Although Japan's fate in World War II was largely determined in the far reaches of the Pacific, for a generation preceding the war, the Imperial Japanese Army's leaders had not given much consideration to that area as a major theater of operations. Instead, they had directed their strategic and tactical preparations against their traditional enemy, Russia. Nazi Germany's invasion of the Soviet Union in June 1941 seemed like the golden opportunity for Japan to join its ally and destroy the weakened foe. But stinging defeats at the hands of the Red Army, particularly at Nomonhan in 1939, had left many imperial army leaders disinclined to attack the Soviets. Furthermore, the army was bogged down in China, where it had suffered 700,000 casualties since July 1937.
Senior Japanese Army officers initially dismissed the Pacific as a secondary theater and committed less than half the army's operational aircraft (1,500) and one-fifth of its personnel to the opening campaigns of the Pacific war. Eleven army divisions (of 51 total) and supporting units totaling 450,000 men attacked along a rim from Malaya to the Philippines. These units came from China, French Indochina, and Japan's Home Islands. The best formations, the prewar regular divisions stationed in Manchuria, remained there on alert against the Soviet threat.
Aggressive army doctrine translated into fast-moving, infantry-centered operations that overran British Malaya and drove Allied forces from Burma by May 1942. Simultaneously the army conquered the Netherlands East Indies and the Philippines and moved small numbers of troops into the Bismarcks, Papua New Guinea, the Marianas, and the Solomons. Japan's powerful navy, the strongest in the world after the Pearl Harbor attack, swept the seas of Allied warships, secured the army's line of communication to the southern regions, and provided air support as ground units fanned out across the Pacific. In exchange, the navy demanded ground troops to defend its far-flung conquests, and the unforeseen requirements overextended the army. Then Vice Chief of Staff Lieutenant General Tsukada Osamu likened the scattering of small army detachments throughout the Pacific to "sowing salt in the sea."
Japan's sensational string of victories during the initial stage of the war also masked fatal structural and institutional weakness in the military's command and control system. Interservice strategic and operational planning was almost nonexistent, and joint operations were ad hoc reactions to events. After the U.S. Marine Corps landing on Guadalcanal in August 1942, for example, the navy demanded army reinforcements to retake the island, but army general staff officers in Tokyo did not know where Guadalcanal was, much less that the navy had established a small base there.
Perhaps the confusion was understandable because the Pacific and the United States were afterthoughts in the Japanese Army's prewar strategic plans. The army could not force the U.S. Army into a decisive land battle and recognized that the American Army would soon recover from the loss of the Philippines in 1942. For the navy, however, the United States was the primary foe. Naval leaders aggressively pushed for further expansion into the Pacific to draw the U.S. Pacific Fleet into a decisive engagement, sink it, and make the western Pacific a Japanese lake.
Officers assigned to the army's general staff and war ministry well understood the enormous military potential of the United States, but estimated that the Americans would need at least two full years to bring that power to bear. During the interval, the army planned to erect an impregnable defensive barrier far from Japan's shores to conduct a protracted war of attrition that would prove too painful for the decadent Americans to endure. Otherwise there was no strategic or operational plan after the first six months of hostilities, no strategy for war termination, and no hope that the army could defeat the United States militarily.
Neither was the Japanese Army specially trained for jungle or island warfare. It remained a conventional, infantry-oriented force, indoctrinated with the spirit of the offensive and led at all echelons by aggressive commanders who relied on Japan's intangible qualities to overcome the material superiority of their foes. A few selected units received pre-Pearl Harbor jungle-warfare training and were equipped with tropical issue. Reinforcements and newly organized units were dispatched to the Pacific war zones without those benefits. Infantry tactics employed mobility, night movement, flanking attacks, and hand-to-hand fighting that proved readily adaptable to jungle combat. But an army structured for fast moving, large-unit operations was ill-suited for the island campaigns of the Pacific in which terrain fragmented large units and restricted maneuver. Doctrine also mandated resistance to the bitter end, stressed that captured territory could not be abandoned in the face of the enemy, and prohibited surrender.
Another major shortcoming was the army's lack of any counteramphibious doctrine. Instead, according to the Field Service Regulations, invaders would be met at the waterline, weakened on the beaches, and then counterattacked and destroyed. The suicidal banzai charges on Saipan in July 1944 illustrated the doctrine and its tenacious grip on Japanese tacticians. Only in mid-August 1944 did the high command issue a provisional tactical manual on island defense that called for hardened positions and a protracted defense. These were not static fortifications but strongpoints organized for a mobile defense executed with élan and fighting spirit. By that time, however, it was too late to change the embedded thinking of many Japanese officers who were determined to attack no matter what the circumstances.
Besides doctrinal shortcomings, the Japanese Army's culture hampered its performance. Line officers and operations staff officers were contemptuous of intelligence, which handicapped planning and operational effectiveness. Raw intelligence estimates badly underestimated the size of the U.S. Marine force on Guadalcanal, leading Colonel Kiyoano Ichiki to believe that his 600-man unit was conducting a reconnaissance-in-force against a numerically inferior opponent rather than an entire division. Army intelligence dismissed the loss of Tarawa in the Gilberts as a minor affair when it was the launching point for the U.S. Navy's Central Pacific offensive. Based on wildly exaggerated Japanese Navy claims during the Battle of Leyte Gulf in October 1944, intelligence reported that the U.S. Army forces on Leyte Island were about to surrender, and the army rushed reinforcements to a battle already lost.
Logisticians were held in even lower regard. It was evident before December 1941 that the army could not sustain units scattered across the Pacific and Asia. At an imperial liaison conference in November 1941, Army Chief of Staff General Sugiyama Hajime argued that if the navy maintained the sea-lanes, the army could defend the southern areas. More than a year earlier, however, the naval general staff's tabletop war games concluded that Japan could not keep the sea-lanes open. The navy minister ignored the outcome, and army leaders went along with the fiction.
Besides being overextended, army units were poorly supplied. Even before the start of the Pacific phase of Japan's wars, the army (which had its own water transport fleet) had agreed to release more than one million tons of shipping to keep the national economy and civilian sector afloat. Subsequent shipping shortages made it impossible to retake Guadalcanal, resupply forces on New Guinea, or fully reinforce the Central Pacific garrisons. To add to the burden, the army had a major commitment in China and conducted multidivision operations against British forces in Burma and India.
By April 1942, the army found itself defending advance bases that the navy needed in order to protect its major anchorages at Truk in the Caroline Islands, at Rabaul on New Britain, and in the Philippines. General Tsukada's nightmare had come true; the army was deployed in pennypackets throughout the vast Pacific. Once it was committed, its doctrine left commanders no choice except to hold the newly acquired ground.
After the U.S. Marines landed on Guadalcanal, the Japanese Army initially tried to retake the island. Counterattack after counterattack failed, but unwilling to give up territory, army leaders reinforced defeat and squandered precious resources. Only in late December 1942 did they decide to abandon Guadalcanal and then just temporarily to reconstitute in the northern Solomons, where they would prepare to retake the island. The army also continued offensive operations in Papua New Guinea until the destruction of the 51st Division convoy during the March 1943 Battle of the Bismarck Sea forced it to the strategic defensive.
In September 1943 the imperial army and navy agreed on an absolute defense zone stretching from the Kurile Islands to the Ogasawaras (Bonin Islands) and on to the Central Pacific, western New Guinea, Sumatra, and Burma. Behind this line Japan would construct a defensive network of island strongpoints and air bases to hurl back the American counteroffensive. But it would take about a year to build the fortifications and airfields required for the new strategy, and the U.S. onslaught never gave Japan the respite needed to complete its Pacific network.
The U.S. Navy's Central Pacific drive took the Marshall Islands in February 1944 and by July had reached the Marianas. At the same time, the U.S. Army leapfrogged over Japanese strongholds on New Guinea and was poised to liberate the Philippines. Despite setback after setback, Japanese Army commanders were reluctant to alter current doctrine. Officers at all echelons balked at shifting to purely defensive tactics.
Overstretched across the Pacific's vastness, the army was vulnerable to Allied air and submarine interdiction campaigns. Thousands of Japanese combat troops and tens of thousands of tons of equipment never reached their destinations. In addition to the 51st Division's destruction by American and Australian aircraft, U.S. submarines annihilated the 32nd and 35th divisions en route to reinforce western New Guinea in the spring of 1944. During the 3.5 months before the U.S. invasion of Saipan, the Japanese lost 200,000 tons of shipping laden with reinforcements and materiel bound for the Central Pacific front. At least 3,500 troops destined for Saipan never made it. As savage as the fighting during the Marianas campaign proved, it would have been far worse had the Japanese Army been able to move men, materiel, and supplies to the islands and erect solid, fully manned defenses before the U.S. invasion. American submarines and aircraft mauled Japanese resupply convoys bound for Leyte and Luzon in the Philippines, sinking transports carrying men and equipment of the 23rd and 16th Divisions. By early 1945, the danger posed by American submarines was so great that Imperial General Headquarters in Tokyo refused the Okinawa garrison's request for another division for fear it would fall victim to Allied submarines.
The Japanese Empire simply lacked the air and naval resources to sustain its far-flung garrisons. Cut off from reinforcements, Japanese defenders on the smaller islands where withdrawal inland was impossible—like Attu in the Aleutians, Tarawa, and Peleliu—went down fighting with suicidal fury. On the larger islands-Guadalcanal, New Guinea, Leyte, and Luzon-tactical withdrawals following defeats enabled the Japanese to fight on, but they retained their aggressive spirit and always looked for opportunities to attack. But only on Iwo Jima and Okinawa did they take advantage of the terrain and weaponry to fight protracted defensive battles of attrition that inflicted great damage on the attackers.
In the summer of 1945, army leaders in Tokyo confidently predicted success in the decisive battle of the homeland because for the first time in the war, the Americans would be fighting on an extended line of communication and could not isolate Japanese forces. The army had no hope of winning, but neither did it entertain any notion about surrendering without a fight. No one expected them to repel the invaders. The aim of homeland defense strategy was to inflict maximum casualties to compel the United States to agree to a negotiated settlement. It took two atomic bombs, the Soviet invasion in Manchuria, and the threat of an American invasion to convince Japanese Army leaders to surrender unconditionally.