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DOWNFALL


Chart of proposed landings and feints for DOWNFALL

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 capitulated on 15 August 1945 on the basis of the Potsdam Declaration. The Japanese surrender followed the collapse of the Japanese economy under blockade, the nuclear attacks on Hiroshima and Nagasaki, and the Russian intervention on 9 August 1945. Defenders of Truman's decision 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 Army with 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 officers and 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 induction of 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. Shipbuilding would drop back to 1943 levels, and production of the M4 Sherman tank would cease in June 1945. However, production of new models of aircraft and 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 surpriseIwo Jima lacked the room to base huge air forces, leaving only Okinawa as 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 kamikaze attack 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. Fortifications were constructed at night to foil reconnaissance and were nearing completion by August 1945.

Army officers, from Anami on down, almost universally believed that Ketsu-Go would 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, Toyoda and 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

16 Area Army (Nishihara)     


216 Division (Nakano)
Area Army reserve

107 Independent Mixed Brigade (Futami)
Goto Islands

118 Independent Mixed Brigade (Uchiyama)     
Bungo Strait

122 Independent Mixed Brigade (Taniguchi)
Nagasaki

126 Independent Mixed Brigade
Amakusa Islands
 
56 Army (Shichida)
northern Kyushu

 
57 Division (Yano)
First class division


145 Division (Ohara)



312 Division (Tada)
Static coastal division


351 Division (Fujimura)     
Static coastal division


124 Independent Mixed Brigade (Ishii)     



4 Tank Brigade



46 Tank Regiment


57 Army (Nishihara)      southern Kyushu


25 Division (Kato)
First class division


86 Division (Yoshinaka)
First class division. Ariake Bay


 
98 Independent Mixed Brigade (Kurosu)    
First class. Osumi Peninsula



364 Independent Regiment




3 independent battalions



154 Division (Futami)
Static coastal division. Miyazaki area


156 Division (Higushi)
Static coastal division. Miyazaki area


212 Division (Sakurai)
Counterattack division. Miyazaki area


109 Independent Mixed Brigade
Tanegashima. 5901 men.


5 Tank Brigade
56 medium tanks, 26 light tanks, 30 "gun" tanks, 6 sel-propelled guns


6 Tank Brigade
Less 37 Tank Regiment, detached for service with 40 Army

40 Army (Nakazawa)
Satsuma Peninsula. Suffered from serious lack of supplies and equipment.


77 Division (Nakayama)
First class division


146 Division (Tsuboshima)
southern Satsuma Peninsula


206 Division (Iwakiri)
Counterattack division. Western Satsuma Peninsula


303 Division (Ishida)
Coastal defense division with virtually no weapons


125 Independent Mixed Brigade (Kurahashi)
Lacked about a third of its heavy weapons


37 Tank Regiment


References
Frank (1999)

Marston (2005)

Morison (1959)

Stern (2010)


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