Operation Iceberg: The Assault on Okinawa - The Last Battle of World War II (Part 1) April - June 1945

The Americans Look at the Options
The Ryukyu Islands
The Japanese Prepare
The Opposing Forces (1): The Japanese
The Americans Prepare
The Opposing Forces (2) - The Americans
US Navy
US Army
US Marine Corps
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Okinawa Okinawa Okinawa Okinawa Okinawa Okinawa Okinawa Okinawa Okinawa
Okinawa - Ryujyu Islands Okinawa - Central Pacific Task Forces Okinawa - Expeditionary Troops Organisation Okinawa Okinawa Assault Okinawa Island Group Allied Organisation Southern Okinawa
Illustrations courtesy of the US Army's Center for Military History


The spring of 1945 found the Allies' fortunes very much on the rise. In Europe, the Allied armies were now closing in on the Reich with the offensive against the Rhineland and crossing of the Rhine in the West, the isolation of East Prussia and drive on eastern Germany by the Soviet Union and the continued advance into northern Italy. In the Pacific, a serious of campaigns had reclaimed many of the territories occupied by the forces of Imperial Japan, while isolating many others. There was little doubt as to which side was going to be the final victor, it was just a question of how many more people would die and where the final battle would be.

The Allied advance across the Pacific entailed two major thrusts and a subsidiary one. The subsidiary one was a combined American / Canadian advance that had cleared the Japanese from the Aleutian Islands and was looking to move southwest. In the Southwest Pacific Area, General Douglas MacArthur with a combined force of US Army, US Marines, Australians and New Zealanders had seized the Solomon Islands, then New Britain and advanced along New Guinea's northern coast towards the Philippines. MacArthur invaded Leyte on 20 October 1944 and Luzon on 9 January 1945, with the support of the Third and Seventh Fleets and land-based aircraft. The Philippines were finally declared secure on 5 July 1945, two weeks after Okinawa. In the Central Pacific Area, the Fifth Fleet, supported by carrier-based aircraft had secured the Gilberts in late 1943 and neutralised the Japanese strongholds of Rabaul and Truk. They seized the Marshalls in early 1944, the Mariana Islands by the end of August 1944, the Palau Islands by the end of November 1944, and Iwo Jima by the end of March 1945. The seizure of the Marianas (given to the Japanese as Mandates in 1919 by the League of Nations as former possessions of Imperial Germany) was a serious blow to the Japanese who considered them to be a key part of the Empire. It caused such an outcry as to force the then Prime Minister General Shigenori Tojo to resign and a new cabinet to be formed.

It was obvious to everyone what was coming next. For the invasion of the homeland, the Japanese knew the Americans would need a large base as a staging post from which to strike. On the other side, the Americans knew that an attempt to land on the main Japanese islands (the overall codename for which was Operation Downfall) would be met by several million soldiers, militia and civilians all of whom would offer fanatical resistance in the same vein as Tarawa, Peleliu and Iwo Jima. Careful preparation and a large logistical base were therefore necessary. The question was, would it be Formosa off the coast of mainland China or would it be Okinawa, part of the Ryukyu Islands?

The Americans Look at the Options

Almost a year before the invasion of Okinawa in May 1944, Admiral Ernest B King (Chief of Naval Operations and Commander-in-Chief, US Navy), Admiral Chester W Nimitz (Commander-in-Chief, Pacific Fleet and Commander, Pacific Ocean Area) and Admiral William F Halsey (Commander, Third Fleet) met in San Fransisco to discuss the direction of Pacific Theatre strategy. There was a concern that Japan might conclude a separate peace with a hard-pressed China but if the US was to establish bases on the Chinese coast and supply the large but ill-equipped Chinese Army then the Japanese would have to reinforce their forces on the mainland with the result that they would become stretched even further. They considered an invasion of Formosa (present day Taiwan) before it could be reinforced, by bypassing the Philippines. There were certain advantages to this in that the bypassing of the Philippines would remove the probability that US forces would become involved in a protracted campaign, would provide a base from which to invade the mainland, protect the supply routes to China and provide a base from which to operate B-29 Superfortresses that was closer than the ones they currently had in southern China. The disadvantages though were that it was within range of Japanese airbases in China, was large (240 miles by 90 miles) and had mountainous terrain, had a substantial garrison of its own, that being the 10th Area Army under General Rikuchi Ando with 479,313 troops of the 9th, 12th, 50th, 66th and 71st Divisions, 8th Air Division, 1st Air Fleet (Imperial Japanese Navy - IJN), 12th, 75th, 76th, 102nd and 103rd Independent Mixed Brigades (IMBs) that could easily be reinforced. Operation Causeway promised to be a tough campaign - Formosa was about the same size as Kyushu, the southernmost Japanese island.

In July 1944 as the Marianas campaign was coming to a close, President Franklin D Roosevelt met with Admiral Nimitz and General Douglas MacArthur. As part of the discussion, MacArthur voiced his opposition to the proposals to bypass the Philippines and argued that with additional naval support he could take them back successfully. Nimitz therefore agreed to alternate plan which saw the assault on the Philippines commence in October 1944, with the expectation that much of it would be recaptured by December. Depending upon the exact situation at the time, either Luzon would be invaded in February 1945, or the Formosa - Amoy (on the mainland) area in March 1945, followed by the Bonins (Chichi Jima) in April and the Ryukyus (that included Okinawa) in May.

Soon after the plan was developed, Lt General Millard F Harmon, Army Air Forces, Pacific Ocean Area, argued that Causeway be abandoned as air operations could be more effectively be conducted from the Marianas, as there would still be a threat from remaining Japanese forces on Formosa (it wouldn't be possible to completely occupy it as it was so large), possible interception from the Chinese mainland along the entire route to Japan, and less favourable weather. Harmon proposed that Iwo Jima in the Volcano Islands be seized in January 1945 and Okinawa in June, simultaneously with a strike at Luzon. General Robert C Richardson, US Army Forces, Pacific Ocean Area agreed with the idea, as did General Simon B Buckner, Commander, US Tenth Army and Admiral Raymond A Spruance.

In October 1944, Nimitz advised Admiral King of the various views that had been expressed and the Joint Chiefs of Staff evaluated the various proposals. They eventually directed MacArthur to land on Luzon on 20 December 1944 and Nimitz to land on Iwo Jima on 20 January 1945 and Okinawa on 1 March 1945. These final operations before the invasion of Japan, the first phase of which was targeted against Kyushu (Operation Olympic) and scheduled for November 1945, were codenamed Detachment (Iwo Jima), Iceberg (the overall operation), Bunkhouse (the Ryukyu Islands) and Scattering (Okinawa itself). The securing of the Philippines would mean that Japanese forces in the Dutch East Indies would be cut off from the home islands. B-29s could continuously bomb Japan from their bases in the Mariana Islands and the seizure of Iwo Jima and Okinawa would mean that the Japanese would not have bases directly in their flight path from which to intercept them and provide bases from which the Americans could provide the bombers with fighter protection and emergency airfields that damaged bombers could land on. It would also mean additional flank protection as the Americans would be in a better position to stop Japanese aircraft from Formosa and China intercepting the bombers. The Americans retained the command structure devised for Formosa for the invasion of Okinawa. MacArthur's advance on the Philippines continuing unabated with the invasion of Leyte in October 1944. The attack on Luzon began on 9 January 1945, while Iwo Jima was assaulted by the three Marine divisions of the III Amphibious Corps (3rd, 4th and 5th) on 19 February, both operations starting a month late due to operational reasons. The main phase of Iceberg, the assault on Okinawa Gunto, would therefore begin on 1 April 1945.

The Ryukyu Islands

The Ryukyu Islands (formerly called the Ryukyu Retto, Retto meaning archipelago) form the majority of the islands (the entire group being called the Nansei Shoto, Shoto meaning groups of islands) that run in a gentle curve between the southernmost of the Japanese home islands, Kyushu, and Formosa. The Ryukus consist of some 161 islands in five major groups - Osumi, Torkara, Amami, Okinawa and Sakishima Guntos (Gunto meaning group), Okinawa Gunto being the largest. The name Ryukyu derives from the Chinese word Liuchiu, meaning something approximating 'precious floating stones on the horizon', and the Japanese inability to pronounce the letter 'L'. It is made up of a number of separate islands and groups: Kerama Retto (eight islands some fifteen miles west); Kume Shima (Shima meaning island, some fifty-five miles west); Agunia Shima (forty miles west); Ie Shima (four miles west); Iheya Retto (four islands, fifteen miles north); Yoron Shima (fifteen miles northeast); and a group of unnamed islands, five to ten miles to the east (called the Eastern Islands by the Americans).

Okinawa Gunto is around 320 miles southwest of Kyushu, 350 miles southeast of Formosa and 450 miles east of mainland China. For a long time, starting in the 6th Century, it was regularly raided by the Chinese who never attempted to gain complete sovereignty over the islands but would occasionally demand tribute. The islands also had relations with Japan but managed to retain some sort of independence from both its neighbours until the 1500s when Japan took partial control. The Japanese invaded the islands and devastated Okinawa in 1609 after it refused to provide troops for Japan's war in Korea. Commodore Matthew Perry used it as a supply base in his attempts to establish trade with Japan in 1853. He in fact raised an American flag on a hill near Shuri Castle that Americans would die some 92 years later. As Japan opened up, it quickly became a major regional player and took control of Okinawa in 1867, giving the King a permanent residence in Tokyo. It installed a governor in 1879 after the Japanese Home Ministry took control of it in 1874 and gave it prefecture (ken) status. This quickly became a source of tension between Japan and China and the Okinawans preferred their semi-independent status between the two powers, but they were now a Japanese imperial possession. They were granted a prefecture assembly and a seat in the Diet (Japanese Parliament) in 1920, while it was consolidated into the Home Islands District of Kyushu in 1943.

Okinawa Shima runs northeast to southwest, is sixty-four miles in length and varies between two miles (at the Ishikawa Isthmus) and eighteen miles (Motobu Peninsula) in width. A number of smaller peninsulas extend from the southern portion of the island that afford a number of superb anchorages and the Ishikawa Isthmus divides the island in terms of terrain. The north has rugged terrain with 1,000 - 1,500 ft ridgelines coming off a central hill, with deep ravines and gullies in-between them leading to a coastline replete with steep cliffs. The Motobu Peninsula is the central dominant feature in the north and consists of dense forests of pine, oak and thick underbrush and was utilised by the Japanese as their main area of resistance, especially as the transportation network was very limited and cross-country movement was very difficult. The soil is red clay and sandy loam, but is well drained by a large number of streams and small rivers. The south on the other hand, held the majority of the population and the terrain consisted of gently rolling hills that climb to a height of over 500 feet at the southern end. They were cut by a large number of ravines and gullies, under which there were lots of caves (gama) cut by underground streams that provide limited drainage to the hills. These hills could be steep and small knolls were scattered throughout the area, while escarpments and limestone ridges provided successive, mutually supportive defence lines especially suited to the shorter-range Japanese weapons. While there were areas of light woodland, around eighty percent of the south consisted of cultivated farmland, which provided the main industry, alongside fishing. The transport infrastructure, while better than the north, was still nowhere near compatible to that in Europe, Japan or the USA. The poor drainage meant that most roads were incapable of taking military traffic during the rainy season and off-road movement was difficult at best. A narrow-gauge (sixty centimetres) railway connected Naha, Kobakura, Kobuba and Yonabaru with branch lines going out from Kobakura to Kadena and Kokuba to Itoman.

Most of the coastline consisted of limestone cliffs, while the best landing beaches were on the west coast, just south of the Ishikawa Isthmus and these were selected due to their proximity to the Yontan and Kadena airfields. The Americans called them the Hagushi Beaches (the Japanese called them the Kadena beaches) after the central Hagushi Village at the mouth of the Bishi Gawa (stream) - Hagushi actually being a mistranslation, the real name of the village being Togushi. The beaches sloped gently and had few natural obstacles (although there were quite a few sea walls that varied between three and ten feet in height), were not continuous but separated by low headlands into sections 100 - 900 yards wide. Low ground that rose gently to some 50 feet lay behind the beaches and had very little cover for anyone advancing off the beaches.

The population of Okinawa at the time numbered some 435,000 and included a large number of Japanese Government officials. Naha was Okinawa's prefectural capital, a large commercial centre and the island's main seaport with a population of over 60,000. Shuri was slightly smaller and was Okinawa's traditional capital, having Shuri Castle (the ancient throne of the Ryukyun kings) overlooking it on a massive ridge cutting right across the island - it would become a hotly contested battleground later in the campaign. Most of the population was spread between villages that varied between 100 and over 1000 in number and the towns of Itoman, Nago and Yonabaru were simply large villages with a few modern buildings. The majority of dwellings were one or two-storey buildings that were either wood or clay and surrounded by low stone walls. One feature that was unique to Okinawa was the stone lyre-shaped family tombs that were a central part of the local animistic cult that emphasised the veneration of one's ancestry. The two main airfields were located on the central plains while Machinato Airfield was just north of Naha while the abandoned Yonabaru Airfield was just across from it on the East Coast. Incidentally, the Imperial Japanese Navy had an airfield on the Oroku Peninsula and two airfields were on Ie Shima.

Temperatures for the island are moderate with a winter low of 4.4 °C (40 °F) while at the time of the campaign (April - June) it ranged in the 70s and 80s (°F) during the day. Humidity is high all year round, and rain, while frequent, is heaviest between May and September and would have a major impact in the coming campaign. In fact, Okinawa can be subject to the occasional typhoon or two between May and November (two serious ones hit Okinawa in September and October that would have disrupted preparations for Operation Downfall).

The Japanese Prepare

Now facing the final onslaught from the Americans, the Japanese prepared to fight the penultimate battle in the hope that they could fight the Americans to a stalemate and sue for peace. Japan had begun the Pacific War with an army that was based around a light infantry doctrine that was validated in China and the early victories in the Pacific against unprepared or lightly armed opponents. The defeats in the Solomons and New Guinea soon forced the Japanese to consider a change to their initial strategy, as did the failure to stop the Americans on the beach with 'impregnable defences', in the Gilberts, Solomons and Marianas, which were simply crushed by overwhelming firepower, material and high esprit de corps. The senseless banzai charges designed to overrun a demoralised enemy simply hastened the destruction of the defending force under American firepower. The third strategy was introduced on Peleliu and followed on Iwo Jima that looked to prolong the fighting as long as possible and gradually grind down the Americans as they assaulted successive lines of defence established in depth across the island. It was designed to extract the maximum price in men and material from the enemy and break their morale and fighting spirit. No banzai charges were seen on Peleliu or Iwo Jima and none would be seen on Okinawa - any attacks would be carefully co-ordinated and carefully planned affairs.

After Truk was neutralised by airpower, the Japanese laid plans for the Ten-Go Operation, which envisaged the creation of a network of mutually supporting airfields that would enable Japanese airpower to destroy any American forces that venture into their defence zone. Thirteen groups of airbases were established throughout the Ryukyu Island chain and on Formosa. After the Marianas fell, the Ten-Go Operation was suspended and a new plan, Sho-Go 2, was put in place, which envisaged massive air attacks coming from the Home Islands, Formosa and the Philippines if the Ryukyus were attacked. The 32nd Army was created on Okinawa and reinforced throughout the summer to eventually boast three infantry divisions, an independent mixed brigade and numerous service and support troops. Lt General Mitsuru Ushijima was appointed its commander in August. A calm, take-charge officer, Ushijima stood in stark contrast to Lt General Isamu Cho, Chief of Staff, who was as equally talented but was an aggressive, hot-tempered officer who tended to push his subordinates to the limit. Colonel Hiromechi Yahara was the senior staff officer in charge of operations and the only member of the senior staff to survive the campaign.

As preparations were underway, the 32nd Army learnt that the 9th Division (its best formation) was going to be transferred firstly to Leyte and then to Formosa under the direct control of the 10th Area Army - a move still hotly debated by Japanese historians. The 9th was formed in 1895 and fought in the 1904 - 5 Russo-Japanese War as well as in China from 1937 to 1939 and consisted of the 7th, 19th and 35th Infantry Regiments, and the 9th Mountain Artillery Regiment. Additional forces were sent to Amami Gunto while other Nansai Shoto islands were defended by the 21st Independent Mixed Regiment (Amami O Shima), 64th Independent Mixed Brigade (Tokuno Shima), 28th Division (Sakishima Gunto) 60th IMB (Miyako Jima), 59th IMB (Irabu Jima) and 45th IMB (Ishigaki Jima). American air and naval power destroyed the few remaining Japanese aircraft on Okinawa before Iceberg commenced, the rest having been transferred to Kyushu and Formosa. The Americans would however, face both conventional air attacks and the Kamikaze ('Divine Wind') that included both aircraft and specially built boats (codenamed Kikusui - floating chrysanthemums) if the Americans invaded Okinawa. Imperials General Headquarters (IGHQ) wanted the 32nd Army to pursue a policy of 'decisive battle' to aggressively close and attack the enemy and defend the airfields but the 32nd Army chose to pursue a 'battle of attrition' against the Americans. Even if the 84th Division had arrived as promised (it didn't), it was unlikely that the 32nd Army would have been able to defend the landing beaches and the airfields, let alone the entire island, and so Ushijima decided to concentrate on the southern third of Okinawa. To appease the 10th Area Army, he deployed the 44th IMB on the plains to defend the airfields in December 1944. Yahara looked at the deployment and considered that the Army units were still stretched too thin and so Ushijima relocated the 44th IMB in January 1945 to cover some of the 62nd Division's sector. The 32nd Army was therefore deployed thus:

There was little faith placed in the promise of air support coming from the Home Islands and so the 32nd Army resorted to building a complex and extensive series of overlapping and mutually supporting defence lines that would be improved throughout the battle. It involved the construction of thousands of bunkers, blockhouses, pillboxes, weapon emplacements and fighting positions. Terrain features were incorporated wherever possible into the defence lines and supplies and munitions protected in dugouts and caves. Some sixty miles of tunnels were dug to protect the 32nd Army.

A few weeks before the invasion, the 32nd Army was alerted by IGHQ that Admirals Nimitz and King had held a conference in Washington in early March - Formosa or Okinawa was the likely target. The Japanese had found that new operations tended to follow between twenty and thirty days after such high level conferences, so the next operation would follow very shortly. They were not to be disappointed.

The Opposing Forces (1): The Japanese

For much of the war, Okinawa Gunto was defended by the battalion-size Fortress Artillery Unit and a small infantry force. On 1 April 1944 (exactly a year before the American landing) the 32nd Army was created, with the veteran 17,000-man 9th Division arriving in June 1944 from Manchuria, along with the battered 44th IMB. The 15th IMR arrived in July followed by the 24th Division from Manchuria and the 62nd Division from China in August. The Imperial Japanese Army's largest formation for deployed operations was the army group (usually a named major regional command) consisting of two or more area armies (usually a named or numbered area command). An area army (for example, the 10th Area Army) was made up of two or more armies and an air army, while an army (for example, 32nd Army) was equivalent to an American or British army corps and made up of two or more divisions (Shidan), one or more IMBs and numerous support troops. Divisions were based on one of two quite different structures - one was made up of three regiments (each of three battalions, similar to the Americans), the other was a two-brigade division, which was formed early in the war to conserve manpower but retain firepower. Regiments and brigades were made up of battalions, with IMBs and IMRs tending to have more than regiments or brigades within divisions. The nondescript term 'unit' was encountered quite frequently and could be used to describe a formation that ranged from a platoon to a battalion or larger in size. Certain combat and support 'regiments' (such as tank, reconnaissance, engineer and transport) were actually battalion size (from three to five companies) but did not have a battalion structure.

Despite the removal of the 9th Division, Ushijima still had some 110,000 troops available to him. This included:

Many of the infantry regiments and battalions varied considerably in organisation and strength but among the combat support units there were broad similarities. Regimental gun companies tended to have four 75mm Model 41 infantry guns, while regimental and battalion antitank companies usually had four to six 37mm Model 94 antitank guns (they were in actual fact rapid-fire infantry support guns). Battalion machinegun companies usually consisted of eight or twelve 7.7mm Model 92 heavy machineguns (tripod-mounted) while the gun companies had four 70mm Model 92 infantry guns, sometimes having 81mm Model 97 mortars instead, and gun units had two. Rifle companies varied widely as well - at full strength they had three rifle platoons, each with three 13 - 15-man sections (with a Model 11, 96 or 99 bipod-mounted light machinegun and one or two 50mm Model 89 grenade dischargers - 'knee mortars') and a 13 - 15-man grenade discharger section with three 'knee mortars'. Rifle companies in the larger battalions quite often had a weapons platoon with two heavy machineguns and two 20mm Model 97 antitank rifles.

The Americans Prepare

The Joint Expeditionary Force (Task Force 51) faced a daunting challenge - they had to draft and develop plans for Iceberg while at the same time strenuously try and obtain detailed intelligence on the terrain of, and Japanese dispositions on, Okinawa. The initial photographic reconnaissance took place in September 1944 and contour lines from captured Japanese maps were used but it wouldn't be until halfway through the campaign itself that complete maps would become available. Intelligence estimates on enemy strength and dispositions were fairly accurate, although somewhat on the low side, with an estimate of 75,000 troops in 2½ divisions, concentrated in the southern third of the island.

Planning began in September 1944 and initially developed a three-phase plan under the assumptions that with B29s flying from the Marianas, the seizure of Iwo Jima and continued carrier strikes on the Home islands would concentrate most of the available Japanese aircraft there. The invasion of Okinawa would probably provoke violent air attacks on the fleet and one of the main early objectives would be the seizure of the Yontan and Kadena airfields so that land-based airpower could help provide protection for the fleet. Phase I involved landing on the western beaches and the early seizure of southern Okinawa with the development of the airfields as well as a number of the offshore islands. Phase II would see the seizure of the rest of Okinawa and Ie Shima (codename Indispensable) with other islands in the Ryukyus. Phase III would see Kikai Shima being assaulted by the 1st Marine Division and Miyako Shima in Sakishima Gunto near Formosa being attacked by the V Amphibious Corps. As it turned out, after Iwo Jima, V Amphibious Corps was in no state to undertake the operation but Phase III was eliminated from the final draft of the plan due to logistical considerations on 6 January 1945 and Phases I and II were not only modified but swapped.

The new Phase I would see the 77th Infantry Division seize Kerama Retto (15 miles west) almost a week before the main landings, which would provide an excellent resupply anchorage for the ships providing supporting fire for the invading forces and a seaplane base for conducting anti-submarine patrols. An Army battalion would seize Keise Shima (11 miles southwest) a day before the main landing and a field artillery group's long-range guns would be emplaced on there. An elaborate demonstration would begin two days before the Kerama Retto operation and involve minesweepers (covered by fighters) clearing the approaches and battleships engaging shore positions. In addition, the 2nd Marine Division would conduct a feint off the beaches in the hope that the Japanese would move forces south to reinforce the threatened area. The main landing would commence at 08.30 (H-Hour) on the 1 April 1945 (D-Day). It would be the largest simultaneous amphibious landing of the Pacific War with two Marine and two Army divisions landing abreast on eight miles of beach. From north to south, III Amphibious Corps (IIIAC) would land opposite Yontan Airfield with 6th Marine Division landing on the left and then moving rapidly inland to seize the airfield and protect the left flank of the Tenth Army by severing the island in two across the Ishikawa Isthmus. The 1st Marine Division would land and maintain contact with XXIV Corps on its right flank. IIIAC artillery would land in two groups of three battalions, with each group supporting a division. The XXIV Corps, separated from the IIIAC by the Bishi Gawa (stream), would land to the south of IIIAC with the 7th Infantry Division maintaining contact with IIIAC on its left and aiming to seize Kadena Airfield while the 96th Infantry Division would land to the south of the 7th. The Corps artillery would land as necessary to support the Corps attack. The Corps would, after securing Kadena Airfield, swing south and secure a line running east to west through Kuba Saki and seal off the Japanese in the south of the island. In detail, the landings from north to south would consist of:

Once the island had been cut in half, the main concentration of Japanese forces isolated in the south and the logistic build-up underway, the XXIV Corps would advance south (7th Inf Div to the east and 96th Inf Div to the west) to seize the southern end of the island. IIIAC would backup the XXIV Corps as necessary with the 1st Mar Div occupying the central part of the island and the 6th Mar Div advancing north. The 77th Inf Div would seize Ie Shima when released and the 27th Inf Div would land when necessary as XXIV Corps' frontline lengthened. Fourteen escort carriers would provide the initial air support, but some 220 Marine fighters would be moved ashore (as well as additional land-based air power) once airfield facilities could accommodate them. The US Navy's Task Force 51 would transport and deliver the landing forces to their destination, sustain them ashore, provide air cover and close support as well as naval gunfire support. The Fifth Fleet's Fast Carrier Striking Force (TF 58) and the Royal Navy's Carrier Force (TF 57) would attack Japanese airfields on Formosa and the Home Islands as well as other areas of the Ryukyus and engage any remnants of the Imperial Japanese Fleet that might sortie. With these additional forces, there were in total, some 1,300 ships committed to Operation Iceberg. The Twentieth Air Force would continue to pound Japan from the Marianas, particularly airfields, and the Pacific Submarine Force would form a cordon between Okinawa and Japan.

The logistic effort required to sustain this size of campaign was enormous. Units that were participating in the operation, staged at a diverse range of locations including Espíritu Santo, Guadalcanal, the Russell Islands, the Marianas, New Caledonia, Leyte, Oahu and the USA. Most formed up at Ulithi (seized during Operation Stalemate II), which was itself over 1,000 miles to the southeast of Okinawa, while the remainder travelled directly from Leyte. It was not only a question of supplying the forces that were to take part in the operation but also sustaining these far-flung bases and their garrisons and maintaining a supply line some 4,000 miles or seventeen days steaming from Pearl Harbor or some 6,200 miles or 26 days steaming from the West Coast. Planners had to consider not only the sustainment of all the combat forces but of the 458 ships that were required to support them, and the ability of the beachhead to handle both troops and supplies. As it was, ammunition expenditure rates would be so high (over three times that seen on the Marianas) that there would be shortages right across the Pacific. Four major airfields would be constructed on Okinawa and have great infrastructure consequences for the island - they would be far more capable than the basic strips the Japanese had built. The port of Naha would be greatly expanded and modernised and a major advanced fleet operating base would be constructed at Nakagusuku Wan. These and other projects would be constructed to launch an even larger venture - Operation Downfall, the invasion of Japan.

The Opposing Forces (2) - The Americans

US Navy

Task Force 50, was part of the Fifth Fleet, Central Pacific Forces under Admiral Raymond A Spruance. Spruance, as the commander directly responsible for the invasion of Okinawa, controlled three major formations:

US Army

The major US Army formation in Operation Iceberg was the Tenth Army, activated on 20 June 1944 at Fort Sam Houston, Texas. It transferred to Schofield Barracks, Oahu, Hawaii in August to prepare for Iceberg. The Tenth Army comprised two Corps, one Marine and one Army, and uniquely, controlled its own tactical air force, which was a joint Army and Marine command. The Tenth Army had some 102,000 Army personnel (38,000 were non-divisional artillery, combat support and headquarters troops and 9,000 were service troops), 88,000 Marines and 18,000 Navy personnel for a total of some 208,000 personnel. The 53rd Anti-Aircraft Artillery (AAA) Brigade was directly under the command of Tenth Army and had five AAA groups, six 90mm and three 40mm battalions. All the units had more than their usual share of weapons and manpower due to Okinawa's proximity to Formosa and Japan. It also had the 51st Military Police Battalion that was assigned in anticipation of the increased pressure from traffic control, guarding prisoners of war, refugees and rear area security, as well as the 80th Medical Group (96th and 153rd Medical Battalions) and 20th Armoured Group (713th Tank Battalion). The two main subordinate formations of the Tenth Army were the XXIV Corps and the III Amphibious Corps (IIIAC). The XXIV Corps comprised the Corps artillery and four infantry divisions: The 7th, 77th and 96th averaged around 22,000 personnel but were still 1,000 short as the replacement centres in the USA could not keep pace with both the war in Europe and the war in the Pacific. They were however reinforced by an engineer combat group, tank, amphibian tank, two amphibian tractor (amtracs) and two AAA battalions, as well as additional medical units.

US Marine Corps

The IIIAC consisted of: Unlike the Army divisions, the three Marine divisions went into the campaign at 100 percent strength and 2,500 replacements that were initially used as a shore party. This is thanks in part to the efficiency of the Marine Corps Replacement and Training Command, plus the fact that the Marine Corps only had six divisions to contend with and which were only fighting in the Pacific. The two corps (IIIAC and VAC) took it in turns to conduct operations so while VAC conducted Operation Detachment (Iwo Jima), IIIAC was already receiving and absorbing their replacements in preparation for Operation Iceberg (the assault on Okinawa). As IIIAC conducted Iceberg, the three VAC divisions (3rd, 4th and 5th) were busy being rebuilt for Operation Downfall (the invasion of Japan). The 1st, 2nd and 6th Marine Divisions also had a naval construction, an armoured amphibian tractor and two amphibian tractor battalions attached to them for Iceberg.

While there are some superficial similarities between the organisation of US Army and Marine Corps divisions, they are in reality quite different from one another. Neither of them can really be considered superior to the other as they both conducted amphibious operations, both fought the same enemy on the same terrain over the same period of time. Although the Marine division is specifically designed for such operations, the US Army division is easily tailored for the task. By 1945, Army divisions were somewhat smaller than Marine divisions in their basic size (14,000 vs. 19,000) but were better equipped in certain categories of weapons. Reinforced, the difference narrowed slightly as Army divisions grew to 22,000 and Marine divisions grew to 26,000 with supporting units.

Both divisions had four howitzer battalions, but whereas the Army had three 105mm-armed battalions and one 155mm-armed battalion, the Marines tended to have four 105mm-armed battalions, except the 1st Marine Division, whose 11th Marines had a battalion armed with 75mm pack howitzers. Marine divisions had a rocket detachment with 12 trucks mounting 4.5in Mk 7 launchers, whereas the Army had a rocket battalion. All howitzer battalions however had three batteries of four howitzers regardless of calibre.

The infantry regiments of both differed considerably although they used the same sort of equipment. Both the Army and the Marines used the 'triangular' structure - each regiment had three battalions, each of three rifle companies, each of three rifle platoons, each of three rifle squads. But it was there that any similarity ended. Army regimental strength was listed as 3,068 but on Okinawa started around 300 men below authorised strength. The regimental cannon company had six 105mm M7 self-propelled guns that made excellent assault guns for blasting caves and pillboxes, while the antitank company had nine 3.7cm M3A1 guns. The infantry battalion numbered some 860 personnel with a headquarters company and a heavy weapons company equipped with eight .30cal M1917A1 water-cooled machineguns and six 81mm M1 mortars. Each rifle company had some 193 personnel in three rifle platoons, each of three rifle squads, each with twelve men equipped with a Browning Automatic Rifle (BAR) M1918A2, eleven M1 Garand rifles and one M7 rifle grenade launcher. The company's weapons platoon had two .30cal M1919A4 air-cooled machineguns and three 60mm M2 mortars. A number of 2.36in M9 rocket launchers (bazookas) and M2-2 flamethrowers were also available.

The Army infantry regiment actually changed very little during the course of the Second World War, whereas the Marine infantry regiment (and indeed the division) underwent almost continuous evolution. By the time of Operation Iceberg, the divisions were still technically operating under the May 1944 Table of Organisation and Equipment (TO&E) but the regiments (each of 3,400 personnel) had reorganised under the 1 May 1945 TO&E that had been implemented early. The regimental weapons company consisted of two antitank platoons with four 3.7cm guns each and a self-propelled howitzer platoon of four 105mm M7s. The regimental headquarters included a scout and sniper platoon (43 men). There was no longer a separate weapons company in every infantry battalion (each of 996 men) - it had been disbanded and its weapons shared between the units that tended to make use of them. The battalion headquarters company had been given a mortar platoon with four 81mm mortars and an assault platoon (of fifty-five men) with three assault sections (each of two seven-man squads with a flamethrower, a 2.36in bazooka and demolition men) that would support each company. Each rifle company consisted of 242 men with three rifle platoons, a headquarters (fifty-one men) that had a section of three 60mm mortars and a machinegun platoon (forty-six men) that had eight .30cal air-cooled and six .30cal water-cooled machineguns. Each rifle platoon had 45 men in a headquarters and three thirteen-man rifle squads, each squad having a squad leader (M1 carbine), and three four-man fire teams with a team leader (M1 rifle, M7 grenade launcher), rifleman (M1 rifle), automatic rifleman (BAR) and assistant automatic rifleman (M1 rifle, M7 grenade launcher). The fire team concept had evolved from the Marine Corps involvement in the Banana Wars of the 1920s and 1930s with each team being built around an automatic weapon. It was a great success and eventually exported to many other armed forces.

Army companies were given a letter in sequence throughout the regiment, so the first battalion had companies A to D, the second battalion had E to H, the third battalion had I to M (no J) with D, H and M being heavy weapons. The regiment also had a headquarters (with reconnaissance and intelligence platoons) and a number of service companies that were unlettered. Marine companies were lettered in the same way as their Army counterparts but there were no D, H or M weapons companies (companies were not redesignated after the reorganisation, except in the 29th Marines). Both Army and Marine infantry regiments tended to be task organised into either Regimental Combat Teams (RCT) for the Army or Combat Teams (CT) for the Marines by attaching combat support and combat service support elements, such as engineer, pioneer, motor transport and medical units.

Medium tank battalions had seventeen M4A3 Sherman (75mm gun) tanks in each of the three companies (in three five-tank platoons and two in the headquarters) and three in the battalion headquarters for the Army, for a total of fifty-four tanks. The Marines on the other hand, had fifteen M4A2s (1st Battalion) or M4A3s (6th Battalion) in their three companies (four three-tank platoons and three in the headquarters) plus one in the battalion headquarters, for a total of forty-six tanks. The Army deployed the 713th Tank Battalion, which was equipped with flame-throwing tanks - the first if it's kind (Company B supported the Marines). The seven tank battalions would loose 153 tanks (51 Marine) to mines, antitank guns, artillery and suicide squads.

The six Army and five Marine amphibian tractor (amtrac) battalions all had three companies with 30 LVT(3) or LVT(4) each. The three Army amphibian tank and two Marine armoured amphibian tractor battalions each had four companies with eighteen LVT(A)(4) 75mm howitzer-armed amphibian tanks in each. They were deployed to provide armoured support to the assault troops until tanks could get ashore and after that act as self-propelled artillery.

Uniquely, the Tenth Army controlled a joint air command known as Tactical Air Force, Tenth Army (TG 99.2) that was activated on 21 November 1944 at Schofield Barracks, Hawaii. The 2nd Marine Air Wing (2nd MAW) doubled up as headquarters, TAF under Major General Francis P Mulcahy (who was relieved due to poor ehalth by Louis E Woods on 11 June 1945). Close air support (CAS) would initially be provided by Marine and Navy air units aboard the carriers of Task Force 51 but as airfields were captured, repaired and made useable, the TAF Marine and Army air units would move ashore. As its strength increased, TAF units would gradually assume greater responsibility for CAS, as well as photographic reconnaissance, resupply drops to the frontline, and protection from enemy air attacks including kamikazes. TAF was composed of four Marine Air Groups with fifteen fighter squadrons (three of which were equipped with night fighters) and two Marine torpedo bomber squadrons. It also had three US Army Air Force (USAAF - it wasn't until after the Second World War that it would become a separate branch of the armed services, the United States Air Force, USAF) fighter groups with ten fighter squadrons, one light (A26), two medium (B25) and two heavy (B24) bomber groups for a total of over 750 aircraft. Air support control units (Marine) accompanied both Army and Marine units ashore to direct CAS.


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Books (with Amazon.com & Amazon.co.uk)

Alexander, Joseph H. Storm Landings, Naval Institute Press, Annapolis, MD, 1997. A detailed account of the major amphibious assaults of the Pacific War. cover cover cover

Alexander, Col Joseph H. USMC (Ret). The Final Campaign: Marines in the Victory on Okinawa Marines in World War II Commemorative Series, Marine Corps Historical Centre, Washington DC, 1996. cover cover cover

Appleman, Roy E. Okinawa, Konecky & Konecky Military Books, 1994. cover cover cover

Astor, Gerald. Operation Iceberg, Dell Publishing, New York, 1998. cover cover cover

Iwo Jima and Okinawa , Black, Wallace B. , Prentice Hall, London, 1993 cover cover cover

Foster, Simon, Okinawa 1945 , Cassell Military, London, 1999. cover cover cover

Huber, Thomas M., Japan's Battle of Okinawa, April - June 1945 , Leavenworth Papers No. 18, Combat Studies Institute, US Army Command and Staff College, Fort Leavenworth, Kansas, 1990. cover cover cover

Leckie, Robert, Okinawa: The Last Battle of World War Two , Penguin Books, New York, 1996. cover cover cover

World War II , Matanle, Ivor, Godalming, 1995 (Second Edition). cover cover cover

Great Battles of World War II , Macdonald, John, Guild Publishing (BCA), London, 1986. cover cover cover

Rottman, Gordon L. Okinawa, 1945, Osprey Publishing, Oxford, 2002, Campaign Series No. 96. cover cover cover

Sledge, E B. With the Old Breed: At Peleliu and Okinawa, Naval Institute Press, Annapolis, MD, 1996 (Reprint). cover cover cover

Eagle Against The Sun, Spector, Ronald, Cassell Military, London, 2001. cover cover cover

cover The Pacific Campaign , Vat, Dan van der, Simon & Schuster, New York, 1991. cover cover cover

Wheeler, Richard. A Special Valor: The US Marines and the Pacific War, Harper & Row, 1983, New York. cover cover cover

A World at Arms : A Global History of World War II , Weinberg, Gerhard L, Cambridge University Press, 1994 cover cover cover

Yahara, Colonel Hiromichi. The Battle for Okinawa, John Wiley & Sons, London, 1997. cover cover cover

World War II , Young, Brigadier Peter. (Ed), Orbis Publishing, London, 1978. cover cover cover


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Photos courtesy of the Center for Military History, Fort Leslie J McNair, Washington DC.
How to cite this article: Antill, P. (2003), Operation Iceberg: The Assault on Okinawa - The Last Battle of World War II (Part 1) April - June 1945, http://www.historyofwar.org/articles/battles_okinawa1.html
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