Japan entered the SWPA in a quest for oil. Oil powered Japan's economy and its armed forces, and the U.S. embargo of oil had helped trigger the Japanese decision to go to war against the United States. Dependent on foreign oil imports and rapidly using up its stocks, Japan needed to secure oil, the absence of which would paralyze Japanese industry within a year and immobilize the fleet within two years. Oil resources in the Netherlands East Indies, Japanese leaders believed, would make Japan self-sufficient in that vital commodity.
Japanese Southern Army headquarters in Saigon in French Indochina supervised army operations from the Philippines south. Navy leaders, meanwhile, decided that U.S. airfields and fleet bases could not be tolerated on the flank of this advance. Japanese Lieutenant General Homma Masaharu's Fourteenth Army with two divisions invaded the Philippines beginning on 8 December 1941. U.S. resistance officially ended on 7 May 1942. Meanwhile, Lieutenant General Imamura Hitoshi's Sixteenth Army with three divisions invaded the Netherlands East Indies beginning on 20 December. Dutch resistance there ceased on 8 March.
The Japanese had only a marginal shipping capacity during the war. By May 1942, the Japanese were securing oil from the conquests, but the fleet was only using about 42 percent of its merchant tanker capacity. Iron, manganese, chrome, and copper awaited exploitation in the Philippines. The Japanese desperately needed bauxite from the Netherlands East Indies for aircraft aluminum. Nickel was available from the Celebes. Local Japanese commanders were inefficient at developing these resources, and what materials the Japanese did extract from Borneo, Java, and Sumatra encountered shipping bottlenecks.
As the Japanese pushed south, their navy engaged in several actions. The Battle of the Java Sea largely destroyed the American-British-Dutch-Australian (ABDA) fleet. The United States won a small victory against Japanese transports in the Battle of Makassar Strait. There was also a fight at Badung Strait, and the Allied cruisers Houston and Perth were destroyed in the Battle of Sunda Strait. The short-lived ABDA Command collapsed in early March 1942, and the Japanese breached the Malay Barrier.
The startling successes of their initial campaigns encouraged the Japanese navy leadership to propose that five divisions invade Australia. Shipping and logistics, however, posed insurmountable problems as Japan, already short of shipping capacity, had lost 700,000 tons of shipping—nearly 12 percent of total capacity—sunk or severely damaged in the first four months of war. The Japanese army had never considered operating in the SWPA and had not planned how to campaign over such a large area and with such extended lines of communications. Japanese army planners estimated that to capture Australia would require 12 divisions and 1.5 million tons of shipping. The Japanese did not have the military assets and resources for such an operation. Australia was simply one continent too far.
Rather than invade Australia, Imperial General Headquarters in Tokyo ordered six of the divisions that had participated in the southern operations back to the Japanese home islands, China, and Manchuria. Planners redirected their logistical effort to the northwest and west when they should have been building bases—especially air bases—and establishing and supplying garrisons in the south.
On 30 March 1942, the U.S. Joint Chiefs of Staff established the Southwest Pacific Area. General Douglas MacArthur received command. It succeeded the ABDA area formed on 15 January as well as the Australia–New Zealand Area (ANZAC) established at the end of January. The first priority was to strengthen lines of communications to Australia and to build up logistics and airpower. The air war here would be primarily land-based.
Japan landed troops on New Guinea in February and March 1942. Japan sought Port Moresby on the south coast as an air base, part of its campaign to cut the lines of communications to Australia and to deny the port as a base for Allied counterattacks. In the May 1942 Battle of the Coral Sea, the U.S. Navy deflected the Japanese seaborne invasion attempt. The Japanese then attempted to seize Port Moresby by land, crossing over the Owen Stanley Mountains. Australian forces fought a delaying action south toward Port Moresby that weakened the Japanese and ultimately halted this thrust. The Australians then drove the Japanese back to New Guinea's north coast. A Japanese landing at Milne Bay failed, boosting Allied morale.
On 2 July 1942, the U.S. Joint Chiefs of Staff ordered MacArthur to begin an offensive to clear the Japanese from New Guinea. This effort was limited by the availability of forces and because the Americans' army and navy were both constrained by the priority given to Europe. The long fight for Buna concluded in late January 1943. The Australians and Americans executed shore-to-shore and ship-to-shore operations up New Guinea's coast. Rabaul on New Britain was initially a target, but the Americans chose to bypass that major Japanese bastion, cutting it off from outside resupply.
Although progress was slow, the Allies kept the initiative, imposed a tremendous drain on Japanese resources, and prevented the Japanese from consolidating their conquests. Weather, disease, and inhospitable terrain inflicted heavy losses on all combatants in this theater, but especially on the Japanese. Particularly devastating to the Japanese was the loss of so many of their air assets, and the destruction of Japanese transports in the Battle of the Bismarck Sea gave Japan a stark warning of the precariousness of its position.
The Americans launched almost every operation so as to extend their air umbrella and logistics closer to the Philippines. The strategy of island-hopping, which made use of growing U.S. Navy strength in the theater, allowed U.S. forces to advance, yet bypass strong Japanese ground forces. Allied shipping constraints and a shortage of service troops were greater impediments to the advance than shortfalls in combat troops.
The SWPA was the location of one of two major U.S. offensives (comprising mainly land-based air and ground forces) aimed at Japan. The second location was the Central Pacific, in which the U.S. offensives comprised mainly carrier air and sea power. The Japanese had insufficient assets to meet both offensives and were often off balance as they tried to maneuver against the two. The Japanese were simultaneously heavily committed in Burma and China and had to maintain major forces in Manchuria as a check on potential action by the Soviet Union.
The American SWPA and Central Pacific offensives indirectly supported each other early in the campaigns and then directly supported one another as they converged at the Luzon-Formosa-China coast area. The speed, flexibility, and mass of the two Allied thrusts neutralized the defender's traditional advantage of interior lines of communications. Coordination between the U.S. Army and Navy of current and future operations was critically important.
The Japanese regarded campaigns in New Guinea as a means to delay their enemies, reduce enemies' resources, and gain time to reorganize for a counteroffensive. Rather than weakening the Allies, however, the campaigns here became a drain on Japanese manpower, ships, and aircraft. Allied airpower cleared Japanese from the air and sea. Nowhere did the Japanese stop the advance, nor could they sustain the attrition that went with it.
The vast majority of Japanese troop and logistics shipping occurred in SWPA waters. Oil moved north through these waters, and U.S. submarines attacked the vital Malaya/Netherlands East Indies–Japan line of communications. Japan lost half its cargo-carrying capacity in 1944 to air and submarine attacks. Critical oil and raw materials required for war production in the home islands were sent to the ocean bottom.
The Battle of the Philippine Sea in June 1944 largely destroyed what remained of Japanese naval aviation. Japanese navy leaders then developed plans for a decisive battle, depending on the avenue of the U.S. advance. When the Americans invaded the Philippines in October, the Japanese immediately initiated their plan, which resulted in the Battle of Leyte Gulf—the greatest naval battle, in terms of ships and numbers of men engaged, in history. In the ensuing battle, the U.S. Navy all but destroyed the Japanese navy as an organized fighting force.
The inability of Japan to transport men and supplies to Leyte and its similar difficulties in supplying and reinforcing Luzon hastened Japan's defeat in the Philippines. The U.S. conquest of the Philippines enabled U.S. airpower there to sever the seaborne supply lines between the Japanese home islands and its Southern Resource Area. U.S. Navy forces swept into the South China Sea in January 1945 and severed Japanese lines of communications with Indochina. The American conquest of the Philippines, the ability of carrier task forces to go wherever they pleased, and the strangulation wrought by the submarine fleet completely isolated the Southern Resource Area.
Large Japanese ground forces remained in Indochina and in the Netherlands East Indies, but they could play no role in defense of the home islands, nor could raw materials reach the home islands. This fact made MacArthur's use of Australian forces in Borneo in mid-1945 all the more questionable. It was a campaign with little strategic value.
The last operations in the SWPA were American preparations for the invasion of Japan. The Philippines provided staging areas for 18 U.S. Army divisions, large numbers of aircraft, logistics organizations, and hundreds of ships. With Japan's surrender in August, operations in the SWPA came to an end. The conclusion of hostilities did not bring peace, however, as wars in which indigenous peoples sought independence from their colonial occupiers soon began.
John W. Whitman
Bergerud, Eric. Touched with Fire: The Land Campaign in the South Pacific. New York: Penguin Books, 1996.; Bergerud, Eric. Fire in the Sky. The Air War in the South Pacific. Boulder, CO: Westview Press, 2000.; Craven, Wesley F., and James E. Cate, eds. The Army Air Forces in World War II. Vol. 1, Plans and Early Operations, January 1939 to August 1942. Chicago: Office of Air Force History, University of Chicago Press, 1948.; Hattori Takushiro. The Complete History of the Greater East Asia War. 4 vols. Trans. Headquarters, 500th Military Intelligence Service Group. Tokyo: Masu Publishing, 1953.; Morison, Samuel Eliot. History of United States Naval Operations in World War II. Vol. 5, The Struggle for Guadalcanal, August 1942–February 1943. Boston: Little, Brown, 1949.; Morton, Louis. United States Army in World War II. The War in the Pacific. Fall of the Philippines. Washington, DC: Office of the Chief of Military History, Department of the Army, 1953.