Operation Iceberg: The Assault on Okinawa -
The Last Battle of World War II (Part 1)
April - June 1945
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?
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 (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).
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.
- 62nd Division - covered an area that ran north from Naha and Shuri in the south to a line that ran across the second narrowest point on the island, the Chatan Isthmus, that was some three-and-a-half miles across. Multiple defence lines stretch south from this point, just south of where the Americans would land, with a very formidable one centred on four kilometre-long Urasoe-Mura and Tanabaru Escarpments. The main defence line was further south still and centred on Shuri Castle as well as a vast cross-island ridgeline. The Americans would run into a well-prepared, in-depth defence line.
- 24th Division - covered the south of the island to prevent landings taking place there and act as the 32nd Army's reserve.
- 44th IMB - deployed southeast of the 62nd Division in the Chinen Peninsula in order to defend against any landing on the Minatogama Beaches.
- Okinawa Naval Base Force - deployed to secure the Oroku Peninsula southwest of the 62nd Division.
- 1st Specially Established Regiment - deployed to screen the two airfields on the central plains.
- 2nd Infantry Regiment - detached from the 44th IMB and deployed on the Motobu Peninsula, with one of its battalions on Ie Shima.
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.
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 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.
- 62nd Division - 14,000 veteran troops under Lt General Takeo Fujioka that had been activated in 1943 in the Sanshi Provinvce, China from the 4th and 6th IMBs, both of which were formed in 1938. The 62nd was a 'brigaded' division, consisting of the 63rd and 64th Infantry Brigades, each with four 1,080-man independent infantry battalions, each of which had five rifle companies, a machinegun company and an infantry gun company. In January 1945, both brigades acquired an additional 683-man independent infantry battalion that only had a machinegun company, three rifle companies and an infantry gun platoon. Finally it had 300-man engineer, signal and transport units and a field hospital but no organic artillery
- 24th Division - 15,000 well-trained soldiers under Lt General Tatsumi Amamiya had spent many years in Manchuria after being raised there in December 1939. It was a 'triangular' division with three 2,800-man regiments (22nd, 32nd and 89th) each with three battalions and an infantry gun company, while the battalions had six (three rifle, one machinegun, one antitank and one infantry gun) companies. The third battalion of each regiment had an 81mm mortar platoon instead of the infantry gun company. The 42nd Artillery Regiment had three battalions, the 1st and 2nd having one 75mm gun and two 100mm howitzer batteries, while the 3rd battalion had three 150mm howitzer batteries (each battery having four tubes). The division also had the 24th Reconnaissance Regiment (one machinegun and two rifle companies), 24th Engineer Regiment (three companies), 24th Transport Regiment (five companies - three motor and two horse) as well as 2 - 300-man signal, water supply and medical units.
- 44th Independent Mixed Brigade - had, to a large extent, be rebuilt once it had arrived on Okinawa but it never attained full strength and much of the 2nd Infantry Unit (1st and 2nd Battalions with gun and antitank companies) was posted to Okinawa's northern sector. It was under the command of Major General Suzuki Shigeki and consisted of the 2nd Infantry Unit (a regiment-sized formation) and the 15th Independent Mixed Regiment (that replaced the 1st Infantry Unit), both of three infantry battalions, one infantry gun company and one antitank company. The 700-man battalions had three rifle companies, one machinegun company and an infantry gun unit. The brigade also had a two-battery 75mm howitzer unit, a signal unit and an engineer company.
- 5th Artillery Group - included Imperial Japanese Navy (IJN) coastal defence gun companies and was under Major General Kosuki Wada that had fought at Bataan and had eight 150mm guns, thirty-six 150mm howitzers, eight 240mm howitzers, seventy-two 75mm cannons, ninety-six 81mm mortars and twenty-four of the new 320mm spigot mortars. The artillery units from the 24th Division and 44th IMB were also attached to this formation.
- 21st Antiaircraft Artillery Group - had four Antiaircraft Artillery (AAA) battalions with seventy-two 75mm AA guns, and three machinegun battalions with fifty-four 20mm cannons.
- 11th Shipping Group - operated IJN landing craft and later became a seaborne raiding force. In March it was formed into the 1st Specially Established Brigade consisting of the 2nd, 3rd and 4th Specially Established Regiments
- 27th Tank Regiment - consisted of thirteen Model 95 (1935) 37mm-armed Ha-Go light tanks and fourteen Model 97 (1937) 57mm-armed Chi-Ha medium tanks along with a rifle company. There were also three independent antitank battalions, each with eighteen of the excellent 47mm Model 1 guns and four independent heavy machine gun battalions.
- Other units - the Okinawa Naval Base Force (formed in April 1944) comprised some 10,000 sailors and marines under Rear Admiral Teiso Nippa that consisted of some fifteen coastal defence companies (120 and 140mm guns), four antiaircraft defence company groups (twenty 120mm, seventy-seven 25mm and sixty 13.2mm AA), Oroku Detachment, 951st Air Group, Nansei Shoto Air Group, 226th and 3210th Construction Units, a mortar battery (eighteen 81mm) and support personnel. There was also the 27th Torpedo Boat, 33rd Midget Submarine and 37th Torpedo Maintenance Units. In March, many of the service support personnel were formed into ad hoc 'specially established' rifle units that were attached to one of the two divisions or the 44th IMB. For example, the 1st Specially Established Brigade (formerly the 44th IMB) was attached to the 24th Division, while the 49th Line of Communications Sector was organised into the 2nd Specially Established Brigade (consisting of the 5th and 6th Specially Established Regiments) and attached to the 62nd Division, although the 6th Specially Established Regiment was transferred to the 44th IMB in late May. The 1st Especially Established Regiment was formed from the 19th Air Sector Command and also attached to the 62nd Division to help defend Kadena and Yontan airfields. The 1st, 2nd, 3rd and 26th Independent Battalions were created from the IJN sea raiding battalions in February. The final ad hoc unit was the 50th Specially Established Battalion on Ie Shima that was formed to screen flanks, man secondary lines and act as a pool of replacements. The Japanese often astounded the Americans with their ability to quickly organise units or reconstitute battered ones from survivors and ad hoc replacements during a battle, quite often using captured weapons.
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.
- 22nd Marines (6th Mar Div) - assigned to Green 1 and 2, would land with its 2nd and 3rd Battalions abreast with the 1st Battalion following.
- 4th Marines (6th Mar Div) - assigned to Red 1, 2 and 3, would land with its 3rd and 1st Battalions abreast, while its 2nd Battalion would be held as divisional reserve.
- 29th Marines (6th Mar Div) - would be held as IIIAC reserve to follow as necessary.
- 7th Marines (1st Mar Div) - assigned to Blue 1 and 2, would land with its 2nd and 1st Battalions abreast with the 3rd Battalion to follow.
- 5th Marines (1st Mar Div) - assigned to Yellow 1 and 2, would land with its 2nd and 1st Battalions abreast with its 3rd Battalion following.
- 1st Marines (1st Mar Div) - would be held as division reserve.
- 17th Infantry (7th Inf Div) - assigned to Purple 1 and 2, would land with its 3rd and 1st Battalions abreast with its 2nd Battalion following.
- 32nd Infantry (7th Inf Div) - assigned to Orange 1 and 2, would land with its 1st and 2nd Battalions abreast with its 3rd Battalion to follow.
- 184th Infantry (7th Inf Div) - would be held as divisional reserve.
- 381st Infantry (96th Inf Div) - assigned to White 1, 2 and 3, would land with its 3rd and 1st Battalions abreast with its 2nd Battalion following.
- 383rd Infantry (96th Inf Div) - assigned to Brown 1, 2, 3 and 4, would land with its 1st and 2nd Battalions abreast with its 3rd Battalion to follow.
- 382nd Infantry (96th Inf Div) - would be held as Corps reserve and land behind the 381st Infantry.
- Reserves - after conducting its feint, the 2nd Marine Division would remain as the Tenth Army Floating Reserve, the 27th Infantry Division would remain as the Expeditionary Troops Floating Reserve and the 81st Infantry Division would be kept on New Caledonia as the Area Reserve.
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.
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:
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:
- Task Force 58 (the Fast Carrier Force) - under Vice Admiral Marc A Mitscher that controlled some eighty-eight ships including eleven fleet carriers and six light carriers, almost 1,400 aircraft, seven battleships, eighteen cruisers, destroyers, frigates, minesweepers and a huge logistics support group.
- Task Force 57 (British Carrier Force) - under Vice Admiral Sir Bernard Rawlings controlled four carriers, two battleships, five cruisers and fourteen destroyers plus a fleet train. Many of its 260 aircraft were American built.
- Task Force 51 contained elements from the US Army, Marine and Navy, as well as their respective air arms and as such was a truly self-contained joint force capable of delivering itself to the area of operations, sustaining itself for 30 days, and conducting operations on land, in the air, as well as on and under the sea. It was made up of five smaller task forces and three task groups under Vice Admiral Richmond K Turner, Commander, Amphibious Forces, Pacific. These were: Task Force 52 (Amphibious Support Force) under Rear Admiral William H P Blandy with the eighteen escort carriers and 450 aircraft of Task Group 52.1 (Support Carrier Group), the four escort carriers that were to deliver Marine Aircraft Groups 31 and 33 ashore and sixty minesweepers of Task Group 52.2, as well as ten 100-man underwater demolition teams each on a destroyer transport (Task Group 52.11); Task Group 51.1 (Western Islands Attack Group) under Rear Admiral Ingolf N Kiland with the 77th Infantry Division tasked with securing Kerama Retto and other offshore islands prior to the landing and then Ie Shima; Task Force 53 (Northern Attack Group) under Rear Admiral Lawrence F Reifsnider with two transport groups containing the 1st and 6th Marine Divisions; Task Force 54 (Gunfire Support Force) under Rear Admiral Morton L Deyo with nine battleships, ten cruisers and a number of destroyers; Task Force 55 (Southern Attack Force) under Rear Admiral John L Hall with three transport groups containing the 7th, 27th and 96th Infantry Divisions; Task Group 51.2 (Demonstration Group) with a transport group containing the 2nd Marine Division; and Task Force 56 (Expeditionary Troops) that contained the remaining ground forces involved in the invasion, headquarters troops, as well as the follow-on occupation forces.
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.
The IIIAC consisted of:
- XXIV Artillery - under Brigadier General Josef R Sheetz and consisted of three artillery groups (419th Field, 420th Field and 144th Coast) with thirteen battalions with a mix of different calibres: 145th, 198th and 225th Field Artillery Battalions (155mm howitzer); 26th, 531st and 532nd Field Artillery Battalions (155mm gun); 287th Field Artillery Battalion (Observation); 421st Field Artillery Battalion (4.5in rocket); 749th and 750th Field Artillery Battalions (8in howitzer); and the 38th, 179th and 282nd Coastal Artillery Battalions (155mm gun).
- Corps Troops - this included the 1181st Engineer Construction Group, 521st Quartermaster Group and 71st Medical Battalion, as well as a variety of combat support battalions, including the 88th Chemical Mortar Battalion, 101st Signal Battalion and 519th Military Police Battalion, Army.
- 7th Infantry Division - commanded by Major General Archibald V Arnold, the 7th was a regular Army formation that had been reactivated on 1 July 1940 at Fort Ord, California, having previously served in World War One. It received desert training and then amphibious training from the Marines and then seized Attu Island in the Aleutians in May 1943. From there it moved to Hawaii and then assaulted Kwajalein Atoll in January 1944. After returning to Hawaii the division fought on Leyte in October and then prepared for Iceberg. It's constituent units were: 17th, 32nd and 184th Infantry Regiments; 48th, 49th, 57th (all 105mm) and 31st (155mm) Field Artillery Battalions; 13th Engineer Combat Battalion; 7th Reconnaissance Troop; and the 7th Medical Battalion.
- 96th Infantry Division - commanded by Major General James L Bradley, was an Army reserve formation that had been activated at the end of World War One but was not deployed overseas. It was reactivated on 15 August 1942 at Camp Adair, Oregon and after an extended period of training that included amphibious training with the Marines, it participated in the assault on Leyte in October 1944 after which it prepared for the assault on Okinawa. Its constituent units were: 381st, 382nd and 383rd Infantry Regiments; 361st, 362nd, 921st (all 105mm) and 363rd Field Artillery Battalions; 321st Engineer Combat Battalion; 96th Reconnaissance Troop; and the 321st Medical Battalion.
- 77th Infantry Division - under Major General Andrew B Bruce was, like the 96th, a reserve formation, but had actually seen combat in World War One. It was reactivated at Fort Jackson, South Carolina on 25 March 1942 and saw action on Guam under the command of the IIIAC in July 1944. It then saw action under the Sixth Army on Leyte from December 1944 to February 1945. It would in fact be the last division to land on Okinawa but the first to see combat in the Ryukyus, seizing the islands west of Okinawa. Its constituent units were: 305th, 306th and 307th Infantry Regiments; 304th, 305th, 902nd (all 105mm) and 306th (155mm) Field Artillery Battalions; 302nd Engineer Combat Battalion; 77th Reconnaissance Troop; and the 302nd Medical Battalion.
- 27th Infantry Division - under the command of Major General George W Griner was in fact the floating reserve and would land on Okinawa when necessary. It fielded just over 16,000 personnel and was some 2,000 infantry short. The 27th was a National Guard unit from New York, having served on the Mexican border in 1916 and fought in World War One. It was activated on 15 October 1940 in New York City and throughout its service, had a rather pained relationship with the Marines. After training in the southern United States, it moved to Hawaii and from there assaulted Saipan under the command of V Amphibious Corps (VAC). Its then commanding officer (Major General Ralph C Smith) was accused of excessive caution and a lack of aggression and therefore relieved of his command by the VAC commander (Lt General Holland M Smith), which soured Army - Marine relations. Its constituent units were: 105th, 106th and 165th Infantry Regiments; 104th, 105th, 249th (all 105mm) and 106th (155mm) Field Artillery Battalions; 102nd Engineer Combat Battalion; 27th Reconnaissance Troop; and the 102nd Medical Battalion.
- 81st Infantry Division - under the command of Major General Paul J Mueller was the Area Reserve and based on New Caledonia. It was not committed to action on Okinawa.
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.
- IIIAC Artillery - commanded by Brigadier General David R Nimmer and consisted of the 2nd Provisional Field Artillery Group of six battalions (the 2nd, 3rd and 6th, which were 155mm howitzer, and the 7th, 8th and 9th, which were 155mm gun, Field Artillery Battalions). These were arranged in two three-battalion groups to support the two Marine divisions once they were ashore. There was also the 1st Provisional Anti-Aircraft Artillery Group (2nd, 5th, 8th and 16th AAA Battalions), the 7th Service Regiment (initially deployed as the 7th Field Depot and then redesignated on 1 June 1945), one Army and one Marine engineer battalions and a four-battalion naval construction regiment.
- 1st Marine Division - contained a little over 26,000 personnel, under the command of Major General Pedro A del Valle. It has the nickname the 'Old Breed' and was formed from the 1st Marine Brigade (itself formed in 1935) at Guantánamo Bay, Cuba on 1 February 1941 and staged at Pavuvu for the invasion of Okinawa. It was the first American division committed to combat when it landed on Guadalcanal in August 1942 and fought on New Britain from December 1943 into 1944 and then assaulted Peleliu in September. There it encountered the new Japanese defensive tactics and use of cave defences and so that made it the best division for the Okinawa operation. It consisted of: the 1st, 5th, 7th (infantry) and 11th (artillery) Marines; 1st Tank Battalion; 1st Engineer Battalion; 1st Pioneer Battalion; 1st Motor Transport Battalion; 1st Service Battalion; and the 1st Medical Battalion.
- 6th Marine Division - contained just over 24,000 personnel and was commanded by Major General Lemuel C Shepherd. It was the newest of the Marine divisions but seven out of the nine infantry battalions had combat experience. The division was formed on the 7 September 1944 at Tassafarongo, Guadalcanal from the units of the 1st Provisional Marine Brigade that had fought on Guam in July, as well as the 4th and 22nd Marines. The 4th Marines was made up from former Raider battalions that had been at Midway, Guadalcanal, Makin, Pavuvu, New Georgia and Bougainville. It had secured Eniwetok and Guam as well as islands in the Marshalls. The 1st Battalion, 29th Marines had fought on Saipan and Tinian (these, along with Guam, formed the Mariana Islands) and were joined by the rest of the 29th Marines to form the division. It consisted of: the 4th, 22nd, 29th (infantry) and 15th (artillery) Marines; 6th Tank Battalion; 6th Engineer Battalion; 6th Pioneer Battalion; 6th Motor Transport Battalion; 6th Service Battalion; and the 6th Medical Battalion.
- 2nd Marine Division - contained a little over 22,000 personnel under the command of Major General Thomas E Watson. The division was created from the 2nd Marine Brigade stationed at San Diego on the 1 February 1941. The brigade had previously fought in China. The majority of the division had fought on Guadalcanal in 1942 - 3 and then assaulted the Tarawa Atoll (specifically, Betio Island) in November 1943. It then fought on Saipan and Tinian in mid-1944 (the Marianas campaign) and served as a demonstration force off Okinawa, stayed for a while as a floating reserve and finally left for Saipan as an Area Reserve. The 8th Marines (Reinforced) later returned as a Special Landing Force to secure the offshore islands in June and was then attached to the 1st Marine Division for the remainder of the battle. It consisted of: the 2nd, 6th, 8th (infantry) and 10th (artillery) Marines; 2nd Tank Battalion; 2nd Engineer Battalion; 2nd Pioneer Battalion; 2nd Motor Service Battalion; 2nd Service Battalion; and the 2nd Medical Battalion.
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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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