These acquisitions dramatically increased Japanese power in the Pacific and created a potential major problem for the United States, as the Carolines straddled the sea-lanes between Hawaii and both the Philippines and China. Indeed, Japanese control of the Carolines caused so much concern that it spurred development of the amphibious warfare doctrine of the U.S. Marine Corps during the interwar period, a process that accelerated after Japan fortified Ponape, Truk, Yap, and Peleliu in the 1930s.
Following the entry of the United States into World War II in 1941, Japanese units in the Solomons and Gilberts were gradually destroyed or isolated by U.S. forces pushing across the Central Pacific. Kwajalein Atoll fell on 7 February 1944, and U.S. Fifth Fleet forces under Admiral Raymond A. Spruance accelerated preparations to capture Eniwetok Atoll as part of an overall plan approved by the Combined Chiefs of Staff in December 1943. The plan called for the seizure of key islands in the Marianas as bases to support a strategic bombing campaign against Japan and for selected attacks to support the South Pacific forces of General Douglas MacArthur.
To cover the Eniwetok landings, however, certain bases in the Carolines first had to be neutralized. Between 15 and 26 February 1944, B-24 Liberator bombers from Major General Willis H. Hale's Seventh Army Air Force struck Ponape. The Eniwetok landings took place on 17 February, and on that day and the next, aircraft carriers from Vice Admiral Marc A. Mitscher's Task Force 58 launched more than 30 raids on Truk, which served as the major forward Japanese fleet anchorage and base in the Central Pacific. Each of the raids included at least 150 planes, and together, they destroyed more than 250 Japanese aircraft and some 200,000 tons of ships, including 2 light cruisers, 1 destroyer, 2 submarine tenders, 1 aircraft ferry, 6 tankers, and 17 merchant ships.
Eniwetok fell on 22 February, and Mitscher's airmen carried out more attacks on Truk on 29 and 30 April. Those attacks, combined with significant shore bombardment by Spruance's battleships, destroyed another 100 Japanese planes. The cumulative effect was so great that the Joint Chiefs of Staff (JCS) chose to bypass Truk and move westward, isolating the substantial Japanese garrison there.
Between June and August, U.S. forces fought the Battle of the Philippine Sea and seized Saipan, Tinian, and Guam in the Marianas, then continued west to attack the Philippines. To cover the initial Philippine landings on Mindanao and Morotai, U.S. planners intended to capture both Peleliu and Yap in the Carolines for use as air bases and forward staging areas. Those plans changed, however, following the September 1944 raids on the Philippines by Mitscher's Task Force 38 of Admiral William F. Halsey's Third Fleet. Halsey found Japanese defenses so weak that he recommended bypassing Morotai, Mindanao, Yap, and Peleliu and moving ahead with the attack on Leyte in October. The JCS agreed but decided to launch the landings on Peleliu and Morotai anyway because the troops for those attacks were already embarked.
Morotai fell on 15 September, the same day that Marines of the 1st Division landed on Peleliu and began one of the most grueling and perhaps unnecessary campaigns of the war. For the first time, the Japanese chose not to defend the beaches of an island under assault. Instead, the 5,300 defenders burrowed into the coral and prepared a main line of defense well inland. They counterattacked frequently; made use of underground tunnels, bunkers, and caves; and fought a battle of attrition in heat that sometimes reached more than 120 degrees. By the time the Peleliu Campaign ended on 25 November, more than 1,950 U.S. troops had been killed, and a regiment of the Army's 81st Division had been brought in as reinforcements. Whether the island needed to be taken and whether it materially aided the capture of the Philippines is extremely doubtful.
And yet, if Peleliu was a mistake, U.S. forces compensated by performing brilliantly throughout the rest of the Carolines. A regimental combat team of the 81st Division took Ulithi Atoll on 23 September, and in less than two weeks, the U.S. Navy was utilizing its splendid large anchorage for attacks against Formosa. The rest of the 81st Division took Angaur (in Palau, near Peleliu) from 1,600 Japanese defenders on 23 October, and with that, the Caroline Campaign came to a close.
Although no decisive battles were fought during the campaign, it was a vital stepping stone toward victory in the Battle of the Philippine Sea and in the conquest of the Marianas and the Philippines. Ulithi became the major U.S. forward fleet anchorage for the duration of the war and played a critical role in the eventual defeat of Japan. Moreover, the strategy of island-hopping reached maturity in the Carolines, as did the evolution of the U.S. Navy's fast-attack carrier groups and the concept of refueling and replenishing at sea. In these and other subtle ways, the campaign played an integral if underappreciated role in the final outcome of the war. One measure of the success of the U.S. strategy may be found in the experience of the British naval squadron that returned to raid Truk in June 1945. By then, that island had been so pummeled by U.S. attacks and its garrison so emaciated by isolation and lack of supplies that the British had no targets worthy of the name. Truk was little more than a prison for its defenders. Lance Janda
Gailey, Harry A. Peleliu, 1944. Annapolis, MD: Nautical and Aviation Publishing, 1983.; Gayle, Gordon D. Bloody Beaches: The Marines at Peleliu. Washington, DC: Marine Corps Historical Center, 1996.; Morison, Samuel E. History of United States Naval Operations in World War II. Vols. 2, 4, 5, 9, 10, and 11. Boston: Little, Brown, 1947–1952.; Morison, Samuel E. History of United States Naval Operations in World War II. Vol. 8, New Guinea and the Marianas, March 1944–August 1944. Boston: Little, Brown, 1953.; Morison, Samuel E. History of United States Naval Operations in World War II. Vol. 12, Leyte, June 1944–January 1945. Boston: Little, Brown, 1958.