Operation Campaign for Okinawa

The 'Campaign for Okinawa' was fought by invading US and defending Japanese forces for the possession of the island of Okinawa to the south of the other four Japanese home islands (1 April/22 June 1945).

Codenamed 'Iceberg', this was a major element of the Pacific War fought by formations of the US Army and US Marine Corps against Japanese formations in the final major land campaign of World War II in the Pacific. The invasion of Okinawa on 1 April 1945 was the largest amphibious assault in the Pacific theatre.

The small islands of the Kerama group to the west of southern Okinawa were captured as a pre-emptive move on 26 March by the 77th Division, and the battle for the altogether larger islands of Okinawa proper then lasted 82 days from 1 April to 22 June. After a long campaign of island hopping, the Allies were planning to use Kadena air base as a major support for 'Downfall', the planned invasion of the Japanese home islands some 340 miles (550 km) distant to the north-east.

The USA created the 10th Army, a cross-branch force comprising the US Army’s 7th, 27th, 77th and 96th Divisions and the US Marine Corps' 1st, 2nd and 6th Marine Divisions, to fight on the island. The 10th Army was unique in that it had its own tactical air force (a joint army and marine command), and was also supported by combined naval and amphibious forces. Opposing the Allied forces on the ground was the Japanese 32nd Army.

The battle has been referenced in English as the 'typhoon of steel', and in Japanese as the kotetsu no ame (rain of steel) and kotetsu no hageshi kaze (violent wind of steel). The nicknames reflect the ferocity of the fighting, the intensity of Japanese kamikaze attacks and the sheer numbers of Allied ships and armoured vehicles which descended on the island. The battle was the bloodiest of the Pacific War, with an overall total of some 160,000 military casualties: at least 50,000 Allied and between 84,166 and 117,000 Japanese including drafted Okinawans wearing Japanese uniforms. According to local authorities, at least 149,425 Okinawan people died, either by suicide or mere disappearance, which represents approximately half of the island’s estimated pre-war population of about 300,000 persons.

In the naval operations surrounding the battle, both sides lost considerable numbers of aircraft and ships, the latter including the Japanese super-battleship Yamato. After the battle, Okinawa provided the US forces with a fleet anchorage, troop staging areas, and airfields in proximity to Japan in preparation for the planned invasion of the Japanese home islands.

The Okinawa gunto (islands group) is the largest in the Ryukyu retto (islands chain) extending to the south-west from Kyushu, and is about 320 miles (515 km) from Kyushu. Okinawa itself, which had an area of 463 sq miles (1199 km), is the fifth of what the Japanese deem their home islands, and is by far the smallest of the home islands. It lies 350 miles (565 km) to the north-east of Formosa and 460 miles (740 km) to the east of the Chinese mainland. Manila in the Philippine islands group is 790 miles (1270 km) to the south-west, Guam is 1,230 miles (1980 km) to the south-east, and Pearl Harbor is 4,040 miles (6500 km) to the east. While the island was not intrinsically important in World War II, the fact that it is located 450 miles (725 km) to the south-east of Shanghai in China and 540 miles (870 km) to the south-south-east of Pusan in Korea later came to increase its strategic importance. Clustered round Okinawa are several other islands and small groups of islands comprising the Okinawa gunto: the Kerama retto of eight islands 15 miles (24 km) to the west of Okinawa, Kume Shima 55 miles (88.5 km) tro the west, Agunia Shima 40 miles (65 km) to the west), Ie Shima 4 miles (6.4 km) to the west, the Iheya retto of four islands 15 miles (24 km) to the north, Yoron Shima 15 miles (24 km) to the north-east, and an unnamed group of eight scattered islands in the Kin Wan 5 to 10 miles (8 to 16 km) to the east. Most of these islands came to play important roles in the Okinawa campaign.

Japan had gained partial control of the islands in the 1500s and in 1609, after Okinawa had refused to provide troops for Japan’s war against Korea, Japan invaded and devastated the island kingdom. Okinawa nonetheless maintained a semi-independent status paying tribute to both Japan and China. Commodore Matthew Perry used Okinawa as a supply base during his 1853 effort to establish trade with Japan, raising the US flag on a hill near Shuri Castle. The opening of Japan to the rest of the world quickly established the country as a regional power and it took control of Okinawa in 1867. The Ryukyuan king was given a permanent residence in Tokyo and in 1874 the Japanese home ministry took total control of the islands. A Japanese governor was installed in 1879 and the islands were given prefecture status. China still claimed the islands and the Okinawans preferred their fence-sitting status between the two powers, but they were now solidly part of the Japanese empire. Okinawa was granted a prefecture assembly and a seat in the Diet (parliament) in 1920. In 1943, the prefecture of Okinawa was consolidated with seven others into the Home Islands District of Kyushu.

Okinawa Shima is oriented north-east/south-west and has a length of 64 miles (103 km) with a width varying between 18 miles (29 km) at the Motobu peninsula extending to the east from the island’s northern portion to a mere 2 miles (3.2 km) at the Ishikawa isthmus just to the south of the island’s middle. Several smaller peninsulas jut from the island’s southern portion and provide for excellent anchorages.

The Ishikawa isthmus separates Okinawa into two contrasting regions. The sparsely populated north is covered with rugged, ridge-like hills between 1,000 and 1,500 ft (305 and 460 m) high branching off a central ridge. The areas round the hills are cut by deep ravines and gullies terminating at the coast in steep cliffs. On the north-western coast, the Motobu peninsula is a dominant feature and became the centre of Japanese resistance in the north. The entire area is covered by dense forests of pine, live oak and thick underbrush. The road system was extremely limited, with a only a single one-lane road following the north-western coast to the island’s northern end. Cross-country vehicle movement is impossible. The soil is red clay and sandy loam and well drained by the many small streams. This region stretches to the south past the Ishikawa isthmus to the island’s southern one-third.

The heavily populated south is characterised by rolling hills, sometimes terraced, gradually reaching to a height of more than 500 ft (150 m) at the island’s southern end. The hills are cut by ravines and shallow, narrow streams providing poor drainage. The farther south one goes, the more hilly and broken the terrain becomes. Caves, cut by underground streams, honeycomb the hills and ridges. The central plains to the south of the Ishikawa isthmus are open and gently rolling. Farther to the south the terrain is dotted with small scattered, irregular knolls, and these were incorporated into the Japanese defensive arrangements. The hills are steep in some areas and several escarpments and twisting limestone ridges cut across the island providing successive cross-compartment defensive lines as one moves to the south. Few long fields of fire exist, and this was of benefit to the Japanese short-range weapons.

While some areas were lightly wooded, four-fifths of the south was cultivated with sweet potato, sugar cane, rice, and soya bean fields in the valleys and on hills and plateaus. Fishing was secondary to farming as the island’s principal industries. Villages and towns were scattered across the southern region and connected by a network of single-lane roads and trails. Some of these were surfaced with crushed coral, but most were earthen cart tracks. A single two-lane limestone road connected the island’s only two towns, Naha and Shuri. Because of the clay soil conditions, the largely unimproved roads were totally incapable of supporting military traffic during the rainy season. Off-road traffic was impossible in most areas when the rains came. A narrow-gauge railway connected Naha, Kobakura, Kobuba and Yonabaru, with branches linking Kobakura to Kadena and Kokuba with Itoman. The 30 miles (48 km) of track were used primarily for the movement of produce, and some were later returned to service by US engineers.

Much of the coast is fronted by limestone cliffs and scattered coral heads. The most desirable landing beaches were those at Hagushi on the west coast in the area to the south of the 2-mile (3.2-km) wide Ishikawa isthmus and edging the central plains. The beaches were named after the centrally located Hagushi village at the mouth of the Bishi Gawa (stream). Hagushi, however, was actually a mistranslation, for the village’s real name was Togushi. The Japanese called them the Kadena beaches. The usual coral reef shelf paralleled the shore with a higher seaward crest between 200 and 700 yards (180 and 650 m) offshore and then deepened closer to the shore. At low tide trucks could be driven across it. The area’s mean tides are 4 ft (1.2 m), but at the time of the US landings a spring tide raised the water level to 6 ft (1.8 m). The 8 miles (12.8 km) of landing beaches were gently sloping with few natural obstacles, although there were extensive sea walls up to 10 ft (3.05 m) high. The beaches were not continuous, but separated into 100- and 900-yard (90- and 825-m) lengths by low-cliff headlands. At low tide the beaches were 10 to 45 yards (3.05 to 41 m) eide, but at high water were completely awash. Behind the beaches sparsely vegetated and cultivated ground rose gradually to a height of 50 ft (15.25 m). The beaches were selected because of their proximity to Yontan and Kadena airfields some 2,000 yards (1840 m) inland as their early seizure would allow land-based fighters to fly close air support and aid in the defence of the fleet.

The population of Okinawa was 435,000 and included thousands of Japanese immigrants serving as government officials, administrators, managers and merchants. Naha is Okinawa’s prefectural capital and commercial centre with a pre-invasion population of more than 60,000 persons, and was the island’s main port. Shuri was slightly smaller and was the Ryukyu islands group’s traditional capital. Shuri Castle is perched on the massive ridge cutting across the island and was the ancient seat of the Ryukyuan kings, and was to become a vicious battleground. On the eastern side of the island’s southern portion is the broad Nakagusuku bay, which was considered as a landing site.

Most of the island’s population lived in villages ranging from fewer than 100 persons up to 1,000 or more persons. The towns of Itoman, Nago and Yonabaru were simply large villages with few modern buildings. Concrete and stone government and commercial buildings were numerous in Naha and Shuri, but most urban buildings and dwellings were single-storey structures of wood surrounded by low stone walls. Houses in the villages had clay walls and thatched roofs, and were surrounded by bamboo windbreaks or low stone or mud walls overgrown with tropical vegetation. Unique to Okinawa were the lyre-shaped stone family tombs, an important part of the indigenous animistic cult emphasizing the veneration of ancestors. Dug into hillsides, they did not provide all-around defence, but did offer protection from artillery fire and their vulnerable sides could be covered from other fighting positions.

The Imperial Japanese army’s two main airfields, Yontan and Kadena, were sited on the central plains, while Mach-chiano airfield was located just to the north of Naha. Across from it on the eastern coast was the abandoned Yonabaru airfield. An Imperial Japanese navy airfield was located on the Oroku peninsula. Two airfields were located on Ie Shima.

Before the invasion, 80,000 Okinawans had been shipped to Kyushu, to work in factories, aboard returning supply ships, of which some were sunk en route by US submarines. Another 60,000 Okinawans were forced to relocate to the sparse north as a means of reducing the burden on Japanese forces in the heavily populated south.

Okinawa’s temperatures are moderate, with a winter night low of 4.4 C (40 F), but at the time of the battle day temperatures were in the range between 21 C (70 F) and 27 C (80F) or more. Humidity is high right through the year, and rain is frequent but irregular, with the heaviest occurring from May to September during the summer monsoon. Rain was to have a major impact on the 'Campaign for Okinawa'. Moderate winds varied from south to east at the time of the battle.

For 'Iceberg', Lieutenant General Simon B. Buckner’s US 10th Army had more than 103,000 men, of whom more than 38,000 were non-divisional artillery, combat support and headquarters troops, and another 9,000 were service troops, more than 88,000 men of the US Marine Corps and 18,000 US Navy personnel, of whom most were 'Seabee' construction troops and medical personnel. At the start of the 'Campaign for Okinawa', therefore, the 10th Army had 182,821 personnel.  It was planned that Buckner would report to Vice Admiral Richmond K. Turner until the amphibious phase had been completed, after which he would report directly to Admiral Raymond A. Spruance. The total number aircraft in the US Navy, US Marine and US Army Air Force formations exceeded 3,000 over the course of the battle, and types included fighters, fighter-bombers, attack aircraft, reconnaissance and scout aircraft, bombers and dive-bombers. The invasion was supported by a fleet comprising 18 battleships, 27 cruisers, 177 destroyers and destroyer escorts, 39 aircraft carriers (11 fleet carriers, six light carriers and 22 escort carriers) and various support and troop transport ships.

The British naval contingent accommodated 251 British naval aircraft, and included a British and commonwealth fleet with Australian, New Zealand and Canadian ships and personnel.

The Northern Landing Beaches were the responsibility of the US Marine Corps' III Amphibious Corps under the command of Major General Roy S. Geiger. Within these, the Left Beaches were allocated to Major General Lemuel C. Shepherd’s 6th Marine Division of 24,356 officers and men, which was to land two battalions of Colonel Merlin F. Schneider’s 22nd Marine Regiment on the two Beaches Green, and two battalions of Colonel Alan Shapley’s 4th Marine Regiment on the three Beaches Red; while the Right Beaches were the responsibility of Major General Pedro A. del Valle’s 1st Marine Division of 26,274 officers and men, which was to land two battalions of Colonel Edward W. Snedeker’s 7th Marine Regiment on the two Beaches Blue, and two battalions of Colonel Arthur T. Mason’s 1st Marine Regiment on the three Beaches Yellow. Each regiment had its third battalion in reserve, and was supported by one marine artillery regiment. Anti-aircraft firepower was provided by Colonel Kenneth W. Benner’s 1st Provisional Anti-Aircraft Artillery Group.

The Southern Landing beaches were the responsibility of the US Army’s XXIV Corps under the command of Major General John R. Hodges. The Left Beaches were to receive the landings of Major General Archibald V. Arnold’s 7th Division of 21,929 officers and men, which was to land two battalions of the 17th Infantry on the two Beaches Purple and two battalions of the 32nd Infantry on the three Beaches Orange, while the Right Beaches were to receive the landings Major General James L. Bradley’s 96th Division of 12,330 officers and men, which was to landed two battalions of the 381st Infantry on the three Beaches White and two battalions of the 383rd Infantry on the four Beaches Brown. Each regiment had its third battalion in reserve and was supported by the 105-mm (4.13-in) guns of three field artillery battalions and the 155-mm (6.1-in) guns of one field artillery battalion, the divisional reserve was the 184th Infantry, and the corps' reserve was Major General George W. Griner’s 27th Division of 16,143 officers and men, which had the support of three battalions of 105-mm (4.13-in) guns and one battalion of 155-mm (6.1-in) guns.

The assault on the western islands was entrusted to Major General Andrew D. Bruce’s 77th Division, whose 20,981 officers and men provided the strength of three infantry regiments (306th Infantry on Beach Green, 305th Infantry on Beaches Red 1 and 2, and 307th Infantry on Beaches Red 3 and 4). Each regiment had three battalions of 105-mm (4.13-in) guns and one battalion of 155-mm (6.1-in) guns.

The Tactical Air Force, 10th Army, was commanded by a marine officer, Major General Francis P. Mulcahy.

The Japanese campaign on Okinawa was undertaken by the 67,000- to 70,000-man 32nd Army of the Imperial Japanese army and some 9,000 Imperial Japanese navy troops at the Oroku base (of whom only a few hundred were trained and equipped for ground combat), supported by 39,000 drafted local Ryukyuan people (including 24,000 hastily drafted rear militia called Boeitai and 15,000 non-uniformed labourers. The Japanese had used kamikaze tactics since the 'Battle of Leyte Gulf', but for the first time these became a major part of the defence. Between the US landings on 1 April and 25 May, seven major kamikaze attacks were attempted, these involving more than 1,500 aircraft.

Under the command of Lieutenant General Mitsuru Ushijma, the 32nd Army initially comprised the 9th Division, Lieutenant General Tatsumi Amamiya’s 24th Division of three infantry regiments, Lieutenant General Takeo Fujioka’s 62nd Division of two brigades, and Major General Suzuki Shigeji’s 44th Independent Mixed Brigade. The 9th Division was removed to Formosa before the US invasion, resulting in shuffling of Japanese defensive plans. Primary resistance was to be led in the south by Ushijima, his chief-of-staff, Lieutenant General Isamu Cho, and his chief of operations, Colonel Hiromichi Yahara. Yahara and Cho advocated a defensive and an offensive strategy respectively. In the north, Colonel Takehido Udo was in command. The naval forces were led by Rear Admiral Minoru Ota. The Japanese expected the Americans to land between six and 10 divisions against the Japanese garrison of 2.5 divisions. The staff calculated that superior quality and numbers of weapons gave each US division five or six times the firepower of a Japanese division. To this, would be added the US forces' abundant naval and air firepower.

On Okinawa, the Imperial Japanese army conscripted 780 schoolboys aged between 14 and 17 years into front-line service as a Tekketsu Kinnotai (Iron and Blood Imperial Corps). while Himeyuri (high school girls) were organised into a nursing unit. This mobilisation was ordained by the army ministry rather than by law. For form’s sale, the ordinances mobilised the students as 'volunteer soldiers', but in reality the military authorities ordered schools to force almost all students to 'volunteer'. About half of the Tekketsu Kinnotai were killed, some of them in suicide bomb attacks against tanks, and in guerrilla operations. Among the 21 male and female secondary schools which contributed to these student corps, 2,000 students died on the battlefield. Even serving mainly as nurses, the female students were still exposed to the harsh conditions of war.

The US Navy’s Task Force 58 (Fast Carrier Task Force), commanded by Vice Admiral Marc A. Mitscher and deployed to the east of Okinawa with a picket group of six to eight destroyers, kept 13 aircraft carriers (seven fleet carriers and six light carrier) on duty from 23 March to 27 April, and a smaller number after that time. Until 27 April, a minimum of 14 and up to 18 escort carriers were in the area at all times. Until 20 April, Vice Admiral Sir Bernard Rawlings’s British TF57, with four fleet and six escort carriers, remained off the Sakishima islands group to protect the southern flank. 

The protracted length of the campaign under stressful conditions forced Admiral Chester W. Nimitz, commander-in-chief of the Pacific Fleet and the Pacific Ocean Areas, to take the unprecedented step of relieving the principal naval commanders to rest and recuperate. Following the practice of changing the fleet designation with the change of commanders, US naval forces began the campaign as the US 5th Fleet under the command of Admiral Raymond A. Spruance but ended it as the US 3rd Fleet under the command of Admiral William F. Halsey.

Japanese air opposition had been relatively light during the first few days after the landings. However, on 6 April, the expected air reaction began with an attack by 400 aircraft from Kyushu, and periodic heavy air attacks continued throughout April. During the period between 26 March and 30 April, 20 US ships were sunk and 157 damaged by Japanese action, while the Japanese had, by 30 April, lost more than 1,100 aircraft to the Allied naval forces alone.

Between 6 April and 22 June, the Japanese flew 1,465 kamikaze aircraft in large-scale attacks from Kyushu, 185 individual kamikaze sorties from Kyushu, and 250 individual kamikaze sorties from Formosa. While US intelligence had estimated that there were only 89 aircraft on Formosa, the Japanese actually had about 700, dismantled or well camouflaged and dispersed into scattered villages and towns. The US 5th Army Air Force disputed US Navy claims of kamikaze operating from Formosa.

The ships lost were smaller vessels, particularly the destroyers of the radar pickets, as well as destroyer escorts and landing ships. While no major Allied warships were lost, several fleet carriers were severely damaged. Land-based 'Shinyo' class suicide motor boats were also used in the Japanese suicide attacks, although Ushijima had disbanded the majority of the suicide boat battalions before the battle as he believed that they would not be effective against a superior opponent. The boat crews were re-formed into three additional infantry battalions.

The Japanese 'Ten' operation was an attempted attack by a force of 10 Japanese surface vessels, led by the super-battleship Yamato and commanded by Vice Admiral Seiichi Ito. This small task force had been ordered to fight through the US naval forces round Okinawa, then beach Yamato to fight from the shore, using her 460-mm (18.1-in) main guns as coastal artillery and her crew as naval infantry. The 'Ten' force was spotted by US submarines shortly after it left Japanese home waters, and was intercepted by US carrier aircraft. Under attack from more than 300 aircraft over a two-hour period, the world’s largest battleship was sunk on 7 April after a one-sided battle, long before she could reach Okinawa. (US torpedo bombers were instructed to aim only for one side to prevent effective counter-flooding by the battleship’s crew, and to aim for the bow or the stern, where the battleship’s armour was known to be the thinnest.) Of Yamato's screening force, the light cruiser Yahagi and four of the eight destroyers were also sunk. The Imperial Japanese navy lost some 3,700 sailors, including Ito, at the cost of 10 US aircraft and 12 airmen.

The British Pacific Fleet, under the overall command of Admiral Sir Bruce Fraser and taking part as Rawlings’s TF57, was assigned the task of neutralising the Japanese airfields in the Sakishima islands group, which it achieved from 26 March to 10 April. On this latter date, TF57 switched its attention to airfields in the northern part of Formosa. The force withdrew to San Pedro Bay on 23 April. On 1 May, TF57 returned to action, subduing the airfields as before, this time with naval bombardment as well as aircraft. Several kamikaze attacks caused significant damage, but as the Royal Navy carriers had armoured flight decks, they experienced only a brief interruption to their force’s operations.

The land battle on Okinawa and its surrounding islands lasted some 82 days beginning on 1 April. The first US troops to come ashore were men of the 77th Division, who landed in the Kerama islands group, 15 miles (24 km) to the west of Okinawa on 26 March. Other subsidiary landings followed, and the Kerama islands group was secured over the next five days. In these preliminary operations, the 77th Division suffered 27 men killed and 81 wounded, while the Japanese dead and captured numbered more than 650. The operation provided a protected anchorage for the fleet and eliminated the threat from suicide boats.

On 31 March, marines of the Amphibious Reconnaissance Battalion landed without opposition on Keise Shima, a group of four islets just 8 miles (13 km) to the west of the Okinawan capital of Naha. A group of 155-mm (6.1-in) guns was landed on these little islands to provide cover for operations on Okinawa.

The main landings on Okinawa proper were made on 1 April by Hodge’s US Army XXIV Corps (Southern Landing Beaches) and Geiger’s US Marine Corps III Amphibious Corps (Northern Landing Beaches) on the Hagushi beaches on the western coast of Okinawa. The two corps were the primary formations for the amphibious Phase I of 'Iceberg' under the command of Vice Admiral Richmond K. Turner’s Joint Expeditionary Task Force (TF51). The 2nd Marine Division made a demonstration off the Minatoga beaches on the island’s south-eastern coast to deceive the Japanese about US intentions and thereby delay the Japanese movement of reserves from that region.

The 10th Army swept across the south-central part of Okinawa with relative ease, capturing the Kadena and the Yomitan air bases within hours of the landing. In light of the weak opposition, Buckner then decided to proceed immediately with Phase II of his plan, the seizure of northern Okinawa. The 6th Marine Division advanced up the Ishikawa isthmus and, by 7 April, had isolated the Motobu peninsula. Six days later, on 13 April, the 2/22nd Marines reached Hedo Point at the northernmost tip of the island. By this point, the bulk of the Japanese 'Udo' Force in the north was trapped on the Motobu peninsula. Here, the terrain is mountainous and wooded, and the Japanese defences were concentrated on Yae-Dake, a twisted mass of rocky ridges and ravines in the middle of the peninsula. There was heavy fighting before the marines finally cleared Yae-Dake on 18 April. This was not the end of ground combat in northern Okinawa, however, for on 24 May the Japanese mounted their 'Gi' (iii) operation in which one company of Giretsu Kuteitai commandos was airlifted in a suicide attack on Yomitan air base. The commandos destroyed 70,000 US gal (260000 litres) of fuel and nine aircraft before being killed by the defenders, who lost two men.

Meanwhile, the 77th Division assaulted Ie Shima, a small island off the western end of the peninsula, on 16 April. In addition to conventional hazards, the 77th Division encountered kamikaze attacks and even local women armed with spears. There was heavy fighting before the area was declared secure on 21 April to become another air base for operations against Japan.

While the 6th Marine Division cleared the northern part of Okinawa, the US Army’s 96th Division and 7th Division wheeled to the south across the narrow waist of Okinawa. The 96th Division began to encounter fierce resistance in west-central Okinawa from Japanese troops holding fortified positions to the east of Highway 1 and about 5 miles (8 km) to the north-west of Shuri, from what came to be known as 'Cactus Ridge'. The 7th Division encountered similarly fierce Japanese opposition from a rocky pinnacle, later dubbed 'The Pinnacle' located about 1,000 yards (915 m) to the south-west of Arakachi. By the night of 8 April, US troops had cleared these and several other strongly fortified positions. They suffered more than 1,500 battle casualties in the process while killing or capturing about 4,500 Japanese. Yet the battle had only just begun, for it was now realised that 'these were merely outposts' guarding the Shuri Line.

The next US objective was Kakazu Ridge, which was a pair of hills with a connecting saddle that formed part of Shuri’s outer defences. The Japanese had prepared their positions well and fought tenaciously from fortified caves. The US forces often lost personnel before clearing the Japanese from each cave or other hiding place. The Japanese sent Okinawans at gunpoint out to obtain water and supplies for them, which led to civilian casualties. Yet the US advance was inexorable, but resulted in a high number of casualties on each side.

As the US assault on Kakazu Ridge stalled, Ushijima succumbed to pressure from Cho and decided to take the offensive. On the evening of 12 April, the 32nd Army attacked US positions across the entire front. The Japanese attack was heavy, sustained and well organised, but after fierce close combat, the attackers retreated, only to repeat their offensive in the course of the following night. A final assault on 14 April was again repulsed. The effort led the staff of the 32nd Army to the conclusion that while the US forces were vulnerable to night infiltration tactics, their superior firepower made any offensive Japanese troop concentrations extremely vulnerable, so they reverted to their defensive strategy.

Griner’s 27th Division, which had landed on 9 April, took over on the right, along the western coast of Okinawa. Hodge now had three divisions in the line, with the 96th Division in the middle and the 7th Division to the east, each division holding a front of only about 1.5 miles (2.4 km). Hodge launched a new offensive on 19 April with a barrage by 324 pieces of artillery, the largest ever in the Pacific Ocean theatre. Battleships, cruisers and destroyers joined the bombardment, which was followed by 650 US Navy and US Marine Corps aircraft attacking the Japanese positions with napalm, rockets, bombs, and machine guns. The Japanese defences were sited on reverse slopes, where the defenders waited out the artillery barrage and aerial attack in relative safety, emerging from their caves to rain mortar bombs and grenades on the US troops advancing up the forward slope.

A tank assault to achieve a breakthrough by outflanking Kakazu Ridge failed to link with its infantry support attempting to cross the ridge and therefore failed with the loss of 22 tanks. Although flamethrower tanks cleared many cave defences, there was no breakthrough, and the XXIV Corps suffered 720 casualties. The losses might have been greater except for the fact that the Japanese had practically all of their infantry reserves committed farther to the south, held there by another feint off the Minatoga beaches by the 2nd Marine Division.

At the end of April, after US Army forces had pushed through the Machinato defensive line, the 1st Marine Division relieved the 27th Division and the 77th Division relieved the 96th Division. When the 6th Marine Division arrived, the III Amphibious Corps took over the right flank and the 10th Army assumed control of the battle.

On 4 May, the 32nd Army launched another counter-offensive. This time, Ushijima attempted to make amphibious assaults on the coasts behind the US lines. To support his offensive, the Japanese artillery moved into the open: by doing so, it were able to fire 13,000 rounds in support, but effective US counter-battery fire destroyed dozens of Japanese pieces of artillery. The counter-offensive thus failed.

Buckner launched another US attack on 11 May, and there followed 10 days of fierce fighting. On 13 May, men of the 96th Division and the 763rd Tank Battalion captured 'Conical Hill'. Rising 476 ft (145 m) above the Yonabaru coastal plain, this feature was the eastern anchor of the main Japanese defences and was defended by about 1,000 Japanese. Meanwhile, on the opposite coast, the 1st Marine Division and 6th Marine Division fought for 'Sugar Loaf Hill'. The capture of these two key positions exposed the Japanese around Shuri on both flanks. Buckner hoped to envelop Shuri and trap the main Japanese defending force.

By the end of May, monsoon rain, which had turned contested hills and roads into a morass, worsened both the tactical and medical situations. The ground advance began to resemble that on a World War I battlefield as men became mired in mud, and flooded roads greatly inhibited evacuation of wounded to the rear. Troops lived on ground sodden by rain, part garbage dump and part graveyard. Unburied Japanese and US bodies decayed, sank in the mud and became part of a noxious stew. Anyone sliding down the greasy slopes often found his pockets full of maggots at the end of the journey.

From 24 to 27 May the 6th Marine Division cautiously occupied the ruins of Naha, the largest city on the island, finding it largely deserted.

On 26 May air reconnaissance saw large troop movements just below Shuri. On 28 May marine patrols found recently abandoned positions to the west of Shuri. By 30 May the consensus among US Army and US Marine Corps intelligence teams was that the majority of Japanese forces had withdrawn from the Shuri Line. On 29 May the 1/5th Marines occupied high ground 700 yards (640 m) to the east of Shuri Castle and reported that the castle appeared undefended. At 10.15 Company A of the 1/5th Marines occupied the castle, now nothing but a ruin.

Shuri Castle had been shelled by the battleship Mississippi for three days before this advance, and as a result the 32nd Army had withdrawn to the south and thus the marines had an easy task in securing the castle. This lay outside the 1st Marine Division’s assigned zone, however, and only frantic efforts by the commander and staff of the 77th Division prevented a US air attack and artillery bombardment which would have resulted in many 'friendly fire' casualties.

Although harassed by US artillery fire, the Japanese retreat had been undertaken at night with great skill under cover of the monsoon storms. The 32nd Army was able to move nearly 30,000 personnel into its last defence line on the Kiyan peninsula, which ultimately led to the greatest slaughter on Okinawa in the latter stages of the battle, including the deaths of thousands of civilians. In addition, there were 9,000 Imperial Japanese navy troops supported by 1,100 militia, with about 4,000 persons holed up at the underground headquarters on the hillside overlooking the Okinawa naval base on the Oroku peninsula, to the east of the airfield. On 4 June, elements of the 6th Marine Division launched an amphibious assault on the peninsula. On 13 June, the 4,000 Japanese sailors, including Minoru Ota, all committed suicide within the hand-built tunnels of the underground naval headquarters.

By 17 June, the remnants of the 32nd Army had been driven into a small pocket in the far south of the island in the area to the south-east of Itoman.

On 18 June, Buckner was killed by Japanese artillery fire while monitoring the progress of his troops from a forward observation post. Buckner was replaced on a temporary basis by Geiger who, on assuming command, became the only US Marine to command a numbered army of the US Army in combat. Geiger was relieved five days later by Lieutenant General Joseph W. Stilwell. On 19 June, Brigadier General Claudius M. Easley, assistant commander of the 96th Division, was killed by Japanese machine gun fire as he supervised the progress of his troops at the front.

The last remnants of Japanese resistance ended on 21 June, although some Japanese continued hiding. Ushijima and Cho committed suicide in their command headquarters on Hill 89 in the closing hours of the battle.  Colonel Yahara had asked Ushijima for permission to commit suicide, but the general refused his request, saying that 'If you die there will be no one left who knows the truth about the battle of Okinawa. Bear the temporary shame but endure it. This is an order from your army commander.' Yahara was the most senior officer to survive the battle on the island. On 22 June the 10th Army held a flag-raising ceremony to mark the end of organised resistance on Okinawa. On 23 June a mopping-up operation began, and this ended on 30 June.

On 15 August, Admiral Matome Ugaki was killed while part of a kamikaze raid on Iheyajima island. The official surrender ceremony was held on 7 September near the Kadena airfield.

Okinawa was the bloodiest battle of the Pacific War. The most complete tally of deaths during the battle is at the Cornerstone of Peace monument at the Okinawa Prefectural Peace Memorial Museum, which identifies the names of each individual who died at Okinawa in World War II. As of 2010, the monument listed 240,931 names, including 149,611 Okinawans, 77,485 Imperial Japanese soldiers, 14,010 US soldiers, and smaller numbers of people from North Korea, South Korea, Taiwan and the UK. The numbers correspond to recorded deaths during the 'Battle of Okinawa' from the time of the US landings in the Kerama islands group on 26 March to the signing of the Japanese surrender on 2 September 1945, in addition to all Okinawan casualties in the Pacific War in the 15 years from the Manchurian Incident, along with those who died in Okinawa from war-related events in the year before the battle and the year after the surrender. Some 234,183 names had been inscribed by the time of unveiling and new names are added each year. 40,000 of the Okinawan civilians killed had been drafted or impressed by the Japanese army and are often counted as combat deaths.

The Americans suffered something in the order of 75,000 to 82,000 casualties, including non-battle casualties, of whom more than 20,195 were dead (12,500 killed in action, and 7,700 died of wounds or non-combat deaths). Killed in action were 4,907 US Navy, 4,675 US Army, and 2,938 US Marine Corps personnel. The several thousand personnel who died indirectly (from wounds and other causes) at a later date are not included in the total.

Aircraft losses over the three-month period were 768 US machines, including those bombing the Kyushu airfields from which kamikaze sorties were launched. Combat losses were 458, and the other 310 were operational accidents. At sea, 368 Allied ships, including 120 amphibious craft, were damaged while another 36 (including 15 amphibious ships and 12 destroyers) were sunk during the Okinawa campaign. The US Navy’s dead exceeded its wounded, with 4,907 killed and 4,874 wounded, primarily from kamikaze attacks.

The US military has estimated that 110,071 Japanese soldiers were killed during the battle, a total including conscripted Okinawan civilians.

A total of 7,401 Japanese regulars and 3,400 Okinawan conscripts surrendered or were captured during the battle. Additional Japanese and renegade Okinawans were captured or surrendered over the next few months, bringing the total to 16,346. The 'Battle of Okinawa' was the first battle in the Pacific War in which thousands of Japanese soldiers surrendered or were taken prisoner. Many of the prisoners were native Okinawans who had been pressed into service shortly before the battle and were less imbued with the Imperial Japanese army’s no-surrender doctrine. When the US forces occupied the island, many Japanese soldiers put on Okinawan clothing to avoid capture, and some Okinawans came to the Americans' aid by offering to identify these mainland Japanese.

The Japanese lost 16 combat vessels, including the super-battleship Yamato. Early claims of Japanese aircraft losses put the total at 7,800, but later examination of Japanese records revealed that the actual Japanese aircraft losses at Okinawa were far below often-repeated US estimates for the campaign. The number of conventional and kamikaze aircraft actually lost or expended by the 3rd Air Fleet, 5th Air Fleet and 10th Air Fleet, combined with about 500 lost or expended by the Imperial Japanese army at Okinawa, was approximately 1,430. The Allies destroyed 27 Japanese tanks and 743 pieces of artillery (including mortars, anti-tank and anti-aircraft guns), some of them eliminated by the naval and air bombardments but most destroyed by US counter-battery fire.

Some of the other islands that saw major battles in World War II, such as Iwo Jima, were uninhabited or had been evacuated. Okinawa, by contrast, had a large indigenous civilian population. US Army records from the planning phase of the operation made the assumption that Okinawa was home to about 300,000 civilians. According to various estimates, between one-tenth and one-third of these died during the battle, or between 30,000 and 100,000 people. The official US 10th Army count for the whole campaign is a total of 142,058 recovered Japanese bodies including those civilians pressed into service by the Imperial Japanese army, with the deduction made that about 42,000 were non-uniformed civilians who had been killed in the crossfire. During the battle, the US forces found it difficult to distinguish between civilians and soldiers, and thus it became common for them to shoot at Okinawan houses.

In its history of the war, the Okinawa Prefectural Peace Memorial Museum presents Okinawa as being caught between Japan and the USA. During the 1945 battle, the Imperial Japanese army showed indifference to the safety of Okinawans, and its soldiers used civilians as human shields or killed them. The Japanese military also confiscated food from the Okinawans and executed those who hid it, leading to mass starvation, and also forced civilians out of their shelters. Japanese soldiers also killed about 1,000 people who spoke in the Okinawan language in order to suppress spying. The museum writes that 'some were blown apart by [artillery] shells, some finding themselves in a hopeless situation were driven to suicide, some died of starvation, some succumbed to malaria, while others fell victim to the retreating Japanese troops.'

With the impending Japanese defeat, civilians often committed mass suicide, urged on by the Japanese soldiers who told locals that victorious US soldiers always went on a rampage of killing and raping. Persuaded by Japanese propaganda to believe that US soldiers were barbarians who committed ghastly atrocities, mant thousands of civilians killed their families and themselves to avoid capture by the US forces. Some threw themselves and their family members from the southern cliffs where the Peace Museum now resides. Okinawans 'were often surprised at the comparatively humane treatment they received from the American enemy'. The US forces did not pursue a policy of torture, rape, and murder of civilians as Japanese military officials had warned.' The US Military Intelligence Corps' combat translators managed to convince many civilians not to kill themselves. Survivors of the mass suicides also blamed the indoctrination of their education system of the time, in which the Okinawans were taught to become 'more Japanese than the Japanese', and were expected to prove it.

Witnesses and historians claim that soldiers, mainly Japanese troops, raped Okinawan women during the battle. Rape by Japanese troops reportedly 'became common' in June, after it became clear that the Imperial Japanese army had been defeated. US Marine Corps officials in Okinawa and Washington have said that they knew of no rapes by US personnel in Okinawa at the end of the war, but there are many credible testimony accounts which note that a large number of rapes were committed by US forces during the battle. This includes stories of rape after trading sexual favours or even marrying Americans, such as the alleged incident in the village of Katsuyama, in which civilians said they had formed a vigilante group to ambush and kill three black US soldiers who, they claimed, would frequently rape local girls.

Nine out of every 10 of the island’s buildings on the island were destroyed, along with countless historical documents, artifacts and cultural treasures, and the tropical landscape was turned into 'a vast field of mud, lead, decay and maggots'. The military value of Okinawa 'exceeded all hope'. Okinawa provided a fleet anchorage, troop staging areas and airfields in proximity to Japan. The USA cleared the surrounding waters of mines in 'Zebra', occupied Okinawa and established the US Civil Administration of the Ryukyu Islands, a form of military government.

Because the next major event following the 'Campaign for Okinawa' was 'the total surrender of Japan', the effect of this battle is more difficult to consider. As a result of the Japanese surrender, the next anticipated series of battles, namely the invasion of the Japanese home islands, was not needed and all military strategies on both sides which presupposed this apparently-inevitable next development were immediately rendered moot.