatives on board the USS Missouri in Tokyo Bay to participate in formal surrender ceremonies on Sept. 2, 1945. (U.S. Air Force photo)


Fortunately, Downfall never happened. The two atom bombs, dropped nearly four months before the invasion was to begin, brought the war to a swift conclusion. While the attacks on Hiroshima and Nagasaki cost the lives of upwards of 250,000 Japanese civilians, historians agree that a protracted ground campaign would have killed millions.

(Image source: WikiCommons)

Did you know…

Here are some remarkable facts about Operation Downfall:

  • The Japanese homeland was going to be bitterly contested. Both side expected the other to resort to poison gas, yet neither had plans to use chemical weapons.
  • The U.S. plan called for the assistance of British and Canadian troops brought in from the European theatre and a force of Australians. To ensure interoperability, MacArthur insisted that these units be trained in the U.S. in the months leading up to Coronet. Additionally, the Allied divisions would fight under a U.S.-style corps structure and the general wanted them to only use American equipment.
  • MacArthur rejected the suggestion that a contingent of Indian troops be included in the order of battle, citing the language barrier as the main sticking point.
  • The Manhattan Project was so secret that few involved in the planning of Downfall initially even knew of its existence. As details of the atom bombs were revealed in mid-1945, the invasion planners actually anticipated using the weapons to directly support ground combat. In fact, the Pentagon planned for up to seven nuclear bombs to be available for use in the campaign.
  • Expecting heavy casualties, the U.S. military ordered the production of half a million Purple Heart citations in 1945. Since the war ended before the invasion, the American military put the medals into storage and has drawn from this stockpile in every war since then. There are still nearly 100,000 Purple Hearts in U.S. inventory left over from the production run prior to Downfall.

(Originally published on June 1, 2012)

11 comments for “Operation Downfall — The Campaign to Conquer Japan Would Have Dwarfed the D-Day Landings

  1. 1 June, 2012 at 4:15 pm

    Our most popular post so far. Wow!

  2. 3 June, 2012 at 5:46 am

    Interesting blog! I’ll definitely drop by more often.
    It would have been nice if you included a little map of Japan showing troop concentrations and movements, to make the plans a bit more visual. Other than that, good, well-written post.

  3. 3 June, 2012 at 5:17 pm

    Hi Paperfold: Thanks for the comments. I appreciate your interest. Here’s a link to a map that shows some of the battle plan. http://www.kilroywashere.org/006-Pages/Invasion.html

  4. 13 June, 2012 at 2:02 pm

    No one can really say for sure the invasion(s) would have occurred – atomic bombs or not. One influence that may have a place here was the public sentiment back at the homefront. It is reported by experts (such as yourself) that MacArthur was seeking glory. On the other hand, if it weren’t for MacArthur, the Occupation of Japan may have gone terribly wrong.

    As a matter of historical interest and in relation to one of your points, my grandmother did undergo training with a bamboo spear in Tokyo. The instructor was an older retired Army man.

    • 13 June, 2012 at 2:10 pm

      Thanks again for the post. Amazing story about your grandmother!

  5. vcranham
    17 July, 2012 at 7:28 am

    My father, in British RN , was headed to Japan, for a 5 year tour of duty as part of operations Olympic and Downfall. His ship was in, Indian Ocean when Japan surrendered and the mission became one of occupation, instead.
    He and another sailor were called to the captain’s office, and given the choice of carrying on to Japan with ship, or picked up by tender sent out from Madras – to make their own way back to England.
    No easy feat, as the Allied Fleet would all now be headed to Japan, if not still part of European theatre ! As the two longest serving sailors on board, they were given
    first chance to go home…

  6. Harland
    15 February, 2014 at 12:35 pm

    As late as surrender time-even after the A-bombs had been dropped-a staff lieutenant colonel, related to the War Minister himself, was fervently convinced that even if the whole Japanese race were all but wiped out, its determination to preserve the National Polity would be forever recorded in the annals of man; whereas a people who sacrificed their will upon the altar of physical existence could never deserve resurrection. It would be useless for the people to survive the war, anyhow, if the structure of the State itself were destroyed. It was better to die than to seek ignominious “safety”.

    At a climactic last Imperial Conference, War Minister Anami was still talking about going on with the war, of meting out a terrible blow to the enemy and achieving a good opportunity to end the war. Japan must press forward courageously, seeking Life in Death: certain victory was not assured, but neither was utter defeat. The terrain was working in favor of the defenders, and so was the inflexible national unity. But just in case a massive blow against the enemy proved not possible, it seemed appropriate for the name of Nippon to be inscribed forever in history by the annihilation of her 100 million loyal subjects, etc., etc. And tears welled into the eyes of the earnest War Minister.

    When the Emperor, by a thrilling act of personal courage, opted for peace-and surrender-he too was weeping. He reminded his stunned auditors that ever since the outbreak of the war there had been frequent cases when Army and Navy actions differed from plans. Now the armed forces were preparing for decisive battle in the homeland and were claiming that the prospects of victory were satisfactory.

    He was profoundly troubled, continued the Emperor. What would happen if Japan plunged into decisive battle under such circumstances? The entire race would be obliterated, and this would be a betrayal of the trust of ancestors and the duty toward posterity, lest Japan never again rise. Continuation of the war, then, could only serve to cripple Japan, extinguish civilization, and bring misfortune to mankind.

    The Japanese Emperor’s decision to end the war, under enormous external and internal pressure, obviated the American landings and the hemorrhage that was bound to occur soon on the beaches of Miyazaki, Satsuma, and Ariake. Not only would five US ground divisions, etc., be saved from the destruction at sea which the Japanese resolutely promised them, but untold thousands of Japanese would not die either-such as squadrons of kamikaze pilots and sailors with one way tickets to the shrine of heroes at Yasukuni; or the women and children clutching pitiful staves and bamboo spears.

    — Dr. Alan C. Coox, “Olympic vs. Ketsu-Go”, Marine Corps Gazette, August 1965, Vol. 49, No. 8.

  7. Rob Bolvin
    18 December, 2014 at 11:39 pm

    My mother was 10 in 1945, living in Yanai, Japan, and was being taught to use a bamboo spear also. She was told to run toward American soldiers with a grenade in her hands rather than throwing it, since she couldn’t throw very well. One day she saw a flash over the hills to the northeast, it was the Hiroshima bomb. I’ve always believed Fat Man and Little Boy saved her life.

    • admin
      18 December, 2014 at 11:42 pm

      Amazing story! Thanks for telling us.

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