The islands of Palau and the Marianas formed the principal strong points in a chain of islands that Tojo regarded as “the last defense line” to the east. For the Americans, they represented important targets for several reasons: Palau was a barrier to the Philippines, the Marianas afforded the Japanese land-based air cover, and conversely, the Marianas would offer the Americans a base from which to deploy heavy bombers against Japan. In the summer and fall of 1944, the Americans assaulted these targets sequentially, securing first the Marianas and then Palau on their way to the Philippines.
Both targets were hit by carrier raids early in 1944. These attacks were not specifically a part of the campaigns to capture these islands, for in fact the strategy had not yet been determined, but they were a part of a broader naval strategy that battered the weakening Imperial Japanese Navy (IJN) and culminated in the Battle of the Philippine Sea. Accordingly, the raid on the Marianas that began on Feb. 21, and the March 30 attack on Palau, can be considered a part of the campaigns to capture these islands.
The carrier raids began not long after the creation of a Fast Carrier group, dubbed Task Force 58, under Admiral Marc Mitscher. Task Force 58 left Hawaii at the end of January, and awareness of its approach prompted the Japanese to redeploy more valuable naval assets from Truk to Palau, even though Mitscher’s immediate mission was to provide naval support in the Marshalls campaign. Raiding began at Truk on Feb. 17, with a raid on the Marianas following several days later.
At the Marianas, the fighting began a day early, with the Japanese detecting the approach of the task force and launching an air attack late on Feb. 21. This attack had no appreciable effect, and so the carrier raid proceeded on the 22nd, striking airfields on Saipan, Tinian, Guam and Rota as well as any available sea assets. More than 200 Japanese planes were lost in the attack. The attack on Palau on March 30 followed much the same pattern: Japanese reconnaissance detected the approach of the American task force, a night attack by Japanese aircraft resulted in no effective losses, and the next day the American attack devastated Japanese air, naval and merchant marine assets. Here the Japanese lost 17 vessels and 150 airplanes. In another respect, however, the raid on Palau resembled Truk: the major assets of the IJN had departed only days before the attack.
The significance of this fact was felt in June, when the invasion of the southern Marianas commenced. Although all invasion assets, including almost 130,000 soldiers, were transported together, the islands were to be attacked sequentially, with Saipan being captured first, followed by Guam and Tinian, in that order. Among other things, the location of Saipan recommended it as a crucial first target; with Saipan in American hands, Guam and Tinian would be cut off from support from the more northerly Marianas Islands. Thus, the invasion of Saipan was designated the first stage of the operation, dubbed Forager; when it was executed, however, it activated Japanese contingency plans, resulting in a second battle, the Battle of the Philippine Sea.
American naval assets were divided between a ground support force and a defensive reserve. The ground support force included seven battleships, eight escort carriers, eleven cruisers and 38 destroyers. A faster force, mustering fifteen carriers escorted by seven fast battleships, 20 cruisers and 67 destroyers, positioned itself to the west, ready to intercept a Japanese counterattack. The ground support force opened the battle with naval bombardment and air attacks on June 11. Taken as a whole, this introductory bombardment met with mixed results. As many as 150 Japanese planes were destroyed, and some coastal strongpoints were flattened, but the defending ground forces were largely unharmed, ensuring that the American invasion would be contested vigorously.
That invasion began on June 15. Although more than 67,000 American ground troops were bound for Saipan alone, they had to fight their way ashore at first, and as many as 32,000 Japanese soldiers were waiting for them. The first day of fighting brought few gains beyond the creation of two beachheads on the southwest coast, but those beachheads were manned by at least 20,000 Marines. The Japanese attempted to smash the beachheads that night, but American destroyers fired on them, disrupting their formations. They took almost 75% casualties before withdrawing.
Even as the invasion of Saipan finished its first day, a naval battle approached. The Japanese considered the Marianas an essential part of their defenses, and the attack on Saipan prompted them to activate Plan A Go, which mustered the last offensive strength of the IJN, the Mobile Fleet, in an effort to cripple the American fleet off Saipan. The Japanese understood that their carriers, and the planes that they carried, were already outnumbered by the Americans, but A Go was built on the expectation that the airfields of the Marianas and the planes that they supported could supplement the Japanese carriers. Essentially, the islands themselves were to be treated as fixed, and unsinkable, carriers. The preliminary bombardment of Saipan had done much to blunt this strategy; with intelligence reports alerting the US Navy to the approach of the Mobile Fleet, American carriers proceeded to attack the airfields of Guam, Rota, Bonin and Volcano Island on June 16, thoroughly spoiling the Japanese plan. When the Mobile Fleet arrived, it would face Task Force 58 alone.
June 16 brought further amendments to the American invasion plans. The attack on Guam had been slated for June 18, but Admiral Spruance put it on hold, trying to escalate instead the deployment of troops on Saipan. Progress on land was slow, and the 27th Infantry Division was placed ashore to bolster the Marines.
The Mobile Fleet had reached striking distance on June 18, but neither side had a clear notion of the other’s position, and neither wanted to engage prematurely. The Battle of the Philippine Sea therefore opened the following day. Early on the 19th, the Americans detected a Japanese radio broadcast that allowed them to calculate the distance between the two fleets. At 300 miles, this distance was too great for an American air strike, but the Japanese planes were able to make this distance, operating with the expectation that they would be able to land at Guam instead of returning immediately to their carriers.
The Japanese had launched the first of four waves of air attacks, fully expecting to enjoy the support of local air reserves. Indeed, Admiral Ozawa had been assured, falsely, by Admiral Kurita that the land-based reserves were in action and performing admirably. In truth, he had withdrawn the bulk of his aircraft to the Palau Islands and the western Carolines. And so, Ozawa’s pilots went blindly into a firestorm. American aircraft, and the pilots that flew them, outclassed the Japanese planes and pilots, while anti-aircraft fire from the naval vessels also proved deadly. During the first two waves alone, 121 Japanese planes were shot down. The battle is often known as the Great Marianas Turkey Shoot, following a glib comment by an American pilot that soon gained wide currency. For their part, the Japanese managed to inflict light damage to the USS South Dakota, but back at the Japanese battle line, the aircraft carriers Taiho and Shokaku were sunk by American submarines, the USS Albacore and USS Cavalla.
Despite the wide disparity in results, the Japanese did not withdraw that night, nor on the next day, June 20. Admiral Ozawa received reports that greatly overestimated the accomplishments of his pilots, and he thought that he could indeed drive the Americans from the Marianas. Instead, the fast component of Task Force 58 was able to locate the Japanese fleet in the afternoon, and hastened with all speed to press the attack. Admiral Mitscher launched an air attack that night, sinking a third Japanese carrier, the Hiyo, as well as two oil tankers. Two more carriers, the Zuikaku and Chiyoda, the battleship Haruna and the heavy cruiser Maya were also heavily damaged as the Japanese retreated. Most importantly, the Mobile Fleet was left with only 35 operational aircraft.
It was not feasible for Task Force 58 to pursue the Japanese in a timely manner. One consequence of carrier operations by night was the loss of as many as 80 airplanes when the pilots were unable to land safely on their carrier decks. Most of those pilots survived and were rescued, but the time that these rescues took allowed the Mobile Fleet to escape.
Ground combat on Saipan continued for weeks. Most of the island had been captured by the Americans by the 27th of June, but surviving units of the Japanese Army fought hard until July 9. 30,000 Japanese soldiers were killed; many civilians chose suicide over capture. The opening battles of the Marianas Campaign had concluded, and among their consequences was the resignation of Tojo Hideki from his government posts on July 18. The Marianas Campaign continued with the invasion of Guam on July 21 and of Tinian on July 24. Tinian was secured on Aug. 1, but fighting on Guam continued, with major combat ending on Aug. 10.
The Palau Islands were not a part of the Marianas Campaign, per se, but they were secured shortly thereafter, in a preliminary phase of the Philippine Campaign that was executed in September, 1944. After a carrier attack on Sept. 8, the island of Peleliu came under ground attack by the 1st Marine Division on September 15. It was not until Nov. 7 that the island, and with it the Palaus as a whole, were secured. The last of Japan’s defensive line in the Pacific had been swept away, and major assets from the Philippines and Formosa to Okinawa and the Japanese home islands were exposed to attack.
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