Operation Downfall
Operation Downfall was the overall Allied plan for the invasion of Japan at the end of World War II. It was scheduled to occur in two parts - Operation Olympic, the invasion of Kyushu; and later Operation Coronet, the invasion of Honshu near Tokyo. Following the atomic bombing of Hiroshima and Nagasaki, and the Soviet declaration of war against Japan, the Japanese surrendered and the operation was cancelled.
Operation Downfall
| Table of contents |
|
2 Olympic 3 Coronet 4 Estimated Casualties 5 External links and references |
Responsibility for planning the operation fell to the American commanders; Admiral of the Fleet Chester Nimitz, General of the Army Douglas MacArthur and the Joint Chiefs of Staff - Admirals of the Fleet Ernest King and William Leahy, and Generals of the Army George Marshall and Hap Arnold - who controlled the Twentieth Air Force, the strategic bombers. At the time, the development of the atomic bomb was a very closely guarded secret, known only to a few top officials, and planning for the invasion did not take its existence into consideration.
The navy urged the use of blockade and airpower to bring about Japan's capitulation. They suggested operations to capture airbases in nearby Shanghai, China and in Korea. These locations would give the army airforce a series of forward airbases from which to operate against Japan. The army, on the other hand, argued that such a strategy could prolong the war indefinetely and expend lives needlessly, and therefore that an invasion was necessary. They supported mounting a large-scale thrust directly against the Japanese homeland, with none of the side operations that the navy had suggested. Ultimately, the Army's viewpoint won out.
Although chemical warfare had been outlawed by the Geneva Protocol, neither the United States or Japan were signatories at the time. While the US had promised never to initiate gas warfare, earlier in the war Japan (allegedly) had used them against the Chinese in Manchuria. This gave the US a reason for their use.
"Fear of Japanese retaliation (to chemical weapon use) lessened because by the end of the war Japan's ability to delivery gas by air or long-range guns had all but disappeared. In 1944 Ultra revealed that the Japanese doubted their ability to retaliate against US use of gas. 'Every precaution must be taken not to give the enemy cause for a pretext to use gas,' the commanders were warned. So fearful were the Japanese leaders that they planned to ignore isolated tactical use of gas in the home islands by the US forces because they feared escalation." (John Ray Skates, The Invasion of Japan, ISBN 0-87249-972-3)
However, for the defense of Kyushu during Olympic, the Japanese intended to revert to the tactic of defense on the beaches. The Japanese intended to repel the invasion, not just attrite it. Using defense in depth, repeling the invasion would require troop mobility. Transit and communication systems (roads, rail, telephone) on Kyushu prior to the invasion were poor, and American air-power would destroy what little did exist very quickly. The only concievable way the Japanese could repel the invasion would be to stop the American attack at the beaches.
In prior combat against the Japanese, MacArthur's forces had a kill ratio of twenty-two Japanese for every American, and a injury ratio of five Japanese per American. Unlike in previous operations, the Kanto plain would lend itself well to American mobility, and increase the ratio further in favor of the Americans.
MacArthur's staff made the following estimates about American casualties for Olympic:
These estimates roughly coincide with the casualties suffered during the D-Day campaign, which had sustained 63,360 casualties in the first forty-eight days. (John Ray Skates, The Invasion of Japan, p.79)
However, the two previous campaigns in the Pacific had seen higher American casualties to Japanese casualties compared to those before. Okinawa saw 12,000 US deaths, 5,000 of which were suffered by the Navy, and 72,000 casualties in total against Japanese casualties of 110,000. Iwo Jima actually saw more American casualties than Japanese, the only major land battle of the Pacific where that occured.
Given the Japanese predeliction for fanatical resistance, the fact that Japanese civilians were being encouraged to become suicide attackers, and the enormous number of Japanese troops to be faced, high casualties were seen to be inevitable. If the figures of Okinawa were repeated, then American casualties of over one million were not out of the question, since well over that many Japanese troops were present in the home islands. If the figures of Iwo Jima were repeated, then casualties would have been even higher.
Planning
Considerations
The primary considerations that the planners had to deal with were time and casualties - how could they force Japan's surrender as quickly as possible, with as few Allied casualties as possible? In 1943, the Joint Chiefs agreed that Japan should be forced to surrender not more than one year after Germany's surrender. They were inspired to do this after seeing British-made plans that did not call for invasion of the home islands until the fall of 1947. Prolonging the war to such an extent was considered dangerous for national morale. Japanese Terrain
Physically, Japan made an imposing target. It has few beaches suitable for invasion. Only Kyushu (the southernmost island of Japan) and the Kanto plain (just outside of Tokyo) made suitable invasion zones. The allies decided to launch a two-pronged invasion. Operation Olympic would attack Kyushu in the South. Airbases would be established, and those would give cover for Operation Coronet, the attack on Tokyo bay. This was obvious to the Japanese as well, who were able to accurately guess the strength and locations of the Allied invasions, and began to reinforce those areas as early as 1944.Operational Command
Throughout the war, unlike in the European theatre of operations, the army and the navy were unable to agree on a single theatre commander. Instead, the Pacific was divided up into regions. Chester Nimitz was commander of the central pacific, while Douglas MacArthur was commander of the South Pacific. For an invasion of Japan, a unified command was deemed necessary. Inter-service squabbling over who it should be - the navy wanted Nimitz while the Army wanted MacArthur - was so serious that it threatened to derail planning. Ultimately, the navy partially conceeded and MacArthur was to have total command of all forces, if circumstances made it necessary.Olympic
Operation Olympic, the invasion of Kyushu, was to begin November 1, 1945. Fifteen divisions were scheduled to take part in this landing. The naval armada would have been the largest ever assembled, including forty-two aircraft carriers, twenty-four battleships and almost four hundred destroyers and destroyer escorts. Using Okinawa as a staging base, Olympic was to seize the southern portion of Kyushu, to use as a staging point. It was also to include a deception plan, known as Operation Pastel. See also Ten Ichi and Majestic.Chemical Weapons Use
Because of a known buildup of Japanese troups on Kyushu leading up to the invasion, some American military planners proposed the use of chemical weapons prior to or during the invasion. Because of its predicatable wind patterns and several other factors, Japan was particularly vulnerable to gas attack. Such attacks would neutralize the Japanese tendency to fight from caves - caves would only increase the soldiers' exposure to gas. The Japanese Defense
In any amphibious operation, the defender has two choices for defensive stategy - strong defense of the beaches, or defense in depth. Early in the war (such as at Tarawa) the Japanese employed strong defenses on the beaches themselves, with little or no manpower in reserve. This tactic proved to be very vulnerable to pre-invasion shore bombardment. Later in the war, at Iwo Jima and Okinawa, the Japanese switched strategy and employed defense-in-depth. Fighting degenerated into attrition-warfare. This led to very high casualties on both sides, which the Americans were unused to. Coronet
Operation Coronet, the invasion of Honshu at the Tokyo Plain south of the capital, was set to begin on December 1, 1945. This was later postponed to March, 1946. Coronet would have been the largest amphibious operation of all time, with fifteen divisions (including the floating reserve) earmarked for the operation.Redeployment from Europe
Olympic was to be mounted with with resources already in the theatre. If reinforcements had been needed, they could have been provided out of the forces being assembled for Coronet. However, Coronet would have needed substantial forces from Europe. Those would have included the US First Army and Eighth Air Force, Royal Air Force Bomber Command units operating from Okinawa as the Tiger Force, and, British, Australian and New Zealand ground troops.Estimated Casualties
After the war, in their justification to use the Atomic bomb, Harry Truman, Henry Stimson, and Winston Churchill all claimed that the invasion of Japan would could cost in excess of a million allied casualties. Official sources for these claims have never been shown.
Of these, roughly a fourth would be fatalities. External links and references