The 'Battle of Saipan' was fought between US and Japanese forces for the island of Saipan in the Mariana islands group within the context of the US 'Forager' strategic operation (15 June/9 July 1944).

The US assault on the Mariana islands group was of strategic significance, for it was another advance toward the Japanese home islands by the forces of Admiral Chester W. Nimitz’s Pacific Ocean Areas command and also provided the US Army Air Forces with bases from which their new Boeing B-29 Superfortress four-engined heavy bomber forces could destroy Japan’s cities and industries, and also triggered the 'A' operation whose 'Battle of the Philippine Sea' was a Japanese strategic naval defeat.

Additionally, the loss of Saipan with the deaths of at least 29,000 troops and heavy civilian casualties, precipitated the resignation of Japan’s prime minister, General Hideki Tojo.

In the campaigns of 1943 and the first half of 1944, the Allies had taken the Solomon island, the Gilbert island and the Marshall island groups, as well as the Papuan peninsula of New Guinea. This left the Japanese in the Pacific theatre holding the Philippine islands group, Caroline islands group, Palau islands group and Mariana islands group.

The Mariana islands group had not been a key element of the USA’s pre-war planning (War Plans Orange and Rainbow) because the islands lie well to the north of the maritime route between the Hawaiian and Philippine island groups: the USA believed that the latter would hold any Japanese invasion for a time sufficient for US reinforcements to be gathered and transported to these islands for the relief of the forces holding out in that theatre. At the time, the USA’s naval, air and sea logistics capabilities were seen as inadequate for the support of military operations against a place so far from potential land-based support. By a time early in 1943, however, Admiral Ernest J. King, the US chief of naval operations and commander-in-chief of the US Fleet, had become increasingly convinced of the strategic significance of the island group as a base for submarine operations and air facilities for B-29 bombing of the Japanese home islands. From the bases in these islands, the US forces could sever the Japanese communications between the home islands and the Japanese forces to the south and west. From the Mariana islands group, Japan would be well within the range of a strategic air offensive relying on the 3,250-mile (5230-km) operational radius of the B-29 long-range bomber.

The capture of the Mariana islands group was formally endorsed at the 'Sextant' inter-Allied conference in Cairo during November 1943. The plan had the support of US Army Air Forces' planners because airfields on Saipan could be created to support B-29 operations, within range of the Japanese home islands, and unlike a China-based alternative, was not open to Japanese counterattacks once the islands had been secured. However, General Douglas MacArthur, the Supreme Allied Commander of the South-West Pacific Area, objected strongly to any plan which would delay the return of his forces to the Philippine islands group. His objections were routed through formal channels as well as bypassing the Joint Chiefs-of-Staff, appealing directly to Secretary of War Henry Stimson and President Franklin D. Roosevelt.

MacArthur’s objections were not without tactical reasoning based on the experience of the 'Galvanic' seizure of Tarawa atoll, but were voiced before the vastly improved experience of the 'Flintlock' and 'Catchpole' operations to take the Gilbert and Marshall island groups, the rapid and sizeable increase in US naval strength, the successful 'Hailstone' attack on Truk and the Caroline islands group by carrierborne aircraft, and the co-ordinated armed services experience gained in all these operations by Nimitz’s Pacific Ocean Areas.

MacArthur secured authorisation for operations which had not been part of the US original plan. These operations included a westward advance along the northern coast of New Guinea and the seizure of Morotai island as part of an advance toward the Philippine islands group. This allowed MacArthur to keep his personal pledge to liberate the Philippine Republic, made in his celebrated 'I shall return' speech, and also allowed the active use of the large forces built up in the South-West Pacific Area. Expecting an attack somewhere on their perimeter, the Japanese thought that an attack on the Caroline islands group was the USA’s most probably next move. To reinforce and supply their garrisons, they needed naval and air superiority, so 'A' was readied for June 1944 as a major naval attack, centred on carrierborne air power, to fall on the US forces wherever they landed in the Pacific.

Codenamed 'Tattersalls', Saipan is the second largest island of the Marianas group, and lies 100 miles (160 km) to the north-east of Guam, the group’s largest island. The island of Tinian is 3 miles (4.8 km) off the southern tip of Saipan, and Farallon de Medinilla, the southernmost island of the Northern Marianas group, is about 30 miles (48 km) to the north-east.

Saipan is 12.5 miles (20.1 km) long on its north-east/south-west axis and 5.5 miles (8.85 km) wide across its centre, and possesses an area of 45.9 sq miles (119 km²). The island’s coast is 54 miles (86.9 km) long and for the most part is faced with cliffs of varying height leaving only 14 miles (22.5 km) of beach, mostly on the western side. The island’s western side and southern end possess most of the usable beaches, but are also fringed by barrier reefs. On the island’s southern tip, the fringing reef’s edge extends farther offshore as it runs up the eastern coast, up to 1,500 yards (1370 m) off the central portion of the island at Mutcho Point. To the north of this point is Tanapag Harbor, which is formed by a long, submerged coral reef arm curving out from the upper part of the eastern coast, after which the reef runs back close ashore along the upper eastern coast. The southern end of the reef arm is off of Mutcho Point, and a channel had been dredged to provide access to Tanapag Harbor.
This harbour does not indent the coast, but the offshore reef arm provides some protection for what is called the Saipan Lagoon. The harbour is defined by Mutcho Point on its southern side and the town of Garapan, the island’s largest semi-urban area, and Flores Point on the northern side. It is between 20 and 50 ft (6.1 and 15.25 m) deep. The port possessed four large piers, the largest of them some 700 yards (640 m) long with spur piers. About 3,000 yards (2745 m) to the north-west of Tanapag Harbor is Maniagassa island, which is about 300 yards (275 m) in diameter. Projecting from the south-eastern comer of the island is the Nafutan peninsula and 4,000 yards (3660 m) to the north across Magicienne Bay, also known as Lau Lau Bay, is the Kagman peninsula. The bay’s shore is faced by broken and cave-riddled cliffs, and fringed by a narrow beach with coral outcroppings and a coral reef, the only one on the island’s eastern side.

The southern third of the island is a rolling plateau 200 to 300 ft (61 to 91 m) above sea level. The island’s main 4,500-ft (595-m) Aslito airfield was located on the plain at the base of the Nafutan peninsula. On the lower western coast is a plain about 2,000 yards (1830 m) wide, on which is located the marsh-surrounded freshwater Lake Susupe near Afetna Point. To the south of this point is the island’s second largest town, Charan Kanoa, and to its north was an emergency landing strip. Another airfield was located on the island’s northern end at Marpi Point at the base of the 833-ft (254-m) Mt Marpi, but this had not yet been completed. A seaplane base was located at Flores Point on the northern edge of Tanapag Harbor. The island’s centre is dominated by the 1,554-ft (474-m) Mt Tapotchau rising from the northern edge of the southern plateau. A rugged ridge line, between 400 and 934 ft (122 and 285 m) high, extends 7 miles (11.25 km) northward to Mt Marpi. Caves and ravines are common in the hills.

Some 70% of the island was planted with sugar cane, whose presence was a major impediment to ground operations. The rest of the island, the hilly areas, was covered by low scrub trees, brush and grasses of some height and density.

Aslito airfield had been built in 1934 as the first such facility on the Mariana islands group, and the seaplane base in Tanapag Harbor had been constructed in 1935. Work on the emergency airstrip and the incomplete airfield on the northern end had begun in 1944.

An improved road followed the western coast from the southern end’s Cape Obiam to Marpi Point on the northern end. The road looped round the northern end and reconnected with itself on the western coast. Three other roads crossed the northern ridge connecting to a road running down the eastern coast to the Kagman peninsula, along Magicienne Bay to Aslito airfield and around the southern end where it connected with the west-coast road. The island also possessed an extensive narrow-gauge railway system for the movement of cut sugar cane: this railway ran around most of the coast.

The island’s population was more than 20,000 Japanese, about 4,000 indigenous Chamorros and 1,000 Kanakas. Some Japanese civilians, mainly women and children, had been evacuated before the launch of 'Forager', but many women and children remained to suffer in the coming battle.

Even minimal defensive installations had not been built on Saipan until 1940/41, though the US forces feared that the islands were being fortified. Lieutenant General Yoshitsugu Saito’s 43^rd Division (118^th, 135^th and 136^th Regiments) had been despatched from the Japanese home islands to Saipan late in May 1944. The 1^st Expeditionary Unit also arrived from Japan in May and was reorganised as Colonel Yoshiro Oka’s 47^th Independent Mixed Brigade. Two more infantry battalions, detached from other islands, as well as artillery, anti-aircraft, tank, engineer and service units were additionally present. Imperial Japanese navy units included the regimental-size 41^st Base Force and 55^th Base Force, the parachute-trained battalion-size 1^st Yokosuka Special Naval Landing Force and service units under the command of the 5^th Special Base Force. The island thus contained 25,500 army troops and 6,200 naval personnel. The 43^rd Division doubled as the Northern Marianas Army Group that was responsible for the defence of Saipan and Tinian.

Under the control of Admiral Raymond A. Spruance’s 5^th Fleet, the two main elements of the US forces to fall on the Mariana islands group were Vice Admiral Richmond K. Turner’s Northern Attack Force (Task Force 2) and Lieutenant General Holland M. Smith’s Expeditionary Troops. Saipan was the objective of the 59,800 men of the Northern Troops and Landing Force (TF56.1) based on the V Amphibious Corps, which was the joint marine and army force under Smith’s command. After final preparations and rehearsals in May for 'Forager', TF56.1 departed the Hawaiian islands group between 25 and 30 May. Under the V Amphibious Corps were Major General Thomas E. Watson’s 2^nd Marine Division (2^nd, 6^th, 8^th, 10^th [artillery] and 18^th [engineer] Marines), Major General Harry Schmidt’s 4^th Marine Division (14^th [artillery], 20^th [engineer], 23^rd, 24^th and 25^th Marines), Major General Ralph C. Smith’s 27^th Division (105^th, 106^th and 165^th Infantry), and the XXIV Corps Artillery. While the V Amphibious Corps was a marine command controlling the landing force for Saipan and later Tinian, its combined artillery assets were controlled by the army’s XXIV Corps Artillery under the command of Brigadier General Arthur M. Harper.

The preliminary bombardment of Saipan began on 13 June by a naval force comprising seven modern fast battleships, 11 destroyers and 10 fast minesweepers under the command of Vice Admiral Willis A. Lee. The battleships delivered 2,400 16-in (410-mm) shells, but to avoid potential minefields, the fire was from a range of 10,000 yards (9145 m) or more, and crews were inexperienced in shore bombardment. On the following day, two naval bombardment groups led by Rear Admiral Jesse B. Oldendorf arrived off Saipan. This force was the main naval fire support for the seizure of the island and comprised seven older battleships, 11 cruisers and 26 destroyers, along with destroyer transports and fast minesweepers. The crews of these older battleships, commissioned between 1915 and 1921, were trained in shore bombardment and the battleships were able to move into closer range.

The US landings began at 07:00 on 15 June as more than 300 LVT tracked amphibious vehicles delivered 8,000 marines onto the western coast of Saipan by about 09.00 under the covering fire of 11 fire-support ships. The 2^nd Marine Division and 4^th Marine Division were the the left- and right-hand formations of the assault force, with Afetna Point the divider between the two division’s assault beaches The naval force comprised the battleships Tennessee and California, the heavy cruiser Indianapolis, the light cruiser Birmingham, and the destroyers Norman Scott, Monssen, Coghlan, Halsey Powell, Bailey, Robinson and Albert W. Grant.
Careful artillery preparation, including the placement of flags in the lagoon to indicate the range, allowed the Japanese to destroy about 20 LVTs, and the Japanese had also placed barbed wire entanglements, artillery, machine gun emplacements and trenches to maximise their ability to inflict loss on the US forces. By the fall of night, however, the 2^nd and 4^th Marine Divisions had established a beach-head about 6 miles (9.7 km) wide and 880 yards (805 m) deep. The Japanese counterattacked during the night but were repelled with heavy losses. On 16 June, units of the US Army’s 27^th Division landed to the right of the 4^th Marine Division and advanced on the airfield at Aslito. Again the Japanese launched a nocturnal counterattack, and again this failed. On 18 June, Saito abandoned the airfield.

The invasion surprised the Japanese high command, which had been expecting an attack farther to the south. Admiral Shigetaro Shimada, commander-in-chief of the Imperial Japanese navy, nonetheless saw an opportunity to use the 'A' naval forces to attack the US Navy elements around Saipan, and on 15 June gave the order to attack. The resulting 'Battle of the Philippine Sea' was a disaster for the Japanese, who lost three aircraft carriers and hundreds of warplanes.

The fighting on Saipan was a hopeless effort for the Japanese, who lacked all possibility of reinforcement and resupply, but were nonetheless determined to fight to the last man. Saito organised his troops into a line anchored on Mt Tapochau in the defensible mountainous terrain of central Saipan. The nicknames given by the US forces to the geographical features of the battle, such as 'Hell’s Pocket', 'Purple Heart Ridge' and 'Death Valley', indicate the severity of the fighting. The Japanese used the many cave complexes in the volcanic landscape to delay the attackers: they hid during the day and sortied by night. But the Americans gradually developed tactics for clearing the caves by using teams equipped with flamethrowers and/or satchel charges, supported by artillery and machine guns, to seal off the mouths of any cave suspected of harbouring Japanese troops.

The operation was marred by inter-service controversy when Lieutenant General Holland Smith, a marine officer, became dissatisfied with the performance of the 27^th Division and relieved its commander, Major General Smith, an army officer, and replaced him with another army officer, Major General George W. Griner. However, Holland Smith had not inspected the terrain over which the 27^th Division was tasked to advance. Essentially, it was a valley surrounded by hills and cliffs under Japanese control. The 27^th Division sustained heavy casualties and eventually, under a plan developed by Ralph Smith and implemented after his relief, had one battalion hold the area while two other battalions successfully flanked the Japanese.

The 27^th Division advanced to the east and reached Nafutan Point, on the south-eastern tip of Saipan, on 28 June while it main strength had already wheeled to the north to advance with the marine divisions on its flanks. The 4^th Marine Division, on the army formation’s left, had also driven to the east across the island to reach Magicienne Bay and then also turned to the north to drive forward up Saipan’s eastern coast. The 2^nd Marine Division had emerged from its sector of the initial beach-head to wheel left and advance to the north along Saipan;s western coast. By 30 June the forces of the V Amphibious Corps had reached a line extending eastward right across the island from Garapan on the western coast, and continued their drive to the north.

By 6 July, the Japanese were left with nowhere to retreat, and Saito made plans for a final banzai suicidal charge. On the fate of the remaining civilians on the island, Saito said that 'There no longer remains any distinction between civilians and troops. It would be better for them to join in the attack with bamboo spears than to be captured.' At dawn on 7 July, with a group of 12 men carrying a red flag in the lead, the remaining able-bodied troops, totalling about 4,000 men, charged forward in the final attack to the south from the area of Makunsha on the north-western coast. Behind the uninjured came the wounded, with bandaged bodies, on crutches and barely armed. The Japanese surged over the US front line, engaging both army and marine units. The 1 and 2/105^th Infantry were almost destroyed, losing considerably more than 650 men killed and wounded. The two battalions fought back, as did the regimental headquarters and supply elements of 3/10^th Marine Artillery. The result was the death of more than 4,300 Japanese and US losses of more than 400 dead and 500 wounded. The attack of 7 July was the largest Japanese banzai charge of the Pacific War.

By 16.15 on 9 July, Turner could announce that Saipan was officially secured. Saito, along with two subordinate commanders, committed ritual suicide in a cave. Nagumo, the naval commander who had led the Japanese carriers in the 'Ai' attack on Pearl Harbor, also committed suicide in the closing stages of the battle: he had been the commander of the Japanese naval air forces stationed on the island.

In the end, almost the island’s entire garrison of at least 29,000 men, died. For the Americans, the victory was the most costly to date in the Pacific War: of the 71,000 men who landed, 2,949 had been killed and 10,464 wounded.

Holland Smith and the V Amphibious Corps had anticipated that the taking of Saipan would be very difficult and wanted the support of a mechanised flamethrowing capability. The necessary research, development and procurement made that a long-term prospect,so the V Amphibious Corps had bought from Canada 30 Ronson flamethrowers and requested that the US Army’s Chemical Warfare Service in the Hawaiian islands group install them in M3 Stuart light tanks to create the M3 Satan. 'Seabee' personnel of the Chemical Warfare Service had 24 ready for the battle, in which they played a significant role.

While the battle came to what the US forces deemed an official end on 9 July, Japanese resistance still persisted in the form of Captain Sakae Oba and 46 other soldiers who survived with him during the last banzai charge. After the battle, Oba and his men led many civilians throughout the jungle of the island to escape capture by the Americans, while also conducting guerrilla attacks on the US forces pursuing them. The Americans tried numerous times to hunt them down, but failed as a result of the Japanese group’s speed and stealth. In September 1944, the marines began to undertake patrols in the island’s interior, searching for survivors who were raiding their camp for supplies. Although some of his men wished to fight, Oba asserted that their primary concerns were to protect the civilians and to stay alive to continue the war. At one point, the Japanese soldiers and civilians were almost captured by the Americans as they hid in a clearing and ledges of a mountain, some were less than 20 ft (6.1 m) above the heads of the marines, but the Americans failed to see them. Oba’s resistance lasted for more than one year before Oba finally surrendered on 1 December 1945, three months after the official surrender of Japan.

At least 25,000 Japanese civilians lived on Saipan at the time of the battle. Civilian shelters were located in almost every area of the island, with very little difference from military bunkers noticeable to US attackers. The standard method of clearing suspected bunkers was the use of high explosive charges and/or high explosives charges augmented with gelignite, napalm or Diesel fuel. The combination of such weapons and the tactics of close-quarter fighting inevitably caused high civilian casualties.

The US forces erected a civilian prisoner camp on 23 June 1944, and this soon accommodated more than 1,000 persons. The camp’s electric lighting was left on at night in the hope of attracting other civilians with the promise of hot food and no risk of being shot accidentally.

More than 1,000 Japanese civilians committed suicide in the last days of the battle to take the offered privileged place in the afterlife, some jumping from places later named 'Suicide Cliff' and 'Banzai Cliff'.

With the capture of Saipan, the US forces were now 1,300 miles (2095 km) closer to the Japanese home islands, and Holland Smith said that 'It was the decisive battle of the Pacific offensive…it opened the way to the Japanese home islands.' The victory proved to be one of the most important strategic events of the war in the Pacific theatre as the Japanese archipelago now lay within striking distance of the US Army Air Forces' fleet of B-29 heavy bombers. From this point on, moreover, Saipan would become the launch point for the recapture of other elements of the Mariana island group and the 'King II' and other operations to retake the Philippine islands group from October 1944. Four months after the island’s capture, more than 100 B-29 bombers from Saipan’s Isely Field were regularly attacking the Philippine islands group, the Ryukyu islands group and the Japanese mainland. In response, Japanese aircraft attacked Saipan and Tinian on several occasions between November 1944 and January 1945, but the US forces' 'Detachment' capture of Iwo Jima island between 19 February and 26 March 1945 ended further Japanese air attacks.

The loss of Saipan was a severe blow to both the military and civilian administration of Tojo, Japan’s prime minister. Soon after the loss of Saipan, a meeting at the Imperial General Headquarters decided that a symbolic change of leadership should be made: Tojo would be replaced and the Emperor Hirohito would have less involvement in day-to-day military affairs, even though he was defined as both head of state and the supreme commander of the Imperial Japanese armed forces according to the Meiji Constitution of 1889. The general staff believed it was now time to distance the imperial house from the apportionment of blame as the tide of war turned against the Japanese. Although Tojo agreed to resign, Hirohito blocked his resignation as he believed Tojo to be Japan’s strongest war leader. After he had failed to shuffle his cabinet, as a consequence of excessive internal hostilities, Tojo conceded political defeat and on 18 July again submitted his resignation, this time unequivocally. His entire cabinet resigned with him. A retired army officer, General Kuniaki Koiso, was appointed prime minister on 22 July but, as a result of the defeat on Saipan, he was prime minister in nothing but name, and was denied by the Imperial General Headquarters from any involvement in military decision-making.

The loss of Saipan also saw a change in the way reporting on the war was presented to the Japanese population. Initially, as the battle started, Japanese accounts concentrated on the fighting spirit of the Imperial Japanese army and the heavy casualties it was inflicting on the US forces. However, anyone with knowledge of Saipan’s geography would have known from the chronology of engagements that the US forces were advancing relentlessly to the north. No more mention of Saipan was made following the final battle on 7 July, which was not itself initially reported to the public. After Tojo’s resignation on 18 July, however, an almost day-to-day and accurate account of the defeat on Saipan was published jointly by the Imperial Japanese army and navy. The reports mentioned the near total loss of all Japanese soldiers and civilians on the island and the use of 'human bullets' (explosive-laden men committed to the attack). The reports had a devastating effect on Japanese opinion: mass suicides were now seen as defeat rather than evidence of the 'Imperial Way'. This was the first time Japanese forces had been depicted accurately in a battle since the 'Battle of Midway', which had been proclaimed a victory.