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Olympic vs. Ketsu-Go

Marine Corps Gazette, August 1965, Vol. 49, No. 8.

Dr. K. Jack Bauer describes the United States' plans to assault Kyushu in the fall of 1945, a preliminary to the more massive invasion of Honshu.

Dr. Alan C. Coox authored the italicized portion of the following article, an account of the Japanese plan to defend Kyushu.

"Hell was upon us, when we lost Saipan," the Chief of the Japanese Naval General Staff told American interrogators shortly after the war. A high-ranking NGS planner explained: "After the Coral Sea and Midway, I still had hope. After Guadalcanal, I felt we could not win, only we would not lose. After the Marianas, we had little chance. After Okinawa, it was all over."

"The United Nations war objective is the unconditional surrender of the Axis Powers. The accomplishment of this objective may require the invasion of Japan." Thus stated the Joint Chiefs of Staff in a May 1943 memorandum on strategic plans for Japan. This is the earliest plant to mention the possibility of invasion. But as long as the Japanese islands remained a distant objective any discussion was academic. It was not until the 1944-1945 winter that Allied forces had reached positions which permitted a serious study of the question.

The 3 October 1944 JCS directive that provided for the Luzon, Iwo Jima, and Okinawa operations not only completed the strategic preparations for the invasion but settled the question of the route of approach to the Japanese islands. With both the success of Manhattan Project and Russian assistance in the final stages of the Pacific war uncertain, American planners had to assume that a difficult and bloody invasion would be necessary to bring Nippon to her knees. The assumption, however, was challenged by several Navy and Air Force leaders who felt that a naval and air blockade would force surrender.

When Japanese Imperial General Headquarters (IGHQ) had given up on Leyte, in December 1944, even Japanese sources admit that the over-all outcome of the Pacific war had been decided: There was no further hope of frustrating the Americans. Former Prime Minister Konoye told the Emperor privately in February 1945, "I think there is no longer any doubt about our defeat."

IGHQ anticipated that the Americans would now intensify their air and naval operations throughout the Pacific theater and would seek to neutralize the Japanese homeland. Japan Proper was in the process of being isolated from the Asian continent and from the Southwest Pacific region. Exhaustion of Japanese production resources and demoralization of the populace had been begun. The main Japanese naval, air, and ground forces were being sought out and destroyed (as at Leyte). Next the islands of Japan would be brought within the range of American land-based fighters. IGHQ also expected American operations designed to move forward the strike bases around Iwo Jima, Okinawa, Taiwan, central China, and perhaps south China, Hainan, and the Kuriles. If Japanese strength were sufficiently eroded after Iwo fell, the Americans might even attack Japan directly by mid-1945. Ordinarily, however, the enemy could be expected to consolidate positions in the Philippines and the Marianas, and to accelerate preparations to invade the Japanese homeland. This process ought to be completed by August or September 1945.

U.S. planner's work led to the JCS 25 May 1945 directive. It proposed to force Japan's unconditional surrender through a combination of lowering her ability and will to resist and the seizing of portions of the industrial heartland of Honshu. The directive set up a two step assault beginning 1 November 1945 to accomplish the second objective. Although considered only tentative when issued the plan was not appreciably altered in later discussions. Its final reconsideration came in a series of White House conferences during June. On the 18th, President Truman approved the plans although he requested a study of the cost in money and lives. But so complex was the study that it was never finished.

With the intensification of enemy pressure from all sides, strengthening of the homeland defenses had commanded Japanese attention, especially after the fall of Saipan. Yet the setup, according to a Japanese evaluation, was "deplorable;" greater progress was being made overseas. Much strength had had to be diverted to defend the Philippines. In Japan itself, things were not proceeding smoothly. Labor was lacking, and there were difficulties with mobilization and billeting, production, weapons, and food, regulations and procedures, jurisdiction and duties, etc. Countrywide war weariness was deepening.

The Allied operations envisioned would have ultimately involved 5,000,000 men and the largest concentrations of planes and ships yet used in a single operation. The bulk of the force would be American although the British Commonwealth would contribute three divisions of troops (one each from Britain, Canada, and Australia), the British Pacific Fleet, and a small number of air squadrons. The limited British contribution was largely a practical matter resulting from the logistical difficulties in supplying them with unique items. In part it also grew out of past difficulties in combined planning. Similar reasons led to a rejection of the contingents offered by France and the Netherlands.

The first phase of the invasion of the Japanese home islands was to be Operation OLYMPIC. This 400-mile jump from Okinawa to southern Honshu was scheduled for 1 November. It had three objectives: the isolation of the southern Japanese island, destruction of the Japanese forces there, and most important the seizure of site the airfields and bases needed to support the invasion of Honshu. The second phase, Operation CORONET, was to be a massive invasion of Honshu in March of 1946.

Overall responsibility for the invasion rested on General of the Army MacArthur who had named Commander-in-Chief, US Army Forces Pacific, in April as a preliminary. Fleet Admiral C. W. Nimitz had charge of the naval aspects of the campaign while retaining his two hats as Commander-in-Chief, Pacific Fleet and Pacific Ocean Areas.

MacArthur picked Gen. Krueger's veteran Sixth Army to stage the initial assault. That army, resting after the Luzon campaign, had formed the backbone of the advance northward from New Guinea. The nearly half a million troops would stream ashore from Admiral R. A. Spruance's Fifth Fleet. It was the first time that MacArthur's soldiers would land from the ships of that famous fleet which had executed nearly all the landings in the long westward advance across the Central Pacific. For the first time both Fifth and Third Fleets would operate simultaneously with Adm. W. F. Halsey's carrier groups supplying strategic cover and support.

In broad outlines the OLYMPIC Plan offered little new except for its size and complexity. It provided for a four corps landing on the east and west sides of the southern tip of Kyushu; the consolidation of the beachheads; and a drive northward to the Sendai-Tsuno line. There the OLYMPIC phase would end and succeeding operations be governed by later events. American strategy not necessarily look forward to the conquest of the entire island since the main objective of OLYMPIC was the acquisition of real estate-the ground on which to build the airfields and supply bases from which to support CORONET. Thus the most important objective would be the securing of Kagoshima Wan. That great landlocked bay had been picked by the planners as the port through which the men and supplies would flow for the post-invasion buildup. It would also serve as the Navy's advance base for CORONET.

The greatest danger to the assault was assumed to come from the air. The Americans expected opposition from 5,000 kamikazes, a realistic estimate in keeping with Japanese plans (KETSU-GO Operation). These called for 5,000 planes to be expended in attacks on the invasion force, whose appearance was expected sometime after September. The Japanese estimated that the assault force would be carried in 1,000 transports and that if half were sunk in the first ten days the landings could be smashed. Using the 1:6 ratio derived from their Okinawa experience, Japanese planners estimated this would require 3,000 planes. They assigned an additional 350 kamikazes to attacks on the carrier forces. The remaining 1,650 included those under repair and lost before the attack. As late as 15 July, however, only 70% of the required planes were in hand so it seems reasonable to assume that aerial opposition would have been less than expected.

Of great concern to the American planners were the 60 airfields on Kyushu and the five additional ones under construction. This would give great opportunities for dispersal and increased the difficulties of eliminating the suicide planes on the ground. Dispersal obviously complicated the air defense problems of the beachhead and the attack force, a job already made difficult by the close proximity of the main Japanese air bases. This was one of the reasons that the assault plan contained provisions for the seizure of offshore islands for radar and fighter control stations prior to the main landings.

Covering the Japanese home islands were four ground armies of eight ground divisions (one in Kyushu and five in the Kanto area), plus three brigades, four AAA divisions (with 1200 guns), and 14 cadre divisions. Nominally there were two air armies but the one centering on the Kanto district had an operational strength of only 50 planes, and the other (on Honshu) was only a training force. The three air defense divisions comprised less than 900 fighters. Coastal defenses were behind schedule, and secondary sectors were still in the planning stage. Weapons were poor, quality was deteriorating, ammunition was short, and training levels were low.

From the outset of 1945 the Japanese High command struggled to improve the defensive posture in the homeland where 2 1/2 million men were supposed to confront an invasion. It was hoped to transfer many troops and munitions home from the Asian continent by autumn, but this task grew more difficult with the acceleration of American assaults, and the consequent decrease in Japanese strength. In January 1945 the first joint Army-Navy operational plan was devised, stressing decisive combat in the homeland but the gaining of time through delaying operations on the periphery, especially Okinawa. Surprise and "special attacks" (a euphemism for suicide assaults) were to be the main points of Japanese strategy. The front line of the heartland perimeter would be southern Kuriles-Bonin-Ryukyus-Taiwan-Shanghai. Operational preparations against American landings would be accomplished in the regions of the Kanto, Kyushu, Eastern Sea (Tokai), and South Korea. Particular emphasis would be ascribed to air defense of these districts and the Osaka-Kobe (Hanshin) section. Every effort would be made to destroy the attackers while they were still in the water, in the main battle theater of the Pacific and the East China Sea.

Immense manpower levies were to be raised, on the basis of the new operational plans, within a few months: 56 divisions, 38 brigades, etc.-involving between 1,500,000 and 2,000,000 new men. Army headquarters were abolished and replaced by operational area army headquarters, and army district headquarters (mainly handling military administration). Munitions soon proved to be a serious problem. Stocks of light machine guns to outfit the new units amounted to only 23%; of small arms, only 50%. Materiel would have to he brought in from the Kwantung Army in Manchuria, or from the Navy, or else produced in 1945; but priority had to be given the production of 9,000 special-attack boats and 16,000 planes.

continued in part 2

Question? Comment? Newsletter? Send me an email. Blue skies! -- Dan Ford

Question? Comment? Newsletter? Send me an email. Blue skies! -- Dan Ford