On 3 October 1944 American forces in the Pacific Ocean Areas received a directive to seize positions in the Ryukyu Islands (Nansei Shoto). Okinawa is the most important island of the Ryukyu Group, the threshold of the four main islands of Japan. The decision to invade the Ryukyus signalized the readiness of the United States to penetrate the inner ring of Japanese defenses. For the enemy, failure on Okinawa meant that he must prepare to resist an early invasion of the homeland or surrender.
Operation ICEBERG, as the plan for the Okinawa campaign was officially called, marked the entrance of the United States upon an advanced stage in the long execution of its strategy in the Pacific. Some 4,000 miles of ocean, and more than three years of war, separated Okinawa from Pearl Harbor. In 1942 and 1943 the Americans had contained the enemy and thrown him back; in 1944 their attack gathered momentum, and a series of fierce island campaigns carried them toward the Japanese inner stronghold in great strides.
The Allied advance followed two main axes, one through the islands of the Central Pacific, the other through the South and Southwest Pacific. Navy task forces and some other elements operated on both fronts as needed. The result was "unremitting pressure" against Japanese military and naval might, a major objective of American strategy.
Near the close of 1943, a thrust at the Gilbert Islands from the Central Pacific, in which Tarawa, Makin, and Apamama were seized, paved the way for the assault on the Marshalls on 31 January 1944. American forces captured Kwajalein, Majuro, and Eniwetok, and their fleet and air arms moved forward. At the same time, American carriers heavily attacked Truk, and that formidable enemy naval base in the Carolines was thenceforth immobilized. Saipan, Tinian, and Guam in the Marianas fell to American arms in the summer of 1944, and, in the First Battle of the Philippine Sea, the U.S. Navy administered a crushing defeat to the Japanese fleet that tried to interfere with the American push westward. In September and October the Americans occupied Ulithi in the western Carolines for use as an anchorage and advanced fleet base, and took Angaur and Peleliu in the Palau Islands, situated close to the Philippines.
Meanwhile, American forces in the South and Southwest Pacific were approaching Mindanao, southernmost of the Philippine Islands, by advances through the Solomons and New Guinea in which Japanese armies were neutralized and isolated on Bougainville, New Ireland, and New Britain. The capture of Wakde on the northeastern coast of New Guinea in May 1944 was followed by the seizure of Biak and Noemfoor. During the summer a Japanese army attempting to break out from Wewak in Australian New Guinea was subdued. The invasion of Morotai in September placed American forces within 300 miles of Mindanao.{2} (See Map No. 1.)
The ultimate goal of American operations in the Pacific was the industrial heart of Japan, along the southern shores of Honshu between the Tokyo plain and Shimonoseki. American strategy aimed to reach this objective by successive steps and to take advantage, on the way, of Japan's extreme vulnerability to submarine blockade and air bombardment. Throughout most of 1944 Army and Navy staffs in the Pacific Ocean Areas had been planning for the invasion of Formosa (Operation CAUSEWAY) in the spring of 1945. On the basis of the Joint Chiefs of Staff directive of March 1944, the general concept of this operation had been outlined, the availability of troops considered and reviewed many times, and the assignment of task force commanders announced. On 23 August, a joint staff study for CAUSEWAY had been published. It was clear that Admiral Chester W. Nimitz, Commander in Chief, U.S. Pacific Fleet and Pacific Ocean Areas, intended to invade Formosa after Southwest Pacific forces had established positions in the Central and Southern Philippines; CAUSEWAY, in turn, was to be followed by operations against the Ryukyus and Bonins, or against the China coast. Either course would lead eventually to assault on the Japanese home islands.{3}
On 15 September the Joint Chiefs directed Gen. Douglas MacArthur to seize Leyte on 20 October, instead of 20 December as planned, and to bypass Mindanao. At the same time, Admiral Nimitz was instructed to bypass Yap.{4} On the next day Admiral Nimitz reconsidered the Formosa operation. He believed that the early advance into the Central Philippines, with the opportunity of acquiring the desired fleet anchorages there, opened up the possibility of a direct advance northward through the Ryukyus and Bonins rather than through Formosa and the China coast. He reviewed the objectives of CAUSEWAY the establishment of air bases from which to bomb Japan, support China, and cut off the home islands from resources to the south—with reference to the new possibility and in a letter to his Army commanders requested their opinions on the subject.{5}
Map No. 1 — Strategic Situation in the Pacific
Lt. Gen. Robert C. Richardson, Jr., Commanding General, U.S. Army Forces, Pacific Ocean Areas, replied that only those steps should be taken which would lead to the early accomplishment of the ultimate objective—the invasion of Japan proper. From this point of view the occupation of Formosa as a stepping stone to an advance on Japan via the China coast did not, in his opinion, offer advantages commensurate with the time and enormous effort involved. He proposed instead, as a more economical course, a dual advance along the Luzon-Ryukyus and the Marianas-Bonins axes. He fully agreed with General MacArthur's plan to seize Luzon after Leyte. The seizure of Luzon would provide air and naval bases in the Philippines from which enemy shipping lanes in the China Sea could be blocked and, at the same time, Formosa effectively neutralized. From the ample bases in Luzon, it would be possible and desirable to seize positions in the Ryukyus for the prosecution of air operations against Kyushu and Honshu. The occupation of bases in the Bonins would open another route from the Marianas for bomber operations against Japan. The air assaults on Japan would culminate in landings on the enemy's home islands.{6}
Lt. Gen. Millard F. Harmon, Commanding General, U.S. Army Air Forces, Pacific Ocean Areas, in his reply to Admiral Nimitz referred to a previous letter which he had written to the Admiral, recommending, as an alternative to the invasion of Formosa and the China coast, the seizure of islands in the Ryukyu chain, for development as air bases from which to bomb Japan. He restated these views and emphasized his opinion that if the objective of CAUSEWAY was the acquisition of air bases it could be achieved with the least cost in men and materiel by the capture of positions in the Ryukyus.{7}
The commander of the ground troops designated for CAUSEWAY, Lt. Gen. Simon B. Buckner, Jr., Commanding General, Tenth Army, presented the primary objection to the entire Formosa operation. He informed Admiral Nimitz that the shortages of supporting and service troops in the Pacific Ocean Areas made CAUSEWAY unfeasible. General Buckner added, about a week later, that if an invasion of Luzon was planned the need for occupying Formosa was greatly diminished.{8}
Admiral Nimitz communicated the substance of these views to Admiral Ernest J. King, Commander in Chief, U.S. Fleet. The latter, who had been the chief proponent of an invasion of Formosa, proposed to the Joint Chiefs of Staff on 2 October 1944 that, in view of the lack of sufficient resources in the Pacific Ocean Areas for the execution of CAUSEWAY and the War Department's inability to make additional resources available before the end of the war in Europe, operations against Luzon, Iwo Jima, and the Ryukyus be undertaken successively, prior to the seizure of Formosa. Favorable developments in the Pacific and in Europe might make CAUSEWAY feasible at a later date.{9} On the next day, 3 October, the Joint Chiefs of Staff issued a directive to Admiral Nimitz to seize one or more positions in the Ryukyu Islands by 1 March 1945.{10} On 5 October Admiral Nimitz informed his command that the Formosa operation was now deferred and that, after General MacArthur invaded Luzon on 20 December 1944, the Pacific Ocean Areas forces would seize Iwo Jima on 20 January 1945 and positions in the Ryukyus on 1 March.{11}
The projected Ryukyus campaign was bound up strategically with the operations against Luzon and Iwo Jima; they were all calculated to maintain unremitting pressure against Japan and to effect the attrition of its military forces. The Luzon operation in December would allow the Southwest Pacific forces to continue on the offensive after taking Leyte. The occupation of Iwo Jima in January would follow through with another blow and provide a base for fighter support for the B-29's operating against Japan from the Marianas. The seizure of Okinawa in March would carry the war to the threshold of Japan, cut the enemy's air communications through the Ryukyus, and flank his sea communications to the south. Okinawa was, moreover, in the line of advance both to the China coast and to the Japanese home islands.{12}
Map No. 2 — Ryukyu Islands