Mariana and Palau Islands campaign

• 1. Introduction

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  The Mariana and Palau Islands campaign was one of the most consequential offensives the United States launched in the Pacific during World War II, and its outcome would reach all the way to the Japanese home islands. Between June and November 1944, American forces drove deep into Imperial Japan's defensive perimeter in the central Pacific. The questions worth sitting with are these: why did the United States choose these particular islands, what price did both sides pay to control them, and what did those volcanic specks of land ultimately make possible?

  The campaign had a formal designation inside the American planning system: Campaign Plan Granite II. It rolled together two separate operations. Operation Forager targeted the Mariana Islands. Operation Stalemate targeted Palau. A third operation, called Operation Causeway, was drawn up to invade Japanese-controlled Taiwan but was never executed. Together, Forager and Stalemate would pull over a hundred and twenty-seven thousand troops, fifteen aircraft carriers, seven battleships, and more than nine hundred planes into one of the war's most decisive sequences of fighting.

• 2. Strategic Design

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  Admiral Chester W. Nimitz held overall command of the campaign, and the logic behind it was layered. The immediate predecessor had been the Gilbert and Marshall Islands campaign, and Granite II was the next step in a deliberate march across the central Pacific. Three goals drove the plan. First, American planners wanted to neutralize Japanese bases in the central Pacific so they could no longer threaten Allied movements. Second, capturing these islands would support the drive to retake the Philippines. Third, and perhaps most significantly, possession of the Marianas would put American airfields within striking range of Japan itself.

  Before a single landing craft hit a beach, American planners ran a deception effort called Operation Wedlock. Starting in October 1943, a joint army and navy radio task force set up at Adak, Alaska began broadcasting fabricated radio traffic. The fake signals suggested that a formation called the I Alaskan Corps was preparing to invade the Kurile island group. The traffic was directed at equally fictitious units: the IX Amphibious Force and the 9th US Fleet. The goal was to draw Japanese attention and resources northward, away from the real axis of advance in the central Pacific.

• 3. The Force Assembled

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  Vice Admiral Raymond A. Spruance commanded the Fifth Fleet for the campaign. Within that fleet, Task Force 58 fell under Vice Admiral Marc Mitscher, and its composition was staggering: fifteen carriers, seven battleships, eleven cruisers, eighty-six destroyers, and more than nine hundred planes. Vice Admiral Richmond K. Turner commanded the amphibious invasion force separately, which brought fifty-six attack transports, eighty-four landing craft, and more than a hundred and twenty-seven thousand troops to bear.

  United States Marine Corps and Army forces would carry out the actual landings, backed by Navy support. The scale of the combined arms task force reflected how seriously American commanders understood the challenge ahead. Japanese forces in the central Pacific had defended island positions tenaciously throughout the war, and the Marianas and Palau would be no different.

• 4. The Great Marianas Turkey Shoot

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  American forces landed on Saipan in June 1944. The Japanese response came swiftly at the fleet level: the Imperial Japanese Navy's Combined Fleet sortied to attack the U.S. Navy force supporting the Saipan landings. What followed on the 19th and the 20th of June became known by two names. Formally, it was the Battle of the Philippine Sea. Informally, American aviators called it the Great Marianas Turkey Shoot.

  The result was a decisive Japanese defeat. Japanese naval aviation suffered heavy and irreplaceable losses, both carrier-borne aircraft and land-based planes. The losses were not merely large; they were losses Japan could not recover from. The carriers survived the battle, but without experienced pilots and planes to fill them, they would be of limited offensive value for the rest of the war. The destruction of Japanese air power in this engagement changed the nature of the Pacific War in a fundamental way, leaving American forces with sharply reduced opposition from the air for subsequent operations.

• 5. Island by Island

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  Saipan was secured in July 1944 after heavy fighting. American forces then landed on Guam and Tinian in July as well, with both islands secured by August 1944. The fighting on each island was brutal; Japanese forces did not surrender positions willingly, and the terrain of each island imposed its own costs on the attackers.

  With the Marianas in American hands, construction crews began building airfields on Saipan and Tinian. Those airfields became the launch platforms for B-29 Superfortress strategic bombing missions against the Japanese home islands. The missions continued until the end of World War II. They included the nuclear attacks on Hiroshima and Nagasaki. The runways carved out of Tinian and Saipan were not an afterthought; they were the operational reason the islands had been seized.

• 6. Peleliu and Angaur

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  Operation Stalemate opened in September 1944 when Marine and Army forces landed on Peleliu and Angaur in the Palau island group. The objective was to secure the flank for American forces preparing to attack Japanese positions in the Philippines. Peleliu's battle ran from the 15th of September to the 27th of November 1944. Angaur's fighting concluded on the 22nd of October 1944, having started on the 17th of September.

  Both islands were eventually secured in November 1944, but the campaign came at a steep cost in casualties. The main Japanese garrison in the Palaus sat on Koror, and American commanders chose to bypass it entirely rather than assault it directly. That garrison remained there, isolated and cut off, until Japan's capitulation in August 1945, when it finally surrendered.

• 7. What Came Next

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  Allied forces landed in the Philippines in October 1944, the direct follow-on that the Marianas and Palau campaign had been designed to support. After the Philippines, the campaign against Japan continued with landings in the Volcano and Ryukyu Islands beginning in January 1945. Each step had been threaded through a logical sequence, with the Mariana and Palau islands as the hinge.

  The bypassed garrison at Koror sitting out the war until August 1945 stands as one of the stranger footnotes of the campaign. While B-29s flew missions from Tinian to Hiroshima and Nagasaki, a Japanese force in the same island group simply waited, cut off, until news of surrender reached them.