Preparations for the defense of the Philippines did not start in earnest until March 1944, when the IGHQ issued “Battle Preparations No. 11,” aimed to bolster the strength of the Fourteenth Army. The enemy landing at Hollandia in April 1944 finally convinced the IGHQ that no time must be lost in strengthening the defenses of the Philippines.
Defense Preparations, October 1943–June 1944
Between October 1943 and March 1944, the Japanese defense preparations in the Philippines were limited to preparing the islands as rear operational base for support of a decisive battle along the Marianas-Carolines–western New Guinea line. Yet the Japanese did not prepare any plan to reinforce the Philippines against an enemy invasion. One reason was that Japanese resources were already heavily taxed elsewhere. The Japanese also believed that the Allied advance could be stopped at the forward defense barrier before the Philippines were seriously threatened.
After the Japanese conquest of the Philippines in April 1942, the 24th Army, with four “mixed” (composite) brigades, was left as the occupying force. Its main task was to crush the growing guerrilla movement in the Philippines. In October 1943, the IGHQ directed the Fourteenth Army, responsible for the defense of the Philippines, to complete necessary base facilities by the spring of 1944. All the existing 13 airfields were scheduled for improvements, while an additional 30 airfields would be built. The plans also called for the expansion of other rear-area bases and communications routes.
The IGHQ directed additional personnel to the Philippines to accelerate the entire construction program. In late March 1944, the IGHQ’s Army section ordered a change of command organization for the southern area (put in effect on 5 April 1944). The Southern Army’s area of responsibility was enlarged to encompass deployment areas of the Fourteenth Army in the Philippines, the Second Army in western New Guinea and the eastern NEI and Fourth Air Army. The Fourteenth Army was directed to start defense preparations, with the focus on defense of Mindanao.
In April 1944, the commander of the Fourteenth Army, Lieutenant General Shigenori Kuroda, regrouped his forces to occupy better positions against the enemy’s possible invasion of the archipelago. The 16th Division (minus one infantry regiment), plus one independent mixed brigade and some other minor elements designated as Army reserve, was transferred from Luzon to Leyte. Two other brigades were deployed to northern and southern Luzon, respectively. The 30th Division, after its arrival from Korea in late April, was deployed to Mindanao.
By early May 1944, the Fourteenth Army consisted of only the 16th Division and four independent mixed brigades. The staff of the Fourteenth Army estimated that at least 15 divisions would be required to fight a decisive battle in the Philippines. However, because of the demands of reinforcing the Marianas–western New Guinea line there was little hope that these forces could be available for the defense of the Philippines.
Beginning in May 1944, the IGHQ relieved the Southern Army commander of all responsibility for the defense of eastern New Guinea. At the same time, the Eighteenth Army and other units were redeployed to new locations in western New Guinea. In mid-May, Field Marshal Terauchi transferred his headquarters to Manila to ensure more effective control over operations in that part of the theater. In addition, the 3rd Shipping Department HQ was relocated from Singapore to Manila.
During June 1944, approximately 15,000 to 20,000 additional Japanese troops were redeployed to the Philippines. The Fourteenth Army was directed to reorganize and increase each of its four independent mixed brigades to a division-size force. The new divisions were located at Davao (100th Division), Cebu (102nd Division), Baguio, Luzon (103rd Division), and Las Banos, Luzon (105th Division). In addition, two new brigades were activated in Luzon, while another newly organized brigade was transferred to Zamboanga (western Mindanao) via Cebu. Another brigade raised in Japan was also assigned to the Fourteenth Army. However, two out of the four newly created divisions lacked large unit training, and their recruits were poorly trained. Hence, teams of instructors were sent from Japan in June and July to help in training. Nevertheless, these brigades were not fully combat ready by the time of the enemy invasion of Leyte.
As part of their defense preparations, the Japanese also started a process of increasing reserves of logistical supplies for the Southern Army. The Southern Army’s Lines of Communications Command was established on 10 June. This headquarters consolidated the control of all transportation units in the Philippines and the logistical support for the Southern Army.
After the Japanese conquest of the Philippines, only small forces for local sea defenses were deployed in the archipelago. The main responsibility for naval defense of the Philippines belonged to the Southwest Area Force. Its area of responsibility stretched from central New Guinea in the east to Burma in the west. After July 1943, the Southwest Area Force HQ was temporarily in Penang, Malaya. It was moved back to Surabaya in February 1944. On 12 July, it was again relocated from Surabaya to Manila to assume closer control of naval bases and surface forces in the Philippine waters.
The 3rd Southern Expeditionary Fleet, subordinate to the Southwest Area Force, was specifically tasked for the defense of the sea approaches to the Philippines. In early May 1944, this fleet consisted of only ten, mostly small and obsolete vessels. All of them were involved in escort duties in the Philippine area.
In March 1944, the naval air strength in the Philippines consisted of the 32nd Air Group at Sarangani and the 31st Air Group at Nichols Field (Luzon). The Navy used only a dozen of airfields and seaplane bases in the archipelago. Initially these fields were used for pilot training, but later they were converted into frontline air bases. Sites for new airstrips were surveyed, especially at Davao and Manila areas, as additions to the Army’s airfields at Bagorod and the Clark Field area. Construction of the new and larger air bases progressed rapidly. An additional 21 naval air bases were planned for completion by the end of 1944.
The Japanese Navy did not concentrate its efforts on the defense of the Philippines until May 1944. Combined Fleet used the bases at Tawi-Tawi, Sulu Archipelago, and the Guimaras Strait in the Visayas. In March 1944, a decision was made to use Davao Bay as the main naval base in the southern part of the archipelago. New communications equipment was installed there because of the anticipated relocation of the Combined Fleet HQ from the western Carolines to Davao. It was also planned to move the First Air Fleet HQ from the Marianas to Davao. In mid-May 1944, the Combined Fleet arrived at Tawi-Tawi and spent about one month there before beginning its A-Operation, which led to the Battle of the Philippine Sea.
The Japanese recognized that the key factor in the successful defense of the Philippines would be air power. Consequently, the Battle Preparations No. 11 issued in March 1944 directed that the defense of Halmahera and the Philippines would be the responsibility of the air forces and assisted by Navy and ground forces. On the basis of the IGHQ’s assumption that the enemy would land on the Philippines in or after mid-November, training of the aircrews was scheduled for completion by the end of October.
The 4th Air Division directed the major part of the airfield construction. However, the Army troops would be mainly used for the construction. This, in turn, considerably affected their combat training and state of beach defenses. Construction of the airfields and aircraft shelters was completed by the end of September 1944.
At the beginning of 1944, the Japanese situation concerning land-based aircraft in the Philippines was extremely unsatisfactory. The 6th Air Division lost virtually all of its remaining aircraft in Hollandia. The 7th Air Division was fully committed in the defense of the island of Ceram, Moluccas. Operations in Burma prevented the Japanese from timely redeploying their aircraft to the defense of the Philippines if needed. Land-based naval air strength was limited to only the 26th Air Flotilla, redeployed from the Rabaul area to Davao in February 1944 for reorganization and training.
Shortly before issuance of Battle Preparations No. 11, the IGHQ’s Army section ordered the transfer of the 2nd and 4th Air Divisions from the Second Air Army in Manchuria to the Philippines. The 4th Air Division was directly assigned to the Fourth Air Army in late May, when the first increment of these reinforcements arrived in the Philippines. On 1 June, the Fourth Air Army HQ completed the planned transfer from Menado, Celebes, to Manila.
In April 1944, the Japanese Navy had in the Philippines only three air squadrons plus some training units. After the fall of the Marianas in July 1944, there was an urgent need to reconstitute naval air forces. The then newly organized Second Air Fleet was not employed in the Marianas because of its poor state of training. Its strength was gradually built up at its main basing area on Kyushu. The First Air Fleet was redeployed from Yap to Davao and then to the Clark airfield cluster. A plan to reconstitute that fleet encountered many obstacles because of enemy air strikes on its bases in September 1944. Also, the availability of aircraft had been severely reduced by maintenance difficulties and a lack of spare parts.
Allied advances in the spring and early summer of 1944 gave an increased urgency to prepare plans for the defense of Japan’s inner zone, the Philippines in particular. By late spring, the Japanese had concluded that the fate of the Philippines would determine the outcome of the struggle to defend the entire southern area. The Allied landing at Hollandia, which reportedly took the Japanese by surprise, reinforced their conviction that defenses in the Philippines had to be strengthened and the sooner the better.
Operational planning in the Japanese Army and the Navy was conducted by the respective general staffs and major field commands. The Army and Navy sections were organized along similar lines. The Army was a senior service, and, not surprisingly, its staffs were larger than the Navy’s. The Army section consisted of a number of “bureaus” or departments. The most important were the 1st (Operations), 2nd (Intelligence), 3rd (Transportation), and 4th (Communications) bureaus.
Operational plans were developed separately for each service in the 1st Bureau of the respective general staffs.20 Plans for a major operations prepared by the Army or the Navy were usually made without the input of the other service. Often, Army-Navy disagreement over a certain joint operation would result in the delay or even abandonment of the effort. Even when an agreement was reached, the operation would normally be executed not by a joint commander, but by respective service commanders. Unity of effort would be ensured by the terms of the pertinent Army-Navy Central Agreement.
The most important plans for the employment of Japanese naval forces normally originated within the IGHQ’s Navy section. The chief of the Navy section closely cooperated with the Navy Minister prior to the adoption of any operational plan. However, once the operation started, the Navy Minister did not have any direct or indirect control over operational matters.
The second highest planning echelon in the Navy was Combined Fleet HQ. The plans prepared at the Navy section and the Combined Fleet HQ were afterward elaborated in more detail by the numbered naval and air fleets, area fleets, and subordinate tactical commands. Within the Navy section, operational planning was the responsibility of the 1st Bureau’s 1st Section. Logistics planning was the responsibility of the 2nd Bureau. The 3rd Bureau provided intelligence, while all communications planning was the responsibility of the 4th Bureau. The Special Section of the 4th Bureau provided radio intelligence.
Final plans were prepared after discussion between the CINC, Combined Fleet, and the chief of the Navy section. Joint operations were discussed at the liaison conferences between the Army and the Navy, while the most important plans were discussed at the IGHQ. Agreement had to be reached with the Army section before a plan was submitted to the Chief of the Navy section for final approval. After a joint operation was agreed upon, the Navy and Army general staffs issued identical orders. If a joint plan involved the participation of other government agencies, then the Navy minister’s agreement had to be obtained. If a forthcoming operation exceeded the authority delegated by the Imperial Directive to the chief of the Navy section, the plan was submitted through the IGHQ to the emperor for approval. Afterward, the plan was issued as an order of the Navy section.
The Allies’ penetration of the New Guinea defense line and invasion of the Marianas convinced the IGHQ of the need to fight a decisive battle to protect the inner defense area. The Allies were advancing, and the Japanese expected them to attack the Philippines first. Simultaneously, they had to prepare contingency plans for the defense of Taiwan or Nansei Shoto, or possibly even Home Islands. The IGHQ’s basic order for the Sho-Go (Victory) operations was issued on 24 July 1944. The basic variants of the plan were as follows:
• Sho-1: Defense of the Philippines
• Sho-2: Defense of southern Kyushu, Nansei Shoto, and Taiwan
• Sho-3: Defense of Honshu and Shikoku, and, depending on the situation, the Ogasawara Group (Bonin Islands)
• Sho-4: Defense of the Hokkaido area
Broadly, the Sho plans were aimed at preventing the enemy from obtaining a foothold within the inner defensive perimeter running from Home Islands–Nansei Shoto–Taiwan–Philippines–Timor–Java–Sumatra. The basic strategic principle was that the IGHQ would designate as the “decisive battle area” whichever part of the inner defense area was attacked by the enemy’s main strength. Afterward, all available Japanese sea, air, and ground forces would be quickly concentrated to destroy the enemy forces. The prospective area of the “decisive battle” was Home Islands, Nansei Shoto, Taiwan, and the Philippines.
Sho-1’s strategic objective was to prevent the enemy’s forces from seizing control of the Philippine archipelago. The most important initial operational objective was to preclude enemy forces from obtaining a lodgment in the Philippines. The original Sho-1 plan, drafted in late July, envisioned a full-scale battle in Luzon fought with all three services, while naval and air forces would be primarily employed in defense of the central and southern Philippines.
The Japanese anticipated that the enemy’s possible (operational) objectives would be first to seize Mindanao, and then in decreasing order of probability, Leyte, San Bernardino Strait, and central Luzon. They believed that the best way to prevent the enemy from accomplishing his objectives would be to obtain command of the local sea area through a decisive defeat of enemy naval forces at the time of landing. Afterward, Japanese reinforcements could land without difficulty, enhancing prospects for a successful ground battle.
The Sho plans contained an “Outline of the Decisive Battle.” The IGHQ assumed that the enemy would apply the same amphibious landing scheme used in the invasion of the Marshalls, Hollandia, and Saipan. In all variants of the Sho plans, it was contemplated that the Second Air Fleet would provide the major part of the striking power for the decisive battle. In conducting the decisive battle, the initial priority would be to destroy enemy task forces (U.S. carrier groups), especially “regular” (fast) carriers. Afterward, the entire enemy invasion force would be destroyed in a single blow delivered by concerted efforts of the Japanese air, sea, and land forces. Attacks against the enemy carriers would be conducted predominantly at night and in bad weather. Attacks during daylight hours would aim to immobilize a large part of the enemy carrier force before the next night action, or to capitalize on the results of night attacks by mopping up any carriers that hadn’t already been sunk or crippled. Attacks on enemy transport convoys would be launched in daytime and aimed to reduce the strength of enemy landing forces before they hit the beaches.
The IGHQ’s outline of the decisive battle also envisaged the withdrawal and dispersal of the naval land-based aircraft in the face of the enemy air attacks before the enemy’s main landing. However, once enemy landing forces were engaged in the battle ashore, the naval land-based aircraft, cooperating with other naval forces and the Army air forces, would do their utmost to destroy those forces ashore.