The Mariana Islands run in a gentle arc about 1,500 miles south of Tokyo: Guam at the southern end, then Rota, Tinian and Saipan, then a string of small volcanic islands toward Japan. In June 1944 the United States sent 535 ships and 127,000 soldiers and Marines to take the southern Marianas. The campaign, code-named Operation Forager, produced the largest carrier battle of the war, the bloodiest American campaign in the Pacific up to that time, and the airfields from which B-29 bombers would burn Japan’s cities and carry the atomic bombs.

The islands

Spain claimed the Marianas in the seventeenth century, and the Chamorro people of the islands lived under Spanish rule for more than two hundred years. After the Spanish-American War of 1898 the United States took Guam; Spain sold the northern Marianas to Germany the following year. Japan seized the German islands in 1914, at the start of the First World War, and governed them after 1920 under a League of Nations mandate as part of its South Seas territories.

Under Japanese rule Saipan and Tinian were turned into sugar islands. Tens of thousands of Japanese, Okinawan and Korean settlers came to work the cane fields and the mills, and by 1944 they far outnumbered the Chamorro and Carolinian islanders. Garapan, Saipan’s main town, had shops, schools, a hospital and a Shinto shrine. Guam, meanwhile, remained an American naval station with a small garrison until Japanese forces landed on 10 December 1941 and its governor surrendered. For the next two and a half years the Chamorro people of Guam lived under a harsh military occupation, described in Chapter 7.

Why the Marianas

Two arguments brought the Americans to the Marianas. The first was naval. Admiral Ernest King, the Chief of Naval Operations, had long argued that the way to defeat Japan was to drive straight across the Central Pacific, through the Gilberts, the Marshalls and the Marianas, cutting Japan’s links to its southern empire and forcing the Japanese fleet to fight. The capture of Tarawa and Kwajalein in November 1943 and February 1944 had opened that road faster than expected.

The second argument was about the B-29 Superfortress. The new long-range bomber could carry several tons of bombs about 1,500 miles and back. From bases in China it could barely reach Japan’s southern islands, and those bases had to be supplied over the Himalayas. From the Marianas it could reach Tokyo and most of Japan’s industrial cities. General Henry Arnold, commander of the Army Air Forces, wanted the islands for his bombers. In March 1944 the Joint Chiefs of Staff directed Admiral Chester Nimitz to seize the southern Marianas, with the landing on Saipan set for 15 June. The bombing campaign that followed is told in Chapter 8 and in this site’s Army Air Forces collection.

Japan's defense line

The Japanese understood the danger. In September 1943 Imperial General Headquarters drew an “absolute national defense sphere” that ran from the Kuril Islands through the Bonins and the Marianas to western New Guinea and Burma. Inside it, positions were to be held at any cost. The Marianas were the keystone. Their loss would put Japan within bomber range and break the line between the home islands and the empire to the south.

Reinforcing the islands was slow and costly. American submarines sank many of the transports sent to the Marianas in the spring of 1944, drowning thousands of soldiers and sending others ashore without their weapons and equipment. The 31st Army under Lieutenant General Hideyoshi Obata was responsible for the Marianas and the Carolines. On Saipan, Lieutenant General Yoshitsugu Saito commanded the 43rd Division and the army troops; Vice Admiral Chuichi Nagumo, who had led the carriers at Pearl Harbor and Midway, headed the Central Pacific Area Fleet from a headquarters on the island. The Saipan garrison numbered about 30,000 men. Many defensive positions were unfinished when the Americans arrived.

The Japanese navy prepared its own plan, A-Go. The Mobile Fleet under Vice Admiral Jisaburo Ozawa, with nine carriers, would wait in the southern Philippines for the Americans to commit themselves. Land-based aircraft in the Marianas and the Carolines would wear down the American carriers first. Then Ozawa would strike from beyond the range of American aircraft, using the islands’ airfields to refuel and rearm his planes. How that plan fared is the subject of Chapter 3.

Gallery · 4 photographs · select to enlarge

The Japanese Marianas before the invasion

The approach

The Central Pacific drive moved quickly in early 1944. Kwajalein fell in the first week of February, and Eniwetok later that month. On 17–18 February the fast carriers of Task Force 58 struck the Japanese fleet base at Truk in the Carolines, sinking or wrecking dozens of ships and hundreds of aircraft; Truk was then left to wither. On 22–23 February the carriers raided the Marianas for the first time, and in late March they struck the Palaus.

By June the American fleet in the Central Pacific was overwhelming. Admiral Raymond Spruance’s Fifth Fleet included Task Force 58 under Vice Admiral Marc Mitscher, with 15 fleet and light carriers, seven fast battleships and about 900 aircraft, and the amphibious forces of Vice Admiral Richmond Kelly Turner. Lieutenant General Holland M. Smith of the Marine Corps commanded the expeditionary troops.

Operation Forager

The plan called for two landing forces. The Northern Troops and Landing Force, under Holland Smith himself, would take Saipan and then Tinian with the 2nd and 4th Marine Divisions, with the Army’s 27th Infantry Division in reserve. The Southern Troops and Landing Force under Major General Roy Geiger, the III Amphibious Corps, would take Guam with the 3rd Marine Division and the 1st Provisional Marine Brigade, with the Army’s 77th Infantry Division in reserve in Hawaii. Guam was to be invaded three days after Saipan; the battle at sea would delay it by more than a month.

The forces sailed from Hawaii, Guadalcanal, Kwajalein and Eniwetok in late May and early June, gathering at Eniwetok and Kwajalein before the final approach. Many of the Marines were veterans of Guadalcanal, Tarawa and Roi-Namur. Navajo Marines of the 2nd, 3rd and 4th Marine Divisions went with them, carrying the code described in this site’s Navajo Code Talkers section.

Softening up

On 11 June Mitscher’s carriers struck the airfields of Saipan, Tinian and Guam with a fighter sweep that destroyed much of the Japanese land-based air strength in the islands before the A-Go plan could use it. Strikes and naval bombardment continued for the next four days. On 13 June the new fast battleships shelled Saipan from long range, with limited effect; on 14 June the older battleships of the bombardment groups, several of them survivors of Pearl Harbor, took over at closer range. Navy underwater demolition teams swam in to survey the reef and the beaches.

The bombardment destroyed many visible targets but left the Japanese artillery in the hills behind the beaches largely intact. Its gunners had registered on the beaches and the reef with marker flags. When the landing craft went in on the morning of 15 June, those guns were waiting. Chapter 2 tells the story of the landing.

Gallery · 5 photographs · select to enlarge

The fleet assembles, June 1944

Sources and further reading

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