As 1943 drew to a close, deployment of Essex-class aircraft carriers irreversibly tipped the scales of air power in favor of the United States and enabled Admiral Nimitz’s central Pacific offensive, code-named Granite, to progress in earnest. Carrier-based air superiority conveyed two fringe benefits: strategic mobility and relative naval supremacy. With carrier-based aircraft, Nimitz therefore had much greater strategic mobility. Conversely, without adequate air cover, the Imperial Japanese Navy’s effectiveness was greatly decreased because its transportation and communications were severely limited.
Nimitz utilized the basic form of the War Plan Orange from the interwar years. Having appeared in various versions, this plan essentially called for the U.S. Pacific Fleet to fight its way across the central Pacific to relieve or recapture the Philippines. En route, the plan anticipated that the Orange (the color designation for Japan) fleet would be defeated in a decisive sea battle. Simultaneously, War Plan Orange anticipated that marine units would seize and defend “advanced bases” in Micronesia, more than a thousand islands stretching across the western Pacific approximately two thousand miles southwest of Hawaii.
Micronesia included the Gilbert, Marshall, Caroline, and the Mariana chains of islands and atolls. They rose out of coral or volcanic reefs and often amounted to no more than a few square miles. After being taken by U.S. forces, advanced bases in Micronesia were used to support subsequent operations. Consequently, the central Pacific strategy included not only island-hopping in a given island chain but also hopping from chain to chain.
Beginning in November 1943, U.S. carrier-based aircraft reduced Japanese air power in the Gilberts and screened the amphibious assault forces in case the Japanese navy contested U.S. landings. Anticipated counterattacks from Japanese bombers based in the Marshalls did not occur. More than 108,000 men in the U.S. Fifth Fleet and 5th Amphibious Corps focused on strong points in the Gilberts, such as Makin and Tarawa. Makin was relatively easy to subdue. Tarawa, however, proved to be more difficult; marines met its fanatical Japanese defenders on the beach. Taking this island was necessary because it provided needed practice in the complex combined arms operations of amphibious warfare: air and sea bombardments had to coordinate with amphibious landings. Tarawa’s airfield was also needed to a lesser extent for bombing operations against the Marshalls, a larger island chain 600 miles to the northwest.
The Marshalls stood next in line, and capturing them had several strategic benefits. The most important islands were Kwajalein and Eniwetok, both of which had airfields and naval anchorages. Japanese forces used Kwajalein as a logistics and communications hub for the rest of the Marshalls as well as the Gilberts. Eniwetok was an atoll which formed a natural harbor and could provide protection for major surface vessels. Neither island was defended by significant numbers of Japanese troops. Although the fighting was bloody, the Marshalls were quickly subdued by February 1944, within three months of the start of the central Pacific drive. After the Marshalls were taken, they formed the base of operations for the planned conquest of the Carolines. The navy refurbished and expanded the base at Eniwetok, which functioned as an advanced fleet anchorage for U.S. major combat vessels. Having such a base more than two thousand miles from Pearl Harbor proved invaluable to the next step in the central Pacific campaign. Aircraft from Eniwetok flew sorties against Wake Island and Truk in the Carolines.
Rather than continuing to hop from Marshalls to the Carolines to the Marianas, Nimitz decided on a two-stage maneuver in Operation Forager: first, leapfrog the Carolines, then seize the Marianas. The Micronesian island chains are not in a straight line, and the Carolines represented a formidable obstacle flanking the Marianas to the northwest and New Guinea to the south. Japanese naval and air forces at Truk in the Carolines presented the most significant threat to the Allied campaign; this base potentially blocked advances in both the central Pacific and the southwest Pacific. Dubbed the “Gibraltar of the Pacific,” Truk’s main island served as a major headquarters and base for the Japanese Combined Fleet where vessels like the super battleship Musashi were stationed. The U.S. Pacific Fleet leapfrogged the Carolines when U.S. air attacks from carriers and Eniwetok devastated the Japanese forces at Truk. The Japanese Combined Fleet fled, and U.S. aircraft destroyed most of Truk’s aircraft on the ground.
With Truk’s threat effectively neutralized, the second stage of Operation Forager went forward. It rivaled Allied operations in Europe and the Mediterranean Sea in vastness and complexity. The U.S. Fifth Fleet included 535 combat and auxiliary vessels which carried more than 127,500 troops, two-thirds of whom were marines. This armada was a self-sufficient expeditionary force. The logistical challenges of Operation Forager appeared almost insurmountable; the Fifth Fleet sailed more than a thousand miles from Eniwetok to the Marianas, where it conducted an amphibious assault against several Japanese-held islands. If that was not enough, U.S. planners fully expected that attacking the Marianas would draw a counterattack by the Imperial Japanese Navy. Nevertheless, Operation Forager was a success in part because of good planning and effective leadership.
In the Mariana Islands, amphibious assaults on Saipan, Tinian, and Guam occurred during the summer of 1944. Desperate Japanese defenders did not yield the Marianas without inflicting heavy casualties on U.S. forces. However, despite the cost in lives at the tactical level, leapfrogging the Carolines and securing the Marianas paid off handsomely at the strategic level. First, much time and many lives were saved overall. In addition, Allied occupation of these islands cracked Japan’s inner defensive perimeter and thus opened a way for Nimitz’s forces to converge on the Philippines and link up with MacArthur. Likewise, the strongly defended island of Iwo Jima was a short hop from the Marianas.
In 1944, another benefit became clear as the B-29 Superfortresses were deployed in the Pacific. With this aircraft’s exceptionally long range and with less then 1,300 miles between the Marianas and the Japan home islands, B-29s could bombard the heart of the shrinking Empire of the Rising Sun. Last, the Japanese regarded Saipan as part of their home territory, and thus losing the island was not only a strategic but also a morale blow.
As the central Pacific drive moved through Micronesia and secured the Marianas, MacArthur’s forces had been moving quickly along the northern coast of New Guinea during mid-1944. The Japanese base at Wewak was leapfrogged, and Hollandia was subsequently attacked. The once formidable Hollandia fell quickly after a heavy air bombardment, and its airfields in turn supported base-hopping operations against Wakde, Biak, Noemfoor, and Sansapor. By July 1944, three months after the initial isolation of Wewak, MacArthur and his forces controlled New Guinea and began preparing for an invasion of Mindanao and other islands of the Philippines.
In mid-1944, a debate raged among MacArthur, Nimitz, and the JCS. The Allies had to choose between two strategic options: leapfrog the Philippines as a whole and capture Formosa (now Taiwan), off the coast of China, or invade and subdue the Philippines. Chief of Naval Operations Ernest J. King and the JCS favored the first option. To them, it offered grand strategic benefits because the Philippines could be bypassed, and because Formosa could be used as the final stepping-stone for an invasion of Okinawa and the Japanese home islands. Conversely, the second option entailed a potentially lengthy operation to subdue the 7,000-island archipelago. MacArthur insisted on making good on his promise to return to the Philippines, and in the end he would not be denied. Nimitz also argued for an invasion of the Philippines to establish bases for operations against Japan itself. President Franklin D. Roosevelt intervened and ended the debate by mandating an invasion of the Philippines.
It should be noted that logistics and timetables played critical roles in the decision to capture the Philippines instead of Formosa. Planners expected that the assault on Formosa would require nine divisions. Such an operation was possible only in early 1945, when sufficient manpower became available. So, in the case of the Philippines, the leapfrogging strategy was rejected for the same reasons usually cited as benefits.
Once the invasion of the Philippines commenced in October 1944, both island-hopping and leapfrogging were employed in the campaign. Airfields were constructed after advances had been consolidated, and they supported the next phases of the operations. U.S. naval forces fought a series of battles with the remains of the Japanese Combined Fleet to retain air and naval superiority, despite some potentially disastrous mishaps and repeated kamikaze raids. The best example of leapfrogging in the Philippines was bypassing of the large island of Mindanao in the south part of the archipelago; instead, MacArthur’s forces attacked Leyte. After securing Mindoro as a base for aircraft, MacArthur then used an island hopping strategy by invading Luzon, which was brought under practical Allied control early in 1945.
With the most important Philippines islands as staging areas, the largest Allied armada in World War II made the hop from the Philippines to Okinawa in April 1945. After two months of some of the war’s bloodiest fighting, Okinawa fell. Not even a suicide mission by Yamato, Japan’s remaining superbattleship, could change the outcome. By the late summer of 1945, the invasion of southern Japanese home islands was expected to be launched from Okinawa—the last and most dreaded island-hopping operation.
Because of the “Europe-First” grand strategy in World War II, limited resources were available to the Allies in the Pacific. Only enough men and materiel were available for relatively small operations. Islandhopping and leapfrogging constituted a means to build several small steps into a large advance. This can be seen in the New Guinea, Philippines, and central Pacific campaigns. Moreover, using both island-hopping and leapfrogging in the two-pronged (southwest and central Pacific campaigns) strategy consistently kept the Japanese off balance. Also, hundreds of thousands of Japanese troops were tied down in the China-Burma-India theater. As a result, the Japanese were never able to take full advantage of their interior lines of communication and transportation because they had lost air, and consequently naval, superiority. They never concentrated their forces sufficiently to deal a deadly blow to either Allied advance, thus making their defeat all but inevitable.
FURTHER READINGS Isely, Jeter A., and Philip A.Crowl. The U.S. Marines and Amphibious Warfare: Its Theory and Practice in the Pacific (1951). MacArthur, Douglas. Reminiscences (1964). Miller, Edward S. War Plan Orange: The U.S. Strategy to Defeat Japan, 1897–1945 (1991). Morison, Samuel Eliot. The Two-Ocean War: A Short His-tory of the United States Navy in the Second World War (1963). Nimitz, Chester, and E.B.Potter. The Great Sea War (1960). Spector, Ronald H. Eagle Against the Sun: The American War with Japan (1985). U.S. Army. The War in the Pacific, 11 vols. In the series The United States Army in World War II (1948–1962). U.S. Marine Corps. History of U.S. Marine Corps Operations in World War II, 5 vols. (1958–1968). Weinberg, Gerhard L. “Grand Strategy in the Pacific War.” Air Power History (Spring 1996).