Operation Downfall

• 1. The Invasion That Never Was

  ›

  Operation Downfall was the proposed plan by United States and British Commonwealth forces for the invasion of the Japanese home islands near the end of World War II. It was canceled when Japan surrendered following the atomic bombings of Hiroshima and Nagasaki, the Soviet declaration of war, and the invasion of Manchuria. The operation had two parts: Operation Olympic and Operation Coronet. Set to begin in November 1945, Operation Olympic was intended to capture the southern third of the southernmost main Japanese island, Kyūshū, with the recently captured island of Okinawa to be used as a staging area. In Spring 1946 would come Operation Coronet, the planned invasion of the Kantō Plain, near Tokyo, on the main Japanese island of Honshu. Airbases on Kyushu captured in Operation Olympic would allow land-based air support for Operation Coronet. If Downfall had taken place, it would have been the largest amphibious operation in history, surpassing D-Day.

• 2. Commanders And Rivalries

  ›

  Responsibility for the planning of Operation Downfall fell to American commanders Fleet Admiral Chester Nimitz, General of the Army Douglas MacArthur and the Joint Chiefs of Staff, Fleet Admirals Ernest King and William D. Leahy, and Generals of the Army George Marshall and Henry H. Arnold (the latter being the commander of the U.S. Army Air Forces). At the time, the development of the atomic bomb was a very closely guarded secret, known only to a few top officials outside the Manhattan Project (and to the Soviet espionage apparatus, which had managed to infiltrate or recruit agents within the program, despite the tight security around it), and the initial planning for the invasion of Japan did not take its existence into consideration. Once the atomic bomb became available, General Marshall envisioned using it to support the invasion if sufficient numbers could be produced in time. The Pacific War was not under a single Allied commander-in-chief (C-in-C). Allied command was divided into regions: by 1945, for example, Chester Nimitz was the Allied C-in-C Pacific Ocean Areas, while Douglas MacArthur was Supreme Allied Commander, South West Pacific Area, and Admiral Louis Mountbatten was the Supreme Allied Commander, South East Asia Command. A unified command was deemed necessary for an invasion of Japan. Interservice rivalry over who it should be (the United States Navy wanted Nimitz, but the United States Army wanted MacArthur) was so serious that it threatened to derail planning. Ultimately, the Navy partially conceded, and MacArthur was to be given total command of all forces if circumstances made it necessary.

• 3. Olympic And Coronet Stages

  ›

  Operation Olympic, the invasion of Kyūshū, was to begin on "X-Day", which was scheduled for the 1st of November 1945. The combined Allied naval armada would have been the largest ever assembled, including 42 aircraft carriers, 24 battleships, and 400 destroyers and destroyer escorts. Fourteen U.S. divisions and a "division-equivalent" (two regimental combat teams) were scheduled to take part in the initial landings. Using Okinawa as a staging base, the objective would have been to seize the southern portion of Kyushu. This area would then be used as a further staging point to attack Honshu in Operation Coronet. Operation Coronet, the invasion of Honshu at the Kantō Plain south of the capital, was to begin on "Y-Day", which was tentatively scheduled for the 1st of March 1946. Coronet would have been even larger than Olympic, with up to 45 U.S. divisions assigned for both the initial landing and follow-up (by comparison, the invasion of Normandy deployed twelve divisions in the initial landings). In the initial stage, the First Army would have invaded at Kujūkuri Beach, on the Bōsō Peninsula, while the Eighth Army invaded at Hiratsuka, on Sagami Bay; these armies would have comprised 25 divisions between them. Later, a follow-up force of up to twenty additional U.S. divisions and up to five or more British Commonwealth divisions would have landed as reinforcements.

• 4. Ketsugō And Total Resistance

  ›

  Meanwhile, the Japanese had their own plans. Initially, they were concerned about an invasion during the summer of 1945. However, the Battle of Okinawa went on for so long that they concluded the Allies would not be able to launch another operation before the typhoon season, during which the weather would be too risky for amphibious operations. Japanese intelligence predicted fairly closely where the invasion would take place: southern Kyushu at Miyazaki, Ariake Bay and/or the Satsuma Peninsula. Unlike the Germans, who were fooled about the Normandy landings, the Japanese accurately predicted the location and timing of the planned invasion before the United States decided them. The Japanese plan for defeating the invasion was called ("Operation: Decisive" or "Final Battle"). The Japanese planned to commit the entire population of Japan to resisting the invasion, and from June 1945 onward, a propaganda campaign calling for "The Glorious Death of One Hundred Million" commenced. The main message of "The Glorious Death of One Hundred Million" campaign was that it was "glorious to die for the holy emperor of Japan, and every Japanese man, woman, and child should die for the Emperor when the Allies arrived." Although it was not realistic that the entire Japanese population would be killed off, both American and Japanese officers at the time predicted a Japanese death toll in the millions.

• 5. Projected Casualties And Human Cost

  ›

  Due to the nature of combat in the Pacific Theater and the characteristics of the Japanese Armed Forces, it was accepted that a direct invasion of mainland Japan would be very difficult and costly. The Allies would not only have to contend with all available Japanese military forces that could be brought to bear, but also the resistance of a "fanatically hostile population." Depending on the scope and context, casualty estimates for American forces ranged from 220,000 to several million, and estimates of Japanese military and civilian casualties ran from the millions to the tens of millions. Casualty estimates did not include potential losses from radiation poisoning resulting from the tactical use of nuclear weapons or from Allied POWs who would have been executed by the Japanese. In the aftermath of the Marianas Campaign, the Joint Chiefs of Staff (JCS) revised their planning document, "Operations against Japan subsequent to Formosa" (JCS 924), to reflect the experience gained. Taking into account the stiff resistance of the Japanese 31st Army at Saipan, they concluded that if U.S. forces had to defeat all 3.5 million Japanese soldiers who could be made available, "it might cost us half a million American lives and many times that number wounded." Despite the high numbers, by the spring of 1945 a figure of 500,000 battle casualties for the projected invasion was widely used in briefings, while totals of closer to a million were used for actual planning purposes.

• 6. Soviet Invasion Of Hokkaido

  ›

  Unknown to the Americans, the Soviet Union also considered invading a major Japanese island, Hokkaido, by the end of August 1945, which would have put pressure on the Allies to act sooner than November. At the Yalta Conference (February 1945), the Allies had agreed that the Soviet Union would take the southern part of the island of Sakhalin, which Japan had invaded during the 1904, 1905 Russo-Japanese War, and which Russia had ceded in the Treaty of Portsmouth after the war (the Soviets already controlled the northern part), and the Kuril Islands, which had been assigned to Japan in the 1875 Treaty of St. Petersburg. On the other hand, no agreement envisaged Soviet participation in the invasion of Japan itself. The Soviets, however, had fewer than 400 ships, most of them not equipped for amphibious assault, when they declared war on Japan on the 8th of August 1945. For Operation Downfall, the US military envisaged requiring more than 30 divisions for a successful invasion of the home islands. In comparison, the Soviet Union had about 11 divisions available, comparable to the 14 divisions the US estimated that it would require to invade southern Kyushu. The Soviet invasion of the Kuril Islands (August 18 , the 1st of September 1945) took place after Japan's capitulation on August 15.