The Pacific War Online Encyclopedia: Downfall (original) (raw)

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U.S. Army. Via ibiblio.org

DOWNFALL was the plan for the Allied invasion of Japan. It was never set in motion, since the Japanese capitulatedon 15 August 1945 on the basis of the Potsdam Declaration. The Japanese surrender followed the collapse of the Japanese economy under blockade, the nuclear attackson Hiroshima and Nagasaki, and the Russian intervention on 9 August 1945. Defenders of Truman'sdecision to use nuclear weapons have long pointed to DOWNFALL and its enormous casualty projections as the likely alternative.

DOWNFALL was to take place in two stages. The first, OLYMPIC, was to be an invasion of southern Kyushu on 1 November 1945. MacArthur's planners expected to land 6 Armywith twelve divisions (plus two in reserve), which would make three separate landings. Opposition was expected to be limited to three divisions in southern Kyushu and three more in northern Kyushu. Once beachheads had been consolidated and airfields put in operation, MacArthur would carry out CORONET, the invasion of the Tokyo region on Honshu.

The projected date for CORONET was 1 March 1946, and the operation would be carried out by 8 and 10 Armies with a total of fourteen divisions. These would be joined later by 1 Army with ten more divisions. Four more divisions were to be held in reserve.

However, following the defeat of Germany, the American public had become very war-weary, and Congress had directed the Army to reduce its manpower by a million men as quickly as possible. The Army chose to implement a "point" system to ensure that those who had served longest (as measured by their Adjusted Service Rating) were discharged first. This stripped the most experienced officersand men out of many units. The worst case, 45 Division, lost 83 percent of its manpower. It would take six months to retrain some of the units that were redeployed from Europe to participate in CORONET. The Learned-Smith Report advocated increasing inductionof new manpower, to a level that works out to about 63,700 a month, in order to supply replacements to the forces deployed against Japan.

Production was expected to shift dramatically after the German defeat. Shipbuildingwould drop back to 1943 levels, and production of the M4 Sherman tankwould cease in June 1945. However, production of new models of aircraftand other equipment was to increase. In addition to improved versions of the P-51 Mustang and P-47 Thunderbolt, production would gear up for the new P-80 Shooting Star jet fighter, the FR-1 Fireball, the F8F Bearcat, and the F7F Tigercat, while the Sherman would be supplanted by the M26 Pershing.

Casualty projections for DOWNFALL varied wildly. This was not a sign of bad faith on the part of planners, but a reflection of the extreme uncertainties inherent in the projections themselves. The casualty projections settled on by the Joint Staff Planners and placed before Truman were for a total of 193,500 casualties, including 43,500 dead, in OLYMPIC and CORONET. Other estimates went as low as 105,050 total casualties or as high as 200,000 casualties for OLYMPIC alone. These are Allied casualty projects: It seems to have been tacitly assumed that all but a few of the 350,000 Japanese defenders thought to be on Kyushu would be killed.

Frank (in Marston 2005) has pointed out that Allied fears of the likely cost of DOWNFALL were exceeded by their fears that there would be no organized capitulation. The Joint Chiefs of Staff concluded in an April 1945 policy paper that, since no organized Japanese unit of any size had ever surrendered, it was quite possible that the Japanese government would never surrender or a surrender would be ignored by the military, leaving "no alternative to annihilation" of the entire 4 to 5 million men of the Japanese Army scattered throughout Japan, the Pacific and east Asia.

The Japanese Defense Plan: KETSU-GO

MacArthur had a bad habit of underestimating his opposition, and OLYMPIC was no exception. Frank (1999) has argued that a factor in Truman's decision to employ nuclear weapons was intelligence showing that the Japanese were building up their forces in Kyushu far more rapidly than anticipated. This multiplied the risks of the invasion while suggesting the Japanese were far from ready to surrender.

Japanese leaders had already concluded as early as January 1945 that an Allied invasion of Japan was inevitable. The inner defense zone (Formosa, Iwo Jima, Okinawa, Shanghai and South Korea) was to be stubbornly defended to buy time and wear down the Allied forces, but would receive no further reinforcements. The final decisive battle would be fought on the home islands themselves.

The Japanese had concluded that if they could inflict enough casualties on the invading Allies, they could force the Allies to negotiate peace terms. There was no possibility of the Americans achieving strategic surprise. Iwo Jima lacked the room to base huge air forces, leaving only Okinawaas a possible base for air operations covering the invasion. Allied fighters operating out of Okinawa could reach only as far as southern Kyushu, and from there it was a simple matter for Japanese strategists to identify the possible landing beaches.

The Japanese defense strategy rejected defense in depth, calling instead for mass kamikazeattack on the invasion convoys, followed by a maximum effort by land forces on the beaches. These forces consisted mostly of static coastal divisions, which were to engage the Americans so closely that the Americans would be unable to make full use of their overwhelming firepower. Each static division was assigned a "counterattack regiment" to carry out immediate local counterattacks. Behind the beaches, the Japanese planned to deploy "mobile decisive-battle divisions" to counterattack any Allied breakthroughs. Training of all divisions was to be completed by July 1945. Ariake Bay was seen as the most likely invasion point, and Japanese deployments were made accordingly.

There still remained the problem of the prelanding bombardment. The Japanese coastal regiments were instructed to deploy a single platoon each on beachfront positions in the dunes a kilometer from the beach. One or two kilometers further back, each coastal regiment deployed about three companies in the "advanced frontal area." Four or five kilometers from the water was the main line of resistance. Fortificationswere constructed at night to foil reconnaissance and were nearing completion by August 1945.

Army officers, from Anami on down, almost universally believed that Ketsu-Gowould be successful and would force the Allies to settle for a negotiated peace.

Allied Detection of Preparations for KETSU-GO

Allied intelligence began picking up the preparatios for Ketsu-Go in July 1945. By July 25 the scope of these preparations were clear and alarming to Allied planners. At about the same time, Toyodaand his deputy, Ozawa, were given supreme command of all remaining naval forces. Allied intelligence officers interpreted this as evidence of a more aggressive naval command that was likely to cooperate with the most extreme Army officers. Photoreconnaissance of the 243 known airfields in the Japanese Home Islands revealed an air strength of 8,010 aircraft, far exceeding earlier estimates. By the time of the surrender, this estimate had grown to 10,290 aircraft.

Frank (in Marston 2005) has concluded that, as a result of this radio intelligence, DOWNFALL was on the way to being canceled by the second week of August 1945 and planners had begun to consider a landing in northern Honshu instead.

Allied order of battle, OLYMPIC

| Allied Forces, Pacific (MacArthur) | | | | | --------------------------------------------------------------------------- | ---------------------------------------------------------------- | -------------------------------------------------------------------------- | | | | 6 Army (Krueger) | | | | | | | 40 Division (Myers) | Detached from 9 Corps to seize small islands south of Kyushu on X-5 to X-4 | | | | | 158 Regimental Combat Team | Tanegashima on X-5 | | | | | 1 Corps (Swift) | Miyazaki | | | | | | 25 Division | | | | | | 33 Division | | | | | | 41 Division | | | | | | 2 tank battalions | | | | | | 1 tank destroyer battalion | | | | | 11 Corps (Hall) | Ariake Bay | | | | | | 1 Cavalry Division | | | | | | Americal Division | | | | | | 43 Division | | | | | | 112 Cavalry Regiment | | | | | | 2 tank battalions | | | | | | 1 tank destroyer battalion | | | | | 5 Amphibious Corps (Schmidt) | Sendai | | | | | | 2 Marine Division | | | | | | 3 Marine Division | | | | | | 5 Marine Division | | | | | 9 Corps (Ryder) | Army reserve | | | | | | 77 Division | | | | | | 98 Division | | | | | | 2 tank battalions | | | | | | 1 tank destroyer battalion | | | | | 11 Airborne Division (Swing) | Army reserve | |

Japanese order of battle, OLYMPIC

References
Frank (1999)

Marston (2005)

Morison (1959)

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