Island-Hopping and Leap-frogging, U.S. Strategies Part I




After the Japanese attack on the U.S. naval facility at Pearl Harbor, Hawaii, in December 1941, the United States and its allies found themselves in a desperate strategic situation in the Pacific. In May 1942, elements of the U.S. Pacific Fleet turned back the Japanese threat to Australia in a strategic victory at the Battle of the Coral Sea. Even with another decisive victory at the Battle of Midway in June 1942, however, going on the offensive in the Pacific placed almost impossible demands on the limited resources of the United States and its allies, especially when Allied grand strategy emphasized the European theater of operations.

The U.S. leaders, General Douglas MacArthur and Admiral Chester Nimitz, dominated the Allies’ planning and operations in the Pacific war. Together with the joint chiefs of staff (JCS) in Washington, they adopted a two-pronged strategy divided between their respective areas of authority. MacArthur commanded the southwest Pacific theater and directed the southern prong of the Allied states, Australia and New Zealand. As the Pacific war progressed, MacArthur used Australia as a base of operations to drive through New Guinea and the Bismarck Islands in preparation for retaking the Philippines and eventually seizing Okinawa. From late 1942 through 1943, the Allied forces went on a slow, bloody offensive through the Solomon Islands and on New Guinea. Admiral Nimitz commanded the Pacific theater, which included the central, south, and north Pacific subdivisions. The northern prong of the Allied counteroffensive came under his control and struck westward across the central Pacific from the U.S. naval base at Pearl Harbor toward the Japanese home islands. Nimitz’s forces were made up almost exclusively of Americans. Little offensive activity occurred in his command until late 1943, when the U.S. Navy mustered a sufficient number of aircraft carriers to ensure U.S. air superiority.

Advancing in either the southwest Pacific or the central Pacific after the Battle of Midway in June 1942 required the Allies to attain several objectives. First, the U.S. Pacific Fleet needed to keep the Japanese Combined Fleet in check, if not totally destroy it. Second, Allied air superiority had to be established and maintained with both land- and carrier-based aircraft. Third, Allied forces needed to carry out repeated large-scale amphibious assaults. Finally, rolling back the Japanese forces meant attacking a strategic defense-in-depth in the Pacific, where island chains potentially served as mutually supporting bases of operations. To reach all these overlapping objectives, the Allies employed “island-hopping” and “leap-frogging” strategies to maximize limited resources, shorten time, and reduce casualties.

In theory, island-hopping made sense as a solution to cracking an island-based defense-in-depth. This strategy can be understood in the following example.

U.S. amphibious and naval forces successfully subdue a Japanese island base, X. In the following month or two, fresh troops replace the exhausted assault forces and crush any stubborn Japanese resistance. Then this island is used as a staging point for assaulting the next enemy-held island, Y. Seabees and army engineers speedily repair or construct airfields and dredge harbors as Allied forces mass for the next leg of the campaign.

Island X serves as air base, safe anchorage, and supply depot for the men and materiel being ferried from Australia or Hawaii. Fresh marine and army divisions receive their last-minute training before their amphibious assault on island Y with support from naval forces and aircraft based on island X. This strategy was employed during the Solomons campaign and later at Iwo Jima and Okinawa.

Island-hopping proved to be a strategic necessity early in the Pacific war. As 1942 drew to a close and 1943 began, the Allies could muster only limited carrier strength because of losses around Guadalcanal. At one point in October 1942, USS Enterprise was the only operational aircraft carrier in the theater, and it desperately needed an overhaul. Until the new Essex-class carriers became operational, amphibious attacks could not be supported beyond the range of land-based aircraft. Consequently, hopping from island to island under cover of aircraft from nearby bases was the only practical option.

As more carriers became available, U.S. leaders also used a leapfrogging strategy which entailed isolating, bypassing, or circumventing Japanese bases. In theory, leapfrogging was most practical when U.S. forces had achieved air and naval superiority. Without air or naval offensive capabilities, the leapfrogged Japanese forces became impotent because they could not attack U.S. forces or receive supplies or reinforcements. An example helps show how leapfrogging worked.

Three Japanese-held islands, A, B, and C, are situated roughly in a row; all have formidable defenses and some naval and airborne offensive capabilities. Allied air and amphibious forces begin by successfully subduing island A. Then this island becomes a staging point for supplies, men, and materiel for the next leg of the Allies’ campaign. Seabees and army engineers prepare an airfield and harbor for the forces massing on island A. Meanwhile, Allied land- and carrier-based aircraft attack and destroy the Japanese air and naval forces on island B, thus isolating the base and depriving its garrison of any offensive capability. Finally, when sufficient forces are available on island A, Allied forces leapfrog island B and strike at island C.

For Pacific commanders, leapfrogging was best explained with a baseball analogy: it was like “hitting ‘em where they ain’t.” The leapfrogged Japanese base was isolated in the rear area and left to “wither on the vine.” This strategy had two strategic benefits: U.S. forces could advance more quickly, and U.S. commanders could conserve their men and materiel. The leapfrogging strategy was employed at Rabaul, Truk, Mindanao, and the Caroline Islands.

Allied campaigns in the southwest and central Pacific alternated between hopping from island to island and leapfrogging an island. After the naval victories in the Battles of the Coral Sea and Midway earlier in 1942, the island-hopping strategy was used in New Guinea and the Solomon Islands from late 1942 into 1943. These islands were close to one another and thus easily lent themselves to island-hopping as well as base-hopping. Located near the southeastern tip of the Solomons, Guadalcanal was targeted as a primary strategic objective in Operation Watchtower, the Allies’ first offensive in the Pacific. For six months, the fighting on Guadalcanal raged as both the U.S. and Japan reinforced their land forces in a battle of attrition. On the island, the 1st Marine Division stubbornly held a defensive position around Henderson Field, the all-important air base for success in island-hopping.

Meanwhile, ongoing battles occurred in the air above and in the seas around Guadalcanal. Allied air-power and sea power gradually cut the Japanese supply lines and denied support to the enemy forces remaining on this island. Guadalcanal was under Allied control by the end of 1942. Allied forces then progressed to the northwest through the Solomon chain in a campaign to take the Japanese stronghold at Rabaul on the island of New Britain. To the southwest, MacArthur’s troops simultaneously moved over the Papuan peninsula of New Guinea. Together, operations on Guadalcanal and New Guinea served as preludes to a planned attack on Rabaul.

Located on New Britain in the Bismarck Archipelago, off the northern coast of New Guinea, Rabaul possessed powerful naval, air, and land forces which included more than 100,000 Japanese combatants. This base also controlled surrounding area and consequently blocked the Allied advance through the Solomons.

Initially, Rabaul was to be captured under Operation Cartwheel. However, at the Quebec Conference in August 1943, it became apparent that such an action would be much too costly in time, manpower, and materiel. The obvious solution was a modified Operation Cartwheel which called for leapfrogging or isolating Rabaul. In the battles that followed, Allied forces successfully encircled Rabaul by taking Bougainville, the Admiralty Islands, and other islands in the Bismarcks. Allied bombers and their fighter escorts traveled only 170 miles from Bougainville and pulverized the Japanese forces at Rabaul. After losing air and naval superiority, this base’s offensive capabilities and its threat to the continued Allied advance were negligible. In addition, Allied prizes such as the Admiralties served as important staging points for future operations. Although ultimately a strategic success, leapfrogging Rabaul took more than seven months of hard fighting.

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.

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