Leapfrogging, also known as island hopping, was an amphibious military strategy employed by the Allies in the Pacific War against the Empire of Japan during World War II. The key idea was to bypass heavily fortified enemy islands instead of trying to capture every island in sequence en route to a final target. The reasoning was that those islands could simply be cut off from their supply chains (leading to their eventual capitulation) rather than needing to be overwhelmed by superior force, thus speeding up progress and reducing losses of troops and materiel.
As the 20th century dawned, the U.S. had several interests in the western Pacific to defend; namely, access to the Chinese market and its colonies – the Philippines and Guam – which the U.S. had gained as a result of the 1898 Spanish–American War. After Japan's victories in the Sino-Japanese War and the Russo-Japanese War, the U.S. began to regard Japan as a potential threat to its interests in the western Pacific. This antagonism was intensified by Japan's objections to an attempt to annex Hawaii to the U.S.[1] and by Japan's objections to discrimination against Japanese immigrants both in Hawaii[2] and California. As a result, as early as 1897 the U.S. Navy began to draft war plans against Japan, which were eventually codenamed "War Plan Orange". The war plan of 1911, which was drafted under Rear Admiral Raymond P. Rodgers, included an island-hopping strategy for approaching Japan.
After World War I, the Treaty of Versailles gave Japan a mandate over former German colonies in the western Pacific—specifically, the Mariana, Marshall, and the Caroline Islands. If these islands were fortified, Japan could in principle deny the U.S. access to its interests in the western Pacific. Therefore, in 1921, Major Earl Hancock Ellis of the U.S. Marine Corps drafted "Plan 712, Advanced Base Operations in Micronesia," a plan for war against Japan which updated War Plan Orange by incorporating modern military technology (submarines, aircraft, etc.) and which again included an island-hopping strategy.[3] Shortly afterward, a British reporter on naval affairs, Hector Charles Bywater, publicized the prospect of a Japanese-American war in his books Seapower in the Pacific (1921)[4] and The Great Pacific War (1925), which detailed an island-hopping strategy. The books were read not only by Americans but by senior officers of the Imperial Japanese Navy,[5] who used "island-hopping" in their successful southeast Asia offensives in 1941 and 1942.[6]
This strategy was possible in part because the Allies used submarine and air attacks to blockade and isolate Japanese bases, weakening their garrisons and reducing the Japanese ability to resupply and reinforce them. Thus troops on islands which had been bypassed, such as the major base at Rabaul, were useless to the Japanese war effort and left to "wither on the vine". General Douglas MacArthur greatly supported this strategy in his effort to regain the Philippines from Japanese occupation. This strategy began to be implemented in late 1943 in Operation Cartwheel. While MacArthur claimed to have invented the strategy, it initially came out of the Navy. While this strategy pre-dated World War II by many decades, MacArthur was the first Allied theater commander to practice this during the Allied offensive in the Pacific Theater.
MacArthur's Operation Cartwheel, Operation Reckless and Operation Persecution were the first successful Allied practices of leapfrogging in terms of landing on lightly guarded beaches and very low casualties but cutting off Japanese troops hundreds of miles away from their supply routes. MacArthur said his version of leapfrogging was different from what he called island hopping, which was the style favored by the Central Pacific Area commanded by Admiral Chester Nimitz that favored direct assaults on heavily defended beaches and islands leading to massive casualties for such small parcels of land like at Tarawa, Peleliu, Saipan, Guam, Iwo Jima, and Okinawa. MacArthur worked together with Admiral William Halsey, commander of the South Pacific Area but subordinate to MacArthur in Operation Cartwheel, in perfecting leapfrogging.[7]
MacArthur explained his and Halsey's strategy:
Leapfrogging would allow the United States forces to reach Japan quickly and not expend the time, manpower, and supplies to capture every Japanese-held island on the way. It would give the Allies the advantage of surprise and keep the Japanese off balance. The overall leapfrogging strategy would involve two prongs. A force led by Nimitz, with a smaller land force and larger fleet, would advance north towards the island and capture the Gilbert and Marshall Islands and the Marianas, going generally in the direction of the Bonin Islands. The southern prong, led by MacArthur and with larger land forces, would take the Solomon Islands, New Guinea, the Bismarck Archipelago, advancing toward the Philippines.
The bypassed Japanese forces were expected to be ineffective and "wither on the vine" and starve within a few months, but this did not occur. They cultivated gardens using seeds and equipment imported by aircraft and submarines and worked with local labor, and remained strong and well-organized. They remained capable of offensive action, and mounted major counterattacks against the American forces in the Battle of Driniumor River and the Bougainville counterattack. Containing these Japanese forces tied up six American divisions, threatening to make the American Army the one that became strategically ineffective. They did not pursue defeated Japanese forces and engaged in little patrolling beyond their defensive perimeters, allowing the defeated Japanese to regroup and reform. It also left local people at the mercy of the Japanese. When MacArthur returned to the Philippines, he abandoned leapfrogging in favor of a policy of the complete destruction of the Japanese forces, mainly based on a political imperative of liberating the Filipinos. Australian forces relieved the American garrisons in late 1944 and conducted offensives against the Japanese on Bougainville and at Aitape.