Chapter I:
Operation Iceberg
On 3 October 1944 American forces in the Pacific Ocean Areas received a directive to seize positions in the Ryukyu Islands (Nansei Shoto). Okinawa is the most important island of the Ryukyu Group, the threshold of the four main islands of Japan. The decision to invade the Ryukyus signalized the readiness of the United States to penetrate the inner ring of Japanese defenses. For the enemy, failure on Okinawa meant that he must prepare to resist an early invasion of the homeland or surrender.
The Strategic Decision
Operation ICEBERG, as the plan for the Okinawa campaign was officially called, marked the entrance of the United States upon an advanced stage in the long execution of its strategy in the Pacific. Some 4,000 miles of ocean, and more than three years of war, separated Okinawa from Pearl Harbor. In 1942 and 1943 the Americans had contained the enemy and thrown him back; in 1944 their attack gathered momentum, and a series of fierce island campaigns carried them toward the Japanese inner stronghold in great strides.
The Allied advance followed two main axes, one through the islands of the Central Pacific, the other through the South and Southwest Pacific. Navy task forces and some other elements operated on both fronts as needed. The result was "unremitting pressure" against Japanese military and naval might, a major objective of American strategy.
Near the close of 1943, a thrust at the Gilbert Islands from the Central Pacific, in which Tarawa, Makin, and Apamama were seized, paved the way for the assault on the Marshalls on 31 January 1944. American forces captured Kwajalein, Majuro, and Eniwetok, and their fleet and air arms moved forward. At the same time, American carriers heavily attacked Truk, and that formidable enemy naval base in the Carolines was thenceforth immobilized. Saipan, Tinian, and Guam in the Marianas fell to American arms in the summer of 1944, and, in the First Battle of the Philippine Sea, the U. S. Navy administered a crushing defeat to the Japanese fleet that tried to interfere with the American push westward. In September and October the Americans occupied Ulithi in the western Carolines for use as an anchorage and advanced fleet base, and took Angaur and Peleliu in the Palau Islands, situated close to the Philippines.
Meanwhile, American forces in the South and Southwest Pacific were approaching Mindanao, southernmost of the Philippine Islands, by advances through the Solomons and New Guinea in which Japanese armies were neutralized and isolated on Bougainville, New Ireland, and New Britain. The capture of Wakde on the northeastern coast of New Guinea in May 1944 was followed by the seizure of Biak and Noemfoor. During the summer a Japanese army attempting to break out from Wewak in Australian New Guinea was subdued. The invasion of Morotai in September placed American forces within 300 miles of Mindanao.1 (See Map No. I.)
The ultimate goal of American operations in the Pacific was the industrial heart of Japan, along the southern shores of Honshu between the Tokyo plain and Shimonoseki. American strategy aimed to reach this objective by successive steps and to take advantage, on the way, of Japan's extreme vulnerability to submarine blockade and air bombardment. Throughout most of 1944 Army and Navy staffs in the Pacific Ocean Areas had been planning for the invasion of Formosa (Operation CAUSEWAY) in the spring of 1945. On the basis of the Joint Chiefs of Staff directive of March 1944, the general concept of this operation had been outlined, the availability of troops considered and reviewed many times, and the assignment of task force commanders announced. On 23 August, a joint staff study for CAUSEWAY had been published. It was clear that Admiral Chester W. Nimitz, Commander in Chief, U. S. Pacific Fleet and Pacific Ocean Areas, intended to invade Formosa after Southwest Pacific forces had established positions in the Central and Southern Philippines; CAUSEWAY, in turn, was to be followed by operations against the Ryukyus and Bonins, or against the China coast. Either course would lead eventually to assault on the Japanese home islands.2
On 15 September the Joint Chiefs directed Gen. Douglas MacArthur to seize Leyte on 20 October, instead of 20 December as planned, and to bypass Mindanao. At the same time, Admiral Nimitz was instructed to bypass Yap 3 On the next day Admiral Nimitz reconsidered the Formosa operation. He believed that the early advance into the Central Philippines, with the opportunity of acquiring the desired fleet anchorages there, opened up the possibility of a direct advance northward through the Ryukyus and Bonins rather than through Formosa and the China coast. He reviewed the objectives of CAUSEWAY the establishment of air bases from which to bomb Japan, support China, and cut off the home islands from resources to the south- with reference to the new possibility and in a letter to his Army commanders requested their opinions on the subject.4
Lt. Gen. Robert C. Richardson, Jr., Commanding General, U. S. Army Forces, Pacific Ocean Areas, replied that only those steps should be taken which would lead to the early accomplishment of the ultimate objective-the invasion of Japan proper. From this point of view the occupation of Formosa as a stepping stone to an advance on Japan via the China coast did not, in his opinion, offer advantages commensurate with the time and enormous effort involved. He proposed instead, as a more economical course, a dual advance along the LuzonRyukyus and the Marianas-Bonins axes. He fully agreed with General MacArthur's plan to seize Luzon after Leyte. The seizure of Luzon would provide air and naval bases in the Philippines from which enemy shipping lanes in the China Sea could be blocked and, at the same time, Formosa effectively neutralized. From the ample bases in Luzon, it would be possible and desirable to seize positions in the Ryukyus for the prosecution of air operations against Kyushu and Honshu. The occupation of bases in the Bonins would open another route from the Marianas for bomber operations against Japan. The air assaults on Japan would culminate in landings on the enemy's home islands 5
Lt. Gen. Millard F. Harmon, Commanding General, U. S. Army Air Forces, Pacific Ocean Areas, in his reply to Admiral Nimitz referred to a previous letter which he had written to the Admiral, recommending, as an alternative to the invasion of Formosa and the China coast, the seizure of islands in the Ryukyu chain, for development as air bases from which to bomb Japan. He restated these views and emphasized his opinion that if the objective of CAUSEWAY was the acquisition of air bases it could be achieved with the least cost in men and materiel by the capture of positions in the Ryukyus.6
The commander of the ground troops designated for CAUSEWAY, Lt. Gen. Simon B. Buckner, Jr., Commanding General, Tenth Army, presented the primary objection to the entire Formosa operation. He informed Admiral Nimitz that the shortages of supporting and service troops in the Pacific Ocean Areas made CAUSEWAY unfeasible. General Buckner added, about a week later, that if an invasion of Luzon was planned the need for occupying Formosa was greatly diminished. 7
Admiral Nimitz communicated the substance of these views to Admiral Ernest J. King, Commander in Chief, U. S. Fleet. The latter, who had been the chief proponent of an invasion of Formosa, proposed to the Joint Chiefs of Staff on 20ctober 1944 that, in view of the lack of sufficient resources in the Pacific Ocean Areas for the execution of CAUSEWAY and the War Department's inability to make additional resources available before the end of the war in Europe, operations against Luzon, Iwo Jima, and the Ryukyus be undertaken successively, prior to the seizure of Formosa. Favorable developments in the Pacific and in Europe might make CAUSEWAY feasible at a later date.8 On the next day, 3 October, the Joint Chiefs of Staff issued a directive to Admiral Nimitz to seize one or more positions in the Ryukyu Islands by 1 March 1945.9 On 5 October Admiral Nimitz informed his command that the Formosa operation was now deferred and that, after General MacArthur invaded Luzon on 20 December 1944, the Pacific Ocean Areas forces would seize Iwo Jima on 20 January 1945 and positions in the Ryukyus on 1 March. 10
The projected Ryukyus campaign was bound up strategically with the operations against Luzon and Iwo Jima; they were all calculated to maintain unremitting pressure against Japan and to effect the attrition of its military forces. The Luzon operation in December would allow the Southwest Pacific forces to continue on the offensive after taking Leyte. The occupation of Iwo Jima in January would follow through with another blow and provide a base for fighter support for the B-29's operating against Japan from the Marianas. The seizure of Okinawa in March would carry the war to the threshold of Japan, cut the enemy's air communications through the Ryukyus, and flank his sea communications to the south. Okinawa was, moreover, in the line of advance both to the China coast and to the Japanese home islands.11
MAP NO. 1: Ryukyu Islands
MAP NO. 1
MAP NO. 2: Okinawa Island Group
MAP NO. 2
The direct advance to the Ryukyus-Bonins line from the Luzon-Marianas was thus conceived within the framework of the general strategy of destroying by blockade and bombardment the Japanese military forces or their will to resist. The Ryukyus were within medium bomber range of Japan, and it was estimated that 780 bombers, together with the necessary number of fighters, could be based there. An advanced fleet anchorage was available in Okinawa. From these airfields and naval bases American air and naval forces could attack the main islands of Japan and, by intensified sea and air blockade, sever them from the Japanese conquests to the south. The captured bases could also be used to support further operations in the regions bordering on the East China Sea. Finally, the conquest of the Ryukyus would provide adequate supporting positions for the invasion of Kyushu and, subsequently, Honshu, the industrial heart of Japan. 12
Nature of the Target
The Islands
The Ryukyu Islands lie southwest of Japan proper, northeast of Formosa and the Philippines, and west of the Bonins. (See Map No. l.) The islands, peaks of submerged mountains, stretch in an arc about 790 miles long between Kyushu and Formosa and form a boundary between the East China Sea and the Pacific Ocean. The archipelago consists of about zoo islands, only 30 of which are large enough to support substantial populations. The climate is subtropical, the temperature ranging from about 60° F. to 83° F. Rainfall is heavy, and the high humidity makes the summer heat oppressive. The prevailing winds are monsoonal in character, and between May and November each year the islands are visited by destructive typhoons.13
Approximately in the center of the arc is the Okinawa Group (Gunto) of some fifty islands clustered around the island of Okinawa. The Kerama Islands lie in an area from ten to twenty miles west of southern Okinawa. Kume, Tonachi, Aguni, and Tori form a rectangle to the north of the Kerama Group. Ie Shima stands off the jutting tip of the Motobu Peninsula on northern Okinawa, while farther to the north lie the Iheya Islands and Yoron. A chain of small islands, called by the Americans the Eastern Islands, extends along the eastern shore of southern Okinawa. Lying in the path of the Japan Current, the entire Okinawa Group is surrounded by seas warm enough to allow the growth of coral, and hence all the islands are surrounded by fairly extensive reefs, some of which extend several miles off shore. (See Map No. 2.)
Okinawa is the largest of the islands in the Ryukyus. Running generally north and south, it is 60 miles long and from a to 18 miles wide, with an area of 485 square miles. It is entirely fringed with reefs: on the western side the reef lies fairly close to shore and is seldom over a mile wide; on the eastern side, where the coast is more sheltered, the reef extends for some distance off shore, the widest and shallowest points being north of Nakagusuku Bay. (See Maps Nos.II and III.)
Photo: OKINAWAN CUSTOMS
OKINAWAN CUSTOMS include the burial tomb and the veneration of ancestors. The
burial tombs characteristics of the Okinawan landscape stand out clearly in this aerial view
(above) just north of Shuri.
Photo: OKINAWANS
OKINAWANS, their head man, and a native priest (white hat) gather around an American
soldier-interpreter as he ask questions
When Commodore Perry's ships sailed into Naha Harbor, on 26 May 1853, Okinawa was a semi independent country, paying tribute to China and Satsuma. It was annexed in 1879 by Japan, which integrated the Okinawan people almost completely into the Japanese governmental, economic, and cultural structure. The racial origins of the Okinawans are similar to, but not identical with, those of the Japanese, and the Okinawan stock and culture had been subject to extensive Chinese influence. While the Okinawans generally resemble the Japanese in physique, they differ appreciably in their language, the native Luchuan tongue. The predominant religion among the Okinawans is an indigenous, animistic cult, of which worship of fire and the hearth is typical; veneration of ancestors is an important element in this religion and the burial tomb the most characteristic feature of the Okinawa landscape a feature which the Japanese were to convert into a formidable defensive position.
The standard of living of the Okinawan people is low; the Japanese made no attempt to raise it, regarding the Okinawans as inferior rustics. Most of the inhabitants subsist on small-scale agriculture. When the invading Americans climbed up from the beaches, they found every foot of usable land cut into small fields and planted with sugar cane, sweet potatoes, rice, and soy beans. In 1940 the population of the island was 435,000.
The terrain in northern Okinawa, the two-thirds of the island above the Ishikawa Isthmus, is extremely rugged and mountainous. A central ridge, with elevations of 1,000 feet or more, runs through the length of the region; the ridge is bordered on the east and west by terraces which are dissected by ravines and watercourses, and it ends at the coast in steep cliffs. About 80 percent of the area is covered by pine forests interspersed with dense undergrowth. Troop movements are difficult in the region as the use of vehicles is confined to the poor road that hugs the western shore. The Motobu Peninsula, which is nearly square in shape and juts to the west, has also a mountainous and difficult terrain. Two mountain tracts separated by a central valley run east and west the length of the peninsula. Successive coastal terraces are well developed on the north, east, and west of the peninsula. About three and one-half miles off the northwest end of the Motobu Peninsula is the small flat-topped island of Ie Shima, with a sharp pinnacle about 500 feet high at the eastern end. The southern third of Okinawa, south of Ishikawa, is rolling, hilly country, lower than the north but broken by terraces, steep natural escarpments, and ravines. This section is almost entirely under cultivation and contains threefourths of the population of the island; here, too, are the airfields and the large towns-Naha, Shuri, Itoman, and Yonabaru. It was in this area that the battle for Okinawa was mainly fought. The limestone plateau and ridges are ideal for defense and abound in natural caves and burial tombs, easily developed into strong underground positions. Generally aligned east and west, the hills offer no north-south ridge line for troop movement, and thus they provide successive natural lines of defense, with frequent steep slopes created by artificial terracing. Rice paddies fill the lowlands near the coasts. The roads are more numerous than in the north, but, with the exception of those in Naha and its vicinity, they are mostly country lanes unsuited for motorized traffic. Drainage is generally poor, and heavy rains turn the area into a quagmire of deep, clay-like mud.
South of Zampa Point on the west there is a 15,000-yard stretch of coast line which includes nearly 9,000 yards of beaches, divided by the Bishi River. These are known as the Hagushi beaches, deriving their name from a small village at the mouth of the river. The beaches are not continuous but are separated by cliffs and outcropping headlands. They range from 100 to 900 yards in length and from 20 to 45 yards in width at low tide, and some are completely awash at high water. A shallow reef with scattered coral heads borders the entire stretch of beach and, in many places, is almost a barrier reef, with deeper water between its crest and the shore line than immediately to seaward. The beaches are for the most part coral sand and most have at least one road exit. A low coastal plain flanks the beaches from Zampa Point south to Sunabe; it is dominated by rolling hills which afford excellent observation, good fields of fire along the beaches, and extensive cover and concealment. Less than 2,000 yards inland on the plain lie the Yontan and Kadena airfields, north and south of the Bishi River. A 400foot-high hill mass, rising southeast of Sunabe and extending across the center of the island, dominates the entire beachhead area. Composed of innumerable sharp ridges and deep ravines, it is a major obstacle to rapid troop movements and can be used effectively for a strong delaying action.
South of the Sunabe hills, down to the Uchitomari-Tsuwa line, the island narrows to 5,500 yards. The terrain is essentially similar to that behind the Hagushi beaches, with heavily wooded uplands and extensively terraced and cultivated valleys and lower slopes. The hills and ridges are generally low except for some high peaks in the general vicinity of Kuba on the east coast, from which observation of the area is excellent. Roads are adequate for light Japanese transport but not for the heavy strain of American military traffic.
Photo: OKINAWA'S LANDSCAPE
OKINAWA'S LANDSCAPE in the south is marked by fields of grain and vegetables,
broken only by humps of coral, farmhouses, and villages. Navy plane flying over such
terrain is shown dropping supplies to the last fast-moving American troops early in the campaign
Photo: VILLAGES ON OKINAWA
VILLAGES ON OKINAWA consist of small clusters of houses surrounded by vegetation-
covered stone and mud walls. Note camouflaged Japanese Army trucks
On the east coast, the Katchin Peninsula on the north and the Chinen Peninsula on the south extend into the ocean to inclose the spacious fleet anchorage of Nakagusuku Bay, called by the American troops "Buckner" Bay. A low coastal plain from one-fourth to one mile wide runs along the shore of the bay from the Katchin Peninsula to Yonabaru. At Yonabaru the plain extends inland to the west through an area of moderate relief and joins another coastal flat extending northeastward from Naha. A cross-island road follows this corridor and connects the two cities. Naha, the capital of the island, with a population of 65,000, is Okinawa's chief port and can accommodate vessels up to 3,000 tons. Southwest of the city, on the Oroku Peninsula, was the Naha airfield, the most highly developed field on the island.
In the region north of the Naha-Yonabaru corridor and in the vicinity of Shuri, the ancient capital of Okinawa, lies the most rugged terrain in the southern part of the island. From the high ground near Shuri and from many other vantage points in this area observation is excellent to the north and south and over the coastal regions. At the highest point the hills rise about 575 feet, but the lack of pattern, the escarpments, steep slopes, and narrow valleys characteristic of the region make the major hill masses ideal territory for defense. Many of the escarpments are sheer cliffs without topsoil or vegetation. The low ground is filled with twisting ridges and spotted with small irregular knolls, rendering observation difficult and providing excellent locations for minor infantry and antitank positions. The most prominent features of the region are the strong natural defensive line of the Urasoe-Mura Escarpment, rising from the west coast above the Machinato airfield and running for 4,500 yards across the island in a southeasterly direction, and the chain of hills through Tanabaru and MinamiUebaru to the east coast southwest of Tsuwa.
South of the strong Shuri positions the terrain is rough, but there are few large escarpments. There are some broad valleys and an extensive road net which would facilitate troop movements. The terrain in the southern end of the island consists of an extensive limestone plateau, surrounded by precipitous limestone cliffs. The northern side of the plateau is a 300-foot escarpment which rises vertically from the valley floor in a jagged coral mass. On the top of the plateau major hills-Yuza-Dake and Yaeju-Dake-cover all approaches from the north, east, and west. Along the southeastern coast, much of the stretch from Minatoga to the eastern end of the Chinen Peninsula consists of beaches. These are dominated by the rolling dissected terrace forming the body of the peninsula and by the high plateau to the southwest.
American Intelligence of the Enemy
American knowledge of the enemy and of the island of Okinawa was acquired slowly over a period of many months and in the face of many difficulties. With Okinawa isolated from the world by the Japanese, information of military value concerning this strategic inner defense line of the Empire was scarce and difficult to obtain. Limited basic intelligence was garnered from documents and prisoners captured on Pacific island battlefields, from interrogation of former residents of the Ryukyus, and from old Japanese publications. The great bulk of the data was obtained through aerial photographic reconnaissance. This, however, was often incomplete and inadequate, particularly for terrain study and for estimating enemy strength and activity. The distance of the target from American air bases-1,200 nautical miles-necessitated the use of B-29's and carrier planes for photographic missions; the former afforded only high-altitude, small-scale coverage, while the latter depended on the scheduling of carries strikes. The relatively large land masses involved and the prevalence of cloud cover added to the difficulty of obtaining the large-scale photographs necessary for detailed study of terrain and installations.14
The target map prepared by American intelligence represented all that was known of the terrain and the developed facilities of the island. This map, scale 1 : 25,000, was based on aerial photographs obtained on 29 September and 10 October 1944 and was distributed about 1 March 1945. Incomplete coverage, varying altitudes of the planes, and cloudiness over parts of the island at the time prevented clear delineation, and certain portions of the map, including that of the high ground north of Shuri, had either poor topographic detail or none at all. Additional photographic coverage of the island was obtained on 3 and 22 January, 28 February, and 1 March 1945; that of 22 January was excellent for the proposed landing beach areas. To supplement aerial photography a submarine was sent from Pearl Harbor to take pictures of all Okinawa beaches. The submarine never returned.15
Hydrographic information was complete, but its accuracy could not be checked until the target was reached. As the data agreed with a captured Japanese map they were presumed to be accurate. The most reliable information on the depth of the water over the reefs was obtained from Sonne Strip photography and was made available to the troops in March.16
The first estimate of enemy strength, made in October 1944, put the number of Japanese troops on Okinawa at 48,600, including two infantry divisions and one tank regiment.17 In January 1945 this estimate was raised to 55,000, with the expectation that the Japanese would reinforce the Okinawa garrison to 66,000 by 1 April 1945. At the end of February, however, the January estimate was still entertained. All these figures were based on interpretation of aerial photographs and on the use of standard Japanese Tables of Organization: there was no documentary evidence corroborating the estimate of the number of troops on the island. 18
It was believed that the Japanese had moved four infantry divisions to the Ryukyus during 1944. These were identified as the 9th, 62d, 24th, and 28th Divisions. Army intelligence learned that one division, perhaps the 9th, had been moved from Okinawa to Formosa in December 1944. In March 1945 American intelligence estimated that the Japanese forces on Okinawa consisted of the following troops, which included 26 battalions of infantry.
Headquarters 32d Army 625
24th Division (triangular) 15,000-17,000
62d Division (square) 11,500
44th Independent Mixed Brigade 6,000
One independent mixed regiment 2,500
One tank regiment 750
One medium artillery regiment, two mortar battalions, one anti-tank battalion, three antitank companies, and antiaircraft units 5,875
Air-ground personnel 3,500
Service and construction troops 5,000-6,000
Naval-ground troops 3,000
Total 53,000-56,000
It was considered possible that elements of the 9th and 28th Divisions might also be present on Okinawa proper. Enemy forces were known to be organized under the 32d Army, commanded, it was thought, by General Watanabe, with headquarters at Naha. Shortly before the landings the estimate of Japanese troops was raised to 65,000 on the basis of long-range search-plane reports of convoy movements into Naha.19
Calculations based on Japanese Tables of Organization indicated that the enemy could be expected to have 198 pieces of artillery Of 70-mm. or larger caliber, including twenty-four 150-mm. howitzers.20 The Japanese were presumed to have also about 100 antitank guns of 37-mm. and 47-mm. caliber in addition to the guns carried on tanks. The tank regiment on Okinawa had, according to Japanese Tables of Organization, 37 light and 47 medium tanks, but one estimate in March placed the total number of tanks at 90. Intelligence also indicated that rockets and mortars up to 250 mm. could be expected.21
Aerial photographs disclosed three main defense areas on Okinawa, centering in Naha, the Hagushi beaches, and the Yonabaru-Nakagusuku Bay area on the east coast. Prepared positions for four infantry regiments were noted along the bay; for one regiment, behind the Hagushi beaches; and for one battalion, along the beaches at Machinato above Naha. It was believed that a total of five or six battalions of troops would be found in the northern part of Okinawa and le Shima and that two divisions would be concentrated in southern Okinawa. The main strength of the Japanese artillery was believed to be concentrated in two groups-one about two miles east of Yontan airfield and the other about three miles due south of Shuri; the probable presence of guns was deduced from the spoil which had been deposited in front of cave or tunnel entrances on the slopes of ridges in a manner suitable for gun emplacements.22
At the end of March 1945 intelligence indicated that there were four operational airfields on Okinawa at Naha, Yontan, Kadena, and Machinato; the first two were the best. All were heavily defended with numerous antiaircraft and dual purpose gun emplacements. The Yonabaru strip, which had been in an initial stage of construction in October 1944, was reported as having been abandoned by February 1945. Apparently not intending to defend Ie Shima very determinedly, the Japanese, in the latter part of March, were reported to have rendered the airfield there unusable by digging trenches across the runways.23 Land-based enemy aircraft on Okinawa was not expected to constitute a danger; the Americans fully expected that the airfields would be neutralized by the time they invaded the island. It was reported on 29 March, however, that enemy fighter and transport planes were being flown in at night to the Kadena airfield. On 31 March no activity was observed on any of the Okinawa airfields. It was constantly stressed that heavy enemy air attacks would probably be launched from Kyushu, 350 miles to the north. The potential threat of small suicide boats against shipping was also pointed out. 24
Tenth Army believed that the most critical terrain for the operation was the area between the Ishikawa Isthmus and the Chatan-Toguchi line, particularly the high ground inland which dominates the Hagushi beaches and the valley of the Bishi River. The enemy could defend the beaches from prepared positions with one regiment, maintaining mobile reserves in the hills north and south of the river. Other reserves could be dispatched to the landing area within a few hours. It was expected that the Japanese would wait until the night of L Day to move their artillery. Alerted by American preliminary operations, they might have a division in position ready for a counterattack on the morning of the landings. From terrain 3,000 yards inland that offered both cover and concealment, the Japanese could launch counterattacks of division strength against both flanks of the landing area simultaneously. If the landings were successful, the enemy's main line of resistance, manned by a force of from nine to fifteen battalions, was expected to be at the narrow waist of the island, from Chatan to Toguchi, south of the landing beaches. 25
The Plan of Attack
The plan for the conquest of the Ryukyus was in many respects the culmination of the experience of all previous operations in the Pacific war. It embodied the lessons learned in the long course of battle against the Japanese outposts in the Pacific-lessons of cooperation and combined striking power of the services, of the technique of amphibious operations, and of Japanese tactics and methods of meeting them. The plan for ICEBERG brought together an aggregate of military power-men, guns, ships, and planes that had accumulated during more than three years of total war. The plan called for joint operations against the inner bastion of the Japanese Empire by the greatest concentration of land, sea, and air forces ever used in the Pacific.
Photo: AMERICAN COMMANDERS
AMERICAN COMMANDERS in Operation ICEBERG: Admiral Raymond A. Spruance,
Fleet Admiral Chester W. Nimitz, and Lt. Gen. Simon B. Buckner.
Basic Features of the Plan
The immediate task imposed upon the American forces by the terms of the general mission was the seizure and development of Okinawa and the establishment of control of the sea and air in the Ryukyus. The campaign was divided into three phases. The seizure of southern Okinawa, including Keise Shima and islands in the Kerama Group, and the initiation of the development of base facilities were to constitute the first phase. In the next phase Ie Shima was to be occupied and control was to be established over northern Okinawa. The third phase consisted of the seizure and development of additional islands in the Nansei Shoto for use in future operations. The target date of the operation was set at 1 March 1945. 26
Planning began in October 1944. The general scheme for Operation ICEBERG was issued in the fall of 1944 by Admiral Nimitz as Commander in Chief, Pacific Ocean Areas (CINCPOA). The strategic plan outlined was based on three assumptions. First, the projected campaign against Iwo Jima would have progressed to such an extent that naval fire-support and close air-support units would be available for the assault on Okinawa. Second, the necessary ground and naval combat units and assault shipping engaged in the Philippines would be released promptly by General MacArthur for the Okinawa campaign. Third, preliminary air and naval operations against the enemy would ensure control of the air in the area of the target during the operation.27
Air superiority was the most important factor in the general concept of the operation as outlined by Admiral Nimitz's staff. The CINCPOA planners believed that American air attacks on Japan, from carriers and from airfields in the Marianas, combined with the seizure of Iwo Jima, would force a concentration of enemy air strength around the heart of the Empire-on the home islands, Formosa, the China coast, and the Ryukyus. From these bases, strong and continuous air attacks would be made against the forces invading the Ryukyus. It would be necessary, therefore, to neutralize or destroy enemy air installations not only at the target but also at the staging areas in Kyushu and Formosa. All available carrier- and land-based air forces would be called on to perform this task and give the Americans the control of the air required in the area of operations. On Okinawa itself, the scheme of maneuver of the ground troops would be such as to gain early use of airfields that would enable landbased planes to maintain control of the air in the target area. Control of the sea was to be maintained by submarine, surface, and air attacks on enemy naval forces and shipping. 28
CHART I
Organization of Allied Forces for the Ryukyus Campaign,
January 1945
CHART 1: Organization of Allied Forces for the Ryukyus Campaign
Source: Commander in Chief, U.S. Pacific Fleet and Pacific Ocean Areas, Operations in the
Pacific Ocean Areas, April 1945, Plate I, opp. p. 76 (with adaptations).
The American Forces
The isolation of Okinawa was to be effected with the aid of land-based air forces of commands outside the Pacific Ocean Areas (POA). Planes from the Southwest Pacific Area (SWPA) were to engage in searches and continuous strikes against Formosa as soon as the situation on Luzon permitted. Twentieth Air Force B-29's from China and the Marianas were to bomb Formosa, Kyushu, and Okinawa during the month preceding the landings. The China-based XX Bomber Command was to concentrate on Formosa, while the XXI Bomber Command from the Marianas would attack Okinawa and then shift to Kyushu and other vulnerable points in the home islands during the fighting on Okinawa. The Fourteenth Air Force was to conduct searches along the China coast and also, if practicable, bomb Hong Kong.29
All the forces in Admiral Nimitz's command were marshaled in support of the ICEBERG Operation. (See Chart 1.) The Strategic Air Forces, POA, was assigned the task of neutralizing enemy air bases in the Carolines and the Bonins, of striking Okinawa and Japan when practicable, and of providing fighter cover for Twentieth Air Force bombing missions against Japan. The Commander, Forward Areas Central Pacific, was to use his naval air strength to provide antisubmarine coverage, neutralize bypassed enemy bases, and, in general, furnish logistic support. Provision of intelligence on enemy naval units and interdiction of the sea approaches from Japan and Formosa were the tasks of the Submarine Force, Pacific Fleet. The enemy was to be contained in the North Pacific Area, and the lines of communication were to be secured in the Marshalls-Gilberts area. Logistic support was to be provided by General Richardson's United States Army Forces, POA (USAFPOA), the Air and Service Forces, Pacific Fleet, and the South Pacific Force. All the armed forces in the Pacific Ocean Areas, from the West Coast to Ulithi and from New Zealand to the Aleutians, were directed to support the attack on Okinawa.30
CHART II
Organizations of Central Pacific Task Forces for the Ryukyus Campaign,
January 1945
CHART II: Organizations of Central Pacific Task Forces for the Ryukyus Campaign
Source: Commander in Chief, U.S. Pacific Fleet and Pacific Ocean Areas, Operations in the
Pacific Ocean Areas, April 1945, Plates I and II, opp. p. 76 (with adaptations).
The principal mission in seizing the objective was assigned to a huge joint Army-Navy task force, known as the Central Pacific Task Forces and commanded by Admiral Raymond A. Spruance, Commander of the Fifth Fleet. (See Chart II.) Admiral Spruance's forces consisted of naval covering forces and special groups (Task Force 50), which he personally commanded, and a joint Expeditionary Force (Task Force 51), commanded by Vice Admiral Richmond K. Turner, Commander, Amphibious Forces Pacific Fleet. General Buckner, Commanding General, Tenth Army, was to lead the Expeditionary Troops (Task Force 56) under Admiral Turner's direction.31
Command relationships prescribed for the operation differed in some respects from those in previous operations against island positions remote from Japan. Because the campaign would entail prolonged ground combat activities by a field army on a large island close to the enemy's homeland, it was necessary to define clearly the relationships between Army and Navy commanders for the successive phases of the operation. Admiral Nimitz accordingly provided that initially the chain of command for amphibious operations would be Admiral Spruance, Admiral Turner, General Buckner. However, when Admiral Spruance determined that the amphibious phases of the operation had been successfully completed, General Buckner was to assume command of all forces ashore. He was thereafter to be directly responsible to Admiral Spruance for the defense and development of the captured positions. In time, Admiral Spruance would be relieved by Admiral Nimitz of these responsibilities, and General Buckner would take over complete command of the forces in the Ryukyus. As Commander, Ryukyus Force, a joint task force of ground, air, and naval garrison troops, he would be responsible only to CINCPOA for the defense and development of the newly won bases and for the protection of the sea areas within twenty-five miles.32
Admiral Spruance, as commander of Task Force 50, had at his disposal Vice Admiral Mitscher's Fast Carrier Force (Task Force 58), a British Carrier Force (Task Force 57), special task groups for aerial search and reconnaissance and antisubmarine warfare, and fleet logistic groups. Task Force 58 had a major share of the mission of neutralizing Japanese air strength. Its fast carriers were to strike Kyushu, Okinawa, and adjacent islands in the middle of March, to remain in a covering position east of the target area during the week preceding the invasion, to support the landings with strikes and patrols, and to be prepared for further forays against Kyushu, the China coast, or threatening enemy surface forces. The British carriers, the first to participate in Pacific naval actions with the American fleet, were given the task of neutralizing air installations on the Sakishima Group, southwest of the Ryukyus, during the ten days before the landings. 33
CHART III
Organization of Expeditionary Troops for the Ryukyus Campaign,
January 1945
CHART III: Organization of Expeditionary Troops for the Ryukyus Campaign
Source: Commander Task Force 51, Commander Amphibious Forces, U. S. Pacific Fleet, Report on Okinawa Gunto Operations from February 17 May to 17 May 1945, Part 1, pp. 2-4; Tenth Army Action Report Ryukyus, 26 March to 30 June 1945, Ch. 2; Commander in Chief, U.S. Pacific Fleet and Pacific Ocean Areas, Operation in the pacific Ocean Areas, April 1945.
The Joint Expeditionary Force (Task Force 51) was directly charged with the capture and development of Okinawa and other islands in the group. It was a joint task force of Army, Navy, and Marine units and consisted of the Expeditionary Troops (Task Force 56-see Chart III), shipping to transport them, and supporting naval and air units. Direct naval and air support for Task Force 51 was to be furnished by its Amphibious Support Force (Task Force 52), made up of escort carriers, gunboat and mortar flotillas, mine sweepers, and underwater demolition teams, and by the Gunfire and Covering Force (Task Force 54) of old battleships, light and heavy cruisers, destroyers, and destroyer escorts. The transports and tractor units of the Northern Attack Force (Task Force 53) and Southern Attack Force (Task Force 55) were to land the ground troops in the main assault on the Okinawa beaches, while a number of task groups were assigned the task of transporting the troops for subsidiary landings and the floating and area reserves. Task Force 51 also included a transport screen, a service and salvage group, and several specialized naval units. 34
The troops who would assault the objectives constituted a field army, the Tenth Army, which had been activated in the United States in June 1944 and shortly thereafter had opened headquarters on Oahu. General Buckner formally assumed command in September 1944, having come to the new assignment from the command of the Alaskan Department, where for four years he had been organizing the American defenses in that area. His new staff included many officers who had served with him in Alaska as well as some from the European Theater of Operations. The major components of Tenth Army were XXIV Army Corps and III Amphibious Corps (Marine). The former consisted of the 7th and 96th Infantry Divisions and was commanded by Maj. Gen. John R. Hodge, a veteran leader of troops who had met and defeated the Japanese on Guadalcanal, New Georgia, Bougainville, and Leyte. III Amphibious Corps included the 1st and 6th Marine Divisions and was headed by Maj. Gen. Roy S. Geiger, who had successfully directed Marine operations on Bougainville and Guam. Three divisions, the 27th and 77th Infantry Divisions and the 2d Marine Division, were under the direct control of Tenth Army for use in special operations and as reserves. The area reserve, the 81st Infantry Division, was under the control of CINCPOA. Also assigned to Tenth Army for the purpose of defense and development of the objectives were a naval task group, the Tactical Air Force, and the Island Command. 35
A total of 183,000 troops was made available for the assault phases of the operation.36 About 154,000 of these were in the seven combat divisions, excluding the 81st Division, which remained in New Caledonia; all seven divisions were heavily reinforced with tank battalions, amphibian truck and tractor battalions, joint assault signal companies, and many attached service units. The five divisions committed to the initial landings totaled about 116,000. The 1st and 6th Marine Divisions, with 26,274 and 24,356 troops, respectively, each carried an attached naval construction battalion and about 2,500 replacements in addition to their other supporting combat and service units. The reinforced 7th, 77th, and 96th Divisions averaged nearly 22,000 men per division but each was about 1,000 understrength in organic infantry personnel. The 27th, a reserve division, was reinforced to a strength of 16,143 but remained nevertheless almost 2,000 understrength organically. The 2d Marine Division, also in Army reserve, numbered 22,195.37 (See Appendix C, Table No. 4)
Tenth Army, as such, had never directed any campaigns, but its corps and divisions had all been combat-tested before the invasion of the Ryukyus. XXIV Corps had carried out the conquest of Leyte, and III Amphibious Corps had captured Guam and Peleliu. The 7th Division had seen action on Attu, Kwajalein, and Leyte, the 77th on Guam and Leyte, and the 96th on Leyte. The 27th had taken part in the battles for the Gilberts and Marshalls and for Saipan. The 1st Marine Division had been one of the first to see action in the Pacific, on Guadalcanal, and had gone through the campaigns of Western New Britain and Peleliu. The 6th Marine Division had been activated late in 1944, but its regiments were largely made up of seasoned units that had fought on Guam, the Marshalls, and Saipan. The ad Marine Division had participated in the fighting on Guadalcanal, Tarawa, Saipan, and Tinian.
Plan for the Capture of Okinawa
Using the CINCPOA Toint Staff Study as a basis, each of the major commanders prepared his plans and issued his operation orders. Although each plan and operation order was derived from that of the next superior echelon, planning was always concurrent. The joint nature of the operation also required extensive coordination of the three services in all operational and logistical problems. Joint conferences thrashed out problems of troop lists, shipping, supplies, and strategy. Corps and task force commanders worked together on the plans for amphibious operations. Corps and division staffs were consulted and advised by Army for purposes of orientation and planning. To ensure inter-service coordination, Navy and Marine officers were assigned to work with Tenth Army general and special staff sections.38 In some cases planning was facilitated by utilizing the results of work on other operations. Thus the naval staff developing the gunfire support plans was able to use the operations at Iwo Jima to test and strengthen the general command and communications framework, which was generally similar for both operations; in the same way Tenth Army logistical planners took advantage of their work on the canceled Formosa operation, adapting it to the needs of the Okinawa campaign.39
Out of these planning activities came extremely important decisions that modified and expanded the scope of proposed operations. Tenth Army found it necessary to enlarge the troop list by about 70,000 to include greater numbers of supporting combat elements and service units. Its staff presented and supported a plan for initial assault landings on the west coast of Okinawa, just north and south of Hagushi, as the most feasible logistically and as consonant tactically with the requirements of CINCPOA. The naval staff insisted on the necessity of a sustained week-long naval bombardment of the target and on the consequent need for a protected anchorage in the target area where the fleet units could refuel and resupply. As a result it was decided to capture the Kerama Islands just west of Okinawa, a week before the main landings, and the 77th Division was assigned this task. At the suggestion of Admiral Turner a landing was to be feinted on the eastern coast of the island, and the 2d Marine Division was selected for this operation. The commitment of these two reserve divisions impelled Tenth Army to secure the release of the area reserve division to the Expeditionary Troops, and the 27th Division was designated the floating reserve. In its place, as area reserve, the first Division was ordered to stand by in the South Pacific. Finally, CINCPOA was twice forced to set back the target date because delays in the Luzon operation created difficulty in maintaining shipping schedules and because unfavorable weather conditions appeared likely in the target area during March. L Day (landing day) was set for 1 April 1945.40
As finally conceived, the plan for the capture of Okinawa gave fullest opportunity for the use of the mobility, long range, and striking power of combined arms. After the strategic isolation of Okinawa had been effected by land- and carrier-based aircraft, the amphibious forces were to move forward to the objective. Task Force 52 (the Amphibious Support Force) and Task Force 54 (the Gunfire and Covering Force), assisted by the fast carriers of Task Force 58, were to begin operations at Okinawa and the Kerama Group on L minus 8 (24 March). They were to destroy the enemy defenses and air installations by naval gunfire and air strikes, clear the waters around the objective and the beaches of mines and other obstacles, and provide cover and protection against hostile surface and air units to ensure the safe and uninterrupted approach of the transports and the landings of the assault troops. After the landings they were to furnish naval support and air cover for the land operations.41
Mine sweepers were to be the first units of the Amphibious Support Force to arrive in the target area. Beginning on L minus 8, they were to clear the way for the approach of the bombardment units and then to sweep the waters in the landing and demonstration areas to the shore line.42 Underwater demolition teams were to follow the mine sweepers, reconnoiter the beaches, and demolish beach obstacles.43
Naval gunfire was to support the capture of Okinawa by scheduled destructive bombardment in the week before the landings, by intensive close support of the main and subsidiary landings and the diversionary feint, and thereafter by delivering call and other support fires. The fire support ships with their 5- to 16-inch guns were organized into fire support units, each consisting of 2 old battleships, 2 or 3 cruisers, and 4 or 5 destroyers, that were to stand off the southern part of the island in accordance with definite areas of responsibility. In view of the size of the objective and the impossibility of destroying all targets, fire during the prelanding bombardment was to be laid on carefully selected targets; the principal efforts were to be directed to the destruction of weapons threatening ships and aircraft and of the defenses opposing the landings. Profitable targets were at all times to be sought by close observation, exploratory firing, and constant evaluation of results. Covering fires were to be furnished in conjunction with fire from gunboats and mortar boats in support of mine-sweeping operations and beach demolitions.44
On L Day, beginning at 0600, the naval guns were to mass their fires on the beaches. Counterbattery and deep supporting fires were to destroy the defense guns and keep enemy reinforcements from moving up to oppose the landings. As the assault waves approached the beaches, the fires of the big guns would lift to targets in critical areas inland and to the exterior flanks of the troops. Mortar boats and gunboats were to lead the boat waves to the shore, delivering mortar and rocket fire on the beaches. All craft would begin 40-mm. fire on passing the line of fire support ships and would fire at will until H Hour.45 After the landings scheduled fire on areas 1,000 yards inland and on the flanks would be continued, but top priority would be given to call fires in direct support of the assault elements.46
All scheduled bombardments until H minus 35 minutes were to be under control of the commander of Task Force 52. After that time, because of the size of the landing forces and the extent of the beaches, the commanders of the Northern and Southern Attack Forces would assume control of the support of their respective landing forces. The commander of Task Force 51 was to remain responsible for the general coordination as well as the actual control of bombardment in the Army zone. By 1500 each day he would allocate gunfire support vessels for the succeeding twenty-four hours in accordance with approved requests from Army and Corps.47
MAP NO. 3: The Plan of Attack
MAP NO. 3
Air support was to be provided largely by the fast carriers of Task Force 58 and by the escort carriers of Task Force 52. The fast carriers were for the first time to be available at the target area for a prolonged period to furnish support and combat air patrols. They were to cover mine-sweeping operations, hit targets on Okinawa which could not be reached by naval gunfire, destroy enemy defenses and air installations, and strafe the landing beaches. The escort carriers would provide aircraft for direct support missions, antisubmarine patrols, naval and artillery gunfire spotting, air supply, photographic missions, and the dropping of propaganda leaflets. After L Day additional support was to be furnished by seaplane squadrons based on the Kerama Islands and by the shorebased Tactical Air Force of the Tenth Army.48 The latter was eventually to be responsible for the air defense of the area, being charged with gaining the necessary air superiority and giving tactical support to the ground troops.49
Provision was made for the careful coordination of all naval gunfire, air support, and artillery both in the assault and in the campaign in general. Target information centers, to be established at army, corps, and division levels, would collect and disseminate data on all targets suitable for attack by the respective arms and keep a record of attacks actually carried out. In addition, at every echelon, from battalion to army, representatives of each support arm-artillery, naval gunfire, and air-were to coordinate the use of their respective arms for targets in their zones of action and advise their commanders on the proper employment of the various types of supporting fires. Requests for support would thus be coordinated and screened as they passed up through the various echelons for approval.50
Under cover of the sustained day and night attacks by the naval and air forces, the first phase of the campaign-the capture of the Kerama and Keise Islands and of the southern part of Okinawa-was to begin. On L minus 6, the Western Islands Attack Group was to land the reinforced 77th Division on the Kerama Islands. The seizure of these islands was designed to give the joint Expeditionary Force, prior to the main assault on Okinawa proper, a base for logistic support of fleet units, a protected anchorage, and a seaplane base. Two regimental combat teams were to land on several of the islands simultaneously and to proceed from the southeast end of the group to the northeast by islandhopping maneuvers, capturing Keise Island by L minus 1. All hostile coastal defense guns that could interfere with the construction of the proposed naval bases were to be destroyed. Organized enemy forces would be broken up without attempting to clear the islands of snipers. Two battalions of 155-mm. guns were to be emplaced on Keise in order to give artillery support to the landings on the coast of Okinawa. Then, after stationing a small garrison force in the islands, the division would reembark and be prepared to execute the Tenth Army's reserve plans, giving priority to the capture of Ie Shima 51 (See Map No. 3.)
While the 77th Division was taking the lightly held Kerama Islands, the preliminary operations for softening up Okinawa would begin; they would mount in intensity as L Day approached. Beginning on 28 March fire support units would close in on the island behind the mine sweepers and demolition teams. The Northern and Southern Attack Forces would arrive off the west coast early on L Day and land their respective ground forces at H Hour, tentatively set for 0830. III Amphibious Corps would land, two divisions abreast, on the left flank, north of the town of Hagushi at the mouth of the Bishi River XXIV Corps would land, two divisions abreast, on the right flank, south of Hagushi. The four divisions in landing would be in the following order from north to south; 6th Marine Division, 1st Marine Division, 7th Division; and 96th Division. The two corps were then to drive across the island in a coordinated advance. The 6th Marine Division was first to capture the Yontan airfield and then to advance to the Ishikawa Isthmus, the narrow neck of the island, securing the beachhead on the north by L plus 15. The 1st Marine Division was to head across the island and drive down the Katchin Peninsula on the east coast. South of the Corps' boundary, which ran eastward from the mouth of the Bishi, the 7th Division would quickly seize the Kadena airfield and advance to the east coast, cutting the island in two. The 96th was required initially to capture the high ground commanding its beaches on the south and southeast; then it was to move rapidly down the coastal road, capture the bridges near Chatan, and protect the right of the Corps. Continuing its attack, it was to pivot on its right flank to secure the beachhead on the south by L plus 10 on a line running across the isthmus below Kuba and Futema.52
The choice of the beaches north and south of Hagushi for the initial assault was made after a study by Tenth Army of all the landing beaches in southern Okinawa and a survey of several plans of action. The various plans were weighed in the light of the requirements of the CINCPOA Joint Staff Study and considerations of tactical and logistical feasibility. The preferred plan was finally chosen for a number of reasons. First, it would secure the necessary airfields by L plus 5. Second, it would provide the unloading facilities to support the assault. The Hagushi beaches were considered the only ones capable of handling sufficient tonnage to sustain a force of two corps and supporting troops, and this seemed to outweigh the disadvantages of not providing for the early capture of the port of Naha and the anchorage in Nakagusuku Bay. Third, the plan would result in separating the enemy forces. Fourth, it would concentrate the troops on one continuous landing beach opposite the point where the greatest enemy resistance was expected. Fifth, it would use the terrain least advantageous for enemy resistance to the landings. Finally, it would permit maximum fire support of the assault.53
The scheme of maneuver was designed to isolate the initial objective, the southern part of the island, by seizing the Ishikawa Isthmus, north of the landing beaches, to prevent enemy reinforcement from that direction. At the same time the establishment of a general east-west line from Kuba on the south would prevent reinforcement from the south. Thereafter, the attack was to be continued until the entire southern part of the island was occupied.54 Ground commanders hoped that, for the first time in the Pacific, maneuver could be used to the utmost. The troops would cut across the island quickly, move rapidly to the south, break up the Japanese forces into small segments, bypass strong points, and mop up at leisure.55
While the troops were landing on the west coast, the 2d Marine Division would feint landings on the southeast coast. This demonstration, scheduled for L Day and to be repeated on L plus 1, would be as realistic as possible in order to deceive the enemy into believing that landings would be made there as well as on the Hagushi beaches. After the demonstration the division would be prepared to land on the Hagushi beaches in support of the assault forces.56
The 27th Division, as floating reserve, was to arrive at Ulithi not later than L plus 1 and be on call of the Commander, Joint Expeditionary Force. It was to be prepared to seize the islands off the east coast of Okinawa and then to land on that coast in support of XXIV Corps.57
In case the preferred plan for landing on the west coast proved impracticable, an alternate plan was to be used. In this plan, the capture of the Kerama Islands was to be followed by a similar sweep through the small islands east of southern Okinawa that guarded the entrance to Nakagusuku Bay. On L Day two Marine divisions would land on the southeast coast of Okinawa, between Chinen Point and the town of Minatoga. During the next three days the marines were to seize high ground in the area in order to support a landing by two divisions of XXIV Corps on the lower part of Nakagusuku Bay, between Kuba and Yonabaru. Although the alternate plan met most of the requirements for a successful landing operation, it was distinctly a second choice because it would allow the enemy reserves to offer maximum opposition to the second landings and would require a prolonged assault against all the enemy forces on the island to complete the first phase of the mission.58
Psychological Warfare and Military Government
Despite general skepticism as to the effectiveness of psychological warfare against the Japanese,59 an attitude which resulted from its failure in many previous operations, the American plan called for an intensive effort to weaken the enemy's will to resist. Intelligence agencies prepared 5,700,000 leaflets to be dropped over Okinawa from carrier planes. More millions of leaflets were to be printed at the target and scattered over specific areas by bombs and shells. Tanks with amplifiers, an airplane with an ultraloud speaker, and remotely controlled radios dropped behind enemy lines would also tell the enemy why and how he should surrender.60
The plans for psychological warfare were also directed toward influencing the Okinawans, and in this connection there was greater optimism. Because the Okinawans were of a different stock and culture from the Japanese, and had been treated by their rulers as inferiors rather than as elements to be assimilated to Japanese nationalism and militarism, it was hoped that the civilians would not be as hostile, or at any rate as fanatical, as the Japanese.
The Okinawans also presented the American planners with the problem of military government. The problem was twofold-that of removing the Okinawans from the front lines and that of caring for them; it was necessary to handle the problem in such a way as to facilitate military operations and to make available to the occupying forces the labor and economic resources of the areas. Approximately 300,000 natives lived in southern Okinawa; thousands of others were in the north and on near-by islands. Never before in the Pacific had Americans faced the task of controlling so many enemy civilians.
Basic responsibility for military government in the conquered Japanese islands devolved on the Navy, and Admiral Nimitz was to assume the position of Military Governor of the Ryukyus. However, in view of the fact that most of the garrison forces were Army troops, Admiral Nimitz delegated the responsibility to General Buckner. The latter planned to control military government operations during the assault phase through his tactical commanders; corps and division commanders were made responsible for military government in the areas under their control and were assigned military government detachments whose mission was to plan and organize civilian activities behind the fighting fronts. As the campaign progressed and increasing numbers of civilians were encountered, teams attached to military government headquarters of Tenth Army would assume charge, organize camps, and administer the program on an island-wide basis. During the garrison phase the Island Commander, on order of General Buckner, would exercise command over all military government personnel. Maj. Gen. Fred C. Wallace would act through a Deputy Commander for Military Government, Brig. Gen. W. E. Crist 61
The major problem of Military Government was to feed and provide emergency medical care for the approximately 300,000 civilians who were expected to be within the American lines by L plus 40. Each of the combat divisions mounted out with 70,000 civilian rations of such native staples as rice, soy beans, and canned fish and also with medical supplies. Military Government personnel would land in the wake of assault units to handle a huge "disaster relief" program. Additional supplies of all kinds were to be included in the general maintenance shipments.62
Mounting the Attack
Organizing the Supply Line
The planning and execution of ICEBERG presented logistical problems of a magnitude greater than any previously encountered in the Pacific. For the assault echelon alone, about 183,000 troops and 747,000 measurement tons of cargo were loaded into over 430 assault transports and landing ships at 11 different ports, from Seattle to Leyte, a distance of 6,000 miles. (See Appendix C, Tables Nos. 4 and 5.) After the landings, maintenance had to be provided for the combat troops and a continuously increasing garrison force that eventually numbered 270,000. Concurrently, the development of Okinawa as an advanced air and fleet base and mounting area for future operations involved supply and construction programs extending over a period of many months subsequent to the initial assault. Close integration of assault, maintenance, and garrison shipping and supply was necessary at all times.63
Factors of distance dominated the logistical picture. Cargo and troops were lifted on the West Coast, Oahu, Espiritu Santo, New Caledonia, Guadalcanal, the Russell Islands, Saipan, and Leyte, and were assembled at Eniwetok, Ulithi, Saipan, and Leyte. The closest Pacific Ocean Area bases were at Ulithi and the Marianas, 5 days sailing time to Okinawa (at 20 knots). The West Coast, which furnished the bulk of resupply, was 6,250 nautical miles away, Or 26 days' sailing time. Allowing 30 days to prepare and forward the requisitions, 60 days for procurement and loading on the West Coast, and 30 days for sailing to the target, the planners were faced with a 1120-day interval between the initiation of their calculations and the arrival of supplies. This meant in practice that requisitioning had to be started before a Troop Basis had been fixed and the details of the tactical plans worked out. Distance, moreover, used up ships and compelled the adoption of a schedule of staggered supply shipments, or "echelons," as well as a number of other improvisations. Mounting the troops where they were stationed, in the scattered reaches of the Pacific Ocean and Southwest Pacific Areas, required close and intricate timing to have them at the target at the appointed moment.64
Broad logistic responsibilities for the support of ICEBERG were assigned by Admiral Nimitz to the various commanders chiefly concerned. Admiral Turner, as commander of the Amphibious Forces Pacific Fleet, furnished the shipping for the assault troops and their supplies, determined the loading schedules, and was responsible for the delivery of men and cargo to the beaches. General Buckner allocated assault shipping space to the elements of his command and was responsible for landing the supplies and transporting them to the dumps. The control of maintenance and garrison shipping, which was largely loaded on the West Coast, was retained by CINCPOA. Responsibility for both the initial supply and the resupply of all Army troops was assigned to the Commanding General, Pacific Ocean Areas, while the Commanders, Fleet Marine Force, Service Force, and Air Force of the Pacific Fleet were charged with logistic support of Marine, Navy, and naval aviation units. The initial supplies for the troops mounting in the South Pacific and the Southwest Pacific were to be furnished by the commanders of those areas.65
The first phase of supply planning involved the preparation of special lists of equipment required for the operation, which included excess Tables of Equipment items, equipment peculiar to amphibious operations, and base development materials. Such lists, or operational projects as they were known, had been prepared for the projected Formosa operation; when this was canceled the projects were screened and reduced to meet the needs of ICEBERG.66
At a very early stage in the planning it became evident that there was a shortage of available shipping. The number of combat and service troops included in the initial Troop Basis far exceeded the capacity of allocated shipping. As a result, tonnage had to be reduced for some units while other units were eliminated entirely from the assault echelon and assigned space in the next echelon. Later, in January 1945, it became apparent that there was still not enough shipping space in the assault echelon to transport certain air units and base development materials designed for early use. It was necessary to request CINCPOA to increase the over-all allocation of LST's and LSM's, as well as to curtail cargo tonnage and provide for the quick return of LST's to Saipan to load eight naval construction battalions.67
Providing the assault troops with their initial supplies was not a difficult problem as generally there were sufficient stocks on hand at each of the mounting areas. When the assault units embarked, they took with them a 30-day supply of rations, essential clothing and equipment, fuel, and medical and construction supplies. Initial ammunition quotas consisted of five CINCPOA units of fire.68 On Leyte, XXIV Corps found that SWPA logistics agencies did not have sufficient rations on hand to supply it as required, and the shortage was overcome by having the Corps joined at Okinawa by two LST's loaded with rations from Tenth Army reserve stocks in the Marianas.69
Equipment issued to the troops included weapons and instruments of war never before used against the Japanese. New-type flame-thrower tanks, with an increased effective range and a larger fuel capacity, were available for the invasion. Each division was issued 110 sniperscopes and 140 snooperscopes, devices for seeing in the dark by means of infrared radiation; the former were mounted on carbines and permitted accurate night firing, while the latter were on hand-held mounts and could be used for night observation and signaling. Army artillery and antiaircraft units used proximity (VT) fuzes over land areas for the first time in the Pacific. During the campaign tests were conducted with a new mortar-locating device, the Sound Locator Set GR-6, and the 57-mm.. and 75-mm. recoilless rifles and 4.2-inch recoilless mortars.70
Supplies to maintain the troops at the target were scheduled to arrive twenty-one shipments from the West Coast. Loaded ships were to sail from Pacific ports at 10-day intervals, beginning on L minus 40 (20 February 1945), and to arrive at the regulating stations at Ulithi and Eniwetok beginning , L minus 5, there to await the call of General Buckner. These maintenance; shipments, planned to provide automatic resupply until L plus 210 (31 October 1945), were based on the estimated population build-up at the scheduled time of arrival. The principal emergency reserves were kept at Saipan and Guan. 71
The main logistical task of the operation, in Admiral Nimitz's opinion, v. the rapid development of air and naval bases in the Ryukyus to support further operations against Japan. The Base Development Plan for Okinawa, published by CINCPOA, provided for the construction of eight airfields on Okinawa, two of which were to be operational by L plus 5, a seaplane base, an advanced fleet. base at Nakagusuku Bay, and the rehabilitation of the port of Naha to accommodate support shipping. Base development responsibilities also included immediate support of the assault by the early construction of tank farms for the bulk storage of fuel and for the improvement of waterfront unloading facilities and of roads. Later a large construction program was planned that included roads, dumps, hospitals, communications facilities, water supply systems, and housing and recreational facilities. A plan for the development of Ie Shima as an advanced air base was also prepared.72
General Buckner was charged with the responsibility for base development in the Ryukyus. Assigned to Tenth Army for the execution of the Base Development Plan was the Island Command Okinawa, or Army Garrison Force, with Maj. Gen. Fred C. Wallace in command. Some of the Island Command troops were to land in the assault echelon and to provide logistic support for the assault troops during and immediately after the landings. At the conclusion of the amphibious phase, the Island Command was to act as Tenth Army's administrative and logistical agency, operating in effect as an Army service command and an advanced section of the communications zone. As such, it was to be in charge of the base development program as well as of the garrisoning and defense of the captured positions. Garrison troops and base development materials were scheduled to arrive at Okinawa in seventeen echelons. These were based primarily on the unloading capacity of the Hagushi beaches; the tonnage in each echelon was kept within the estimated discharge capacity between the arrivals of the echelons. Most of this garrison shipping was loaded on the West Coast and Oahu, but some originated in the South Pacific and the Marianas.73
Training and Rehearsal of Troops
The great distances that separated the elements of its command, together with the limited time available, precluded combined training or rehearsal by Tenth Army of the maneuver which would land two corps abreast on a hostile shore. To the extent that circumstances permitted, however, the scattered units of the Tenth Army engaged in individual training, combined-arms training, and special training in amphibious, cave, and mountain warfare. Particular efforts were made to train ground troops in the use of the new snooperscopes and sniperscopes, and the one standard tank battalion which was converted to an armored flame thrower battalion received instruction in the use and maintenance of its tanks. Many service units received little specialized training because of the pressure of their regular duties and, in some cases, the circumstance that they had been released to Tenth Army only a few days before mounting from Hawaii.74
When, in December 1944, XXIV Corps received its warning order, it was in action over a large part of southern Leyte, engaged in virtually separate operations on the east and west coasts of the island. The Corps was not released from tactical responsibility until 10 February 1945, and it did not complete the assembly of all its units in the staging area at Dulag until 18 February. Training and rehearsals had to be sandwiched between the rehabilitation program for its combat-weary units and the mounting-out for the new operation. The 7th, 77th, and 96th Divisions were able to engage only in a very limited amount of training specifically oriented to the Okinawa operation, but all managed to train in the use of the sniperscope and of flame throwers. The Corps was, however, able to engage in a full-scale nonfiring rehearsal with the 7th and 96th Divisions and amphibious elements of the Southern Attack Force in Leyte Gulf from 15 to 19 March 1945. In addition to training in the techniques of amphibious landings, the troops practiced the breaching and scaling of sea walls. Assault regiments of the two divisions landed and moved inland for 1,000 yards in a simulated attack, after which critiques were held and the exercise repeated. The 77th Division conducted practice landings separately in Leyte Gulf from 9 to 16 March. The 27th was able to engage in intensive training in Espiritu Santo between October 1944 and 25 March 1945, when it embarked for the target; four landing rehearsals were also held between 20 and 25 March.75
All the Marine divisions scheduled for the Okinawa campaign had several months in which to train and rehearse. The 1st Marine Division, finding training facilities restricted in the Russell Islands, arranged for each of its regiments to take a month's training on Guadalcanal, where adequate artillery, mortar, and small-arms ranges were available. The 6th Marine Division trained on Guadalcanal, conducting numerous division problems and field exercises. On Saipan the 2d Marine Division had the advantage of practicing against the Japanese still holed up in the hills. The III Amphibious Corps conducted a combined rehearsal with the 1st and 6th Marine Divisions at Guadalcanal from 2 to 7 March; full-scale problems were worked out, troops and token supplies were landed, and a communications net established.76
Mounting Out
Responsibility for the loading of the assault units was decentralized through delegation to the commanders at the various mounting points; the Commanding General, Tenth Army, however, retained control of the mounting of units from Oahu. The commanders of the III Amphibious Corps and XXIV Corps were responsible for embarking their respective troops in the South Pacific and Leyte. The 2d Marine Division supervised the loading of its own troops and other units mounting from Saipan. Units which originated on the West Coast were moved to the assigned mounting points for integration with the assault echelon.77
All loading was conducted according to the transport doctrine of the Amphibious Forces Pacific Fleet and the logistical directives published by Tenth Army. One transport squadron of fifteen APA's (transports) and six AKA's (cargo ships), together with the requisite number of LST's and LSM's, was allocated to each division, and additional allocations were made for Corps and Army troops. (See Chart IV.) Altogether, 111 APA's, 47 AKA's, 184 LST's, and 89 LSM's were loaded in mounting the joint Expeditionary Force. Transport Quartermaster Teams were activated and assigned to Army units to load their troops and equipment, while Marine units used the teams which had functioned in previous operations. Admiral Turner also sent two combat loading teams, trained in embarkation procedures and familiar with the policies of his command, to aid in the loading of the two corps at Leyte and the GuadalcanalRussells area. and of the 27th Division at Espiritu Santo. All loading plans and operations were subject to the approval of the captain of each ship as well as of the transport squadron commander concerned.78
Tenth Army headquarters and most of its attached troops mounted out of Hawaii, while the 7th, 77th, and 96th Divisions embarked at Leyte, where the largest number of ships was loaded. Each division did its own loading under general supervision of the Corps. The chief difficulty encountered was the necessity of loading across the open beaches in the Dulag area on the east coast of Leyte. Piers were nonexistent or of too flimsy a construction to withstand the battering which they took in the high surf and tide. LST's and LSM's were beached as near shore as possible and vehicles had to be driven through the water; 105-mm. artillery was loaded by means of DUKW's and ponton causeways. Transports were loaded in the stream by ships' boats, LCT's, and LSM's. Many lighters and landing craft on Leyte had been diverted to the needs of the Luzon campaign in February when loading began, and a hurry call was sent to Tenth Army for additional lighterage. Loading plans also went awry because of the lack of accurate advance information on the characteristics of ships to be loaded. Much time was consumed by the necessity of unloading newly arrived supplies across the open beaches and reloading them in the assault shipping. The 27th Division loaded separately at Espiritu Santo, where it met difficulties of transportation and misunderstandings with naval officials.79
Photo: LOADING SUPPLIES FOR OKINAWA
LOADING SUPPLIES FOR OKINAWA-not only arms, ammunition, and food but also
great quantities of construction material (above). Barrels of fuel and boxes of other
matériel are shown below being loaded at Leyte.
Photo: LOADING SUPPLIES FOR OKINAWA
III Amphibious Corps and its units mounted out in the GuadalcanalRussells area. Loading was out in the stream but was facilitated by an ample supply of lighterage and by excellent sandy beaches. Assault troops were embarked on transports initially and were transferred to landing ships at the staging point at Ulithi, a method which shortened the time to be spent in the uncomfortable, crowded LST's and LSM's.80
Movement to the target got under way on 18 March 1945, when the slow tractor group carrying the assault troops which were to take the Kerama Islands left San Pedro Bay, Leyte. Transports with other 77th Division troops sailed from Leyte three days later, and the remainder of the division followed on 24 March. The tractor groups of the Southern Attack Force sailed from Leyte on 25 March, and the faster transports followed two days later. The course from Leyte was approximately NE by N to a point about 300 miles south of Okinawa, when it was changed to N by NW directly to the target. Units of III Amphibious Corps in the Northern Attack Force sailed from the Guadalcanal area on 12 March, arriving on 21 March at Ulithi, where four days were spent in topping off supplies and effecting the transfer of troops to landing ships. The Northern Tractor Flotilla left from Ulithi on 25 March. The tractor groups carrying the 2d Marine Division to the demonstration beaches left Saipan the same day. When the remainder of the Northern and Southern Attack Forces and the Demonstration Group set forth on 27 March, Americans and Japanese were already engaged in land fighting in the Kerama Islands.81
CHART IV
XXIV Corps Assignment of Shipping for the Assault on Okinawa
[Click for larger image as a PDF file]
CHART IV: XXIV Corps Assignment of Shipping for the Assault on Okinawa
Source: XXIV Corps Action Report Ryukyus, 1 April to 30 June 1945, chart opp. p. 21
page created 10 December 2001
Endnotes
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