The Japanese plan for the occupation of the Philippines was but part of the larger plan for the Greater East Asia War in which the Southern Army was to seize Malaya and the Netherlands Indies while the Combined Fleet neutralized the U.S. Pacific Fleet. The Southern Army was organized on 6 November 1941, with General Count Hisaichi Terauchi, who had been War Minister in 1936, as commander.
His orders from Imperial General Headquarters were to prepare for operations in the event that negotiations with the United States failed. Under his command were placed the 14th, 15th, 16th and 25th Armies, comprising ten divisions and three mixed brigades. Southern Army’s mission in case of war would be to seize American, British, and Dutch possessions in the “southern area” in the shortest time possible. Operations against the Philippines and British Malaya were to begin simultaneously, on orders from Imperial General Headquarters. [Southern Army Opns, p. 6. The operations order given by the commander of the Southern Army was destroyed by fire. Certificate of Yozo Miyama, 1st Demob Bureau, Defense Doc 2726, IMTFE.]
Southern Army immediately began to prepare plans for seizure of the southern area. To 14th Army, consisting of the 16th and 48th Divisions and the 65th Brigade, was assigned the task of taking the Philippine Islands. The campaign in the East Indies was to be under the control of 16th Army; the 15th Army would take Thailand. The 25th Army was assigned the most important and difficult mission, the conquest of Malaya and Singapore, and was accordingly given four of the Southern Army’s ten divisions. Air support for these operations was to be provided by two air groups and an independent air unit. The 5th Air Group was assigned to the Philippine Campaign. [The Southern Army Opns, pp. 4-6. An air group was roughly the equivalent of a U.S. numbered air force, and was the largest tactical unit in the Japanese Army Air Force at that time.]
Beginning on 10 November a number of meetings attended by the senior army and navy commanders were held in Tokyo to settle various details in the execution of the plans. The commanders of the 14th, 16th, and 25th Armies, in session with the Premier (who was also the War Minister), the Army Chief of Staff, and General Terauchi, were shown the Imperial General Headquarters operational plans, given an outline of the strategy, and told what their missions would be in the event of war. In the discussions between Army and Navy commanders that followed this meeting a few modifications were made in the general strategy and the specific operational plans. Southern Army published its orders for the forthcoming operations, omitting only the date when hostilities would start.
Specific plans for the seizure of the Philippine Islands were first developed by the Japanese Army’s General Staff in the fall of 1941. As the plans for the southern area were developed, the Philippine plan was modified to conform to the larger strategy being developed and to release some of the forces originally assigned 14th Army to other, more critical operations. The final plan was completed at the meetings between the 14th Army commander, Lieutenant General Masaharu Homma, and the commanders of the 5th Air Group (Lieutenant General Hideyoshi Obata), the 3d Fleet (Vice Admiral Ibo Takahashi), and the 11th Air Fleet (Vice Admiral Nishizo Tsukahara), held at Iwakuni in southern Honshu from the 13th to the 15th of November.
The general scheme of operations for the Philippine campaign called for simultaneous air attacks starting on X Day, the first day of war, against American aircraft and installations in the Philippines by the 5th Air Group (Army) and the 11th Air Fleet (Navy). While the air attacks were in progress, advance Army and Navy units were to land on Batan Island, north of Luzon; at three places on Luzon: Aparri, Vigan, and Legaspi; and at Davao in Mindanao. The purpose of these landings was to seize airfields. The air force was to move to these fields as soon as possible and continue the destruction of the American air and naval forces from these close-in bases.
When the major part of American air strength had been eliminated, the main force of the 14th Army was to land along Lingayen Gulf, north of Manila, while another force would land at Lamon Bay, southeast of the capital. These forces, with close air support, were to advance on Manila from the north and south. It was expected that the decisive engagement of the campaign would be fought around Manila. Once the capital was taken, the islands defending the entrance to Manila Bay were to be captured and Luzon occupied.
Imperial General Headquarters and Southern Army expected General Homma to complete his mission in about fifty days; at the end of that time, approximately half of the 14th Army, as well as the Army and Navy air units, were to leave the Philippines for operations in the south. The remaining elements of the 14th Army were then to occupy the Visayas and Mindanao as rapidly as possible. Little difficulty was expected in this phase of the operations and detailed plans were to be made at the appropriate time. The Japanese considered it essential to the success of Southern Army operations to gain complete victory in the Philippines before the end of March 1942.
[Ibid., pp. 6-8; 14th Army Opns, I, 14. Unless otherwise specified, this account of the 14th Army’s plan for the conquest of the Philippines is taken from the 14th Army Opns, I and II. The translation has been checked against the original Japanese study prepared by the 1st Demob Bureau. Statement of Colonel Hattori, 2 Nov 47, ATIS Doc 49125, Statements of Japanese Officials on World War II, GHQ FEC, Mil Intel Sec, IV, 315.]
Forces assigned to the Philippine campaign, small as they were, were required in other more vital areas. The Japanese plan was based on a detailed knowledge of the Philippine Islands and a fairly accurate estimate of American and Philippine forces. The Japanese were aware that the bulk of the American and Philippine forces was on Luzon and that the U.S. Army garrison had been increased since July 1941 from 12,000 to 22,000.
Eighty percent of the officers and 40 percent of the enlisted men were thought to be Americans and the rest, Filipinos. American troops were regarded as good soldiers, but inclined to deteriorate physically and mentally in a tropical climate. The Filipino, though inured to the tropics, had little endurance or sense of responsibility, the Japanese believed, and was markedly inferior to the American as a soldier. The American garrison was correctly supposed to be organized into one division, an air unit, and a “fortress unit” (Harbor Defenses of Manila and Subic Bays). The division was mistakenly thought to consist of two infantry brigades, a field artillery brigade, and supporting services. The Japanese knew that MacArthur also had one battalion of fifty-four tanks-which was true at that time-and believed that there was also an antitank battalion in the Islands. The harbor defenses were known to consist of four coast artillery regiments, including one antiaircraft regiment.
The Japanese estimated that the American air force in the Philippines was composed of one pursuit regiment of 108 planes, one bombardment regiment of about 38 planes, one pursuit squadron of 27 planes, and two reconnaissance squadrons of 13 planes. American aircraft were based on two major fields on Luzon, the Japanese believed. They placed the pursuit group at Nichols Field, in the suburbs of Manila, and the bombers at Clark Field. Other fields on Luzon were thought to base a total of 20 planes. The Japanese placed 52 Navy patrol and carrier-based fighter planes at Cavite and 18 PBY’s at Olongapo.
The strength of the Philippine Army and the Constabulary, the Japanese estimated, was 110,000 men. This strength, they thought, would be increased to 125,000 by December. The bulk of the Philippine Army, organized into ten divisions, was known to consist mostly of infantry with only a few engineer and artillery units. This army was considered very much inferior to the U.S. Regular Army in equipment, training, and fighting qualities.
Though they had a good picture of the defending force, Japanese knowledge of American defense plans was faulty. They expected that the Philippine garrison would make its last stand around Manila and when defeated there would scatter and be easily mopped up. No preparation was made for an American withdrawal to the Bataan peninsula. In October, at a meeting of the 14th Army staff officers in Tokyo, Homma’s chief of staff, Lieutenant General Masami Maeda, had raised the possibility of a withdrawal to Bataan. Despite his protests, the subject was quickly dropped.
[Staff officers of the Interrog of General Maeda, 10 May 47, Mil Hist Div, GHQ FEC; statement of General Maeda, 2 Mar 50, ATIS Doc 56234; statement of Lieutenant Colonel Yoshio Nakajima, 6 Feb 50, ATIS Doc 56349; statement of Lieutenant Colonel Monjiro Akiyama, 2 Mar 50, A TIS Doc 56232; statement of Lieutenant Colonel Hikaru Haba, 2 Mar 50, ATIS Doc 56233; statement of Colonel Motoo Nakayama, 21 Mar 50, ATIS Doc 56640. Colonel Nakajima was, at the beginning of the Philippine Campaign, Intelligence Officer, 14th Army, and subsequently its Operations Officer. When Colonel Nakajima was made Operations Officer, Colonel Haba, formerly Assistant Intelligence Officer, 14th Army, was promoted to Intelligence Officer. Colonel Akiyama was 14th Army Air Officer, and Colonel Nakayama, Senior Operations Officer, 14th Army. Copies of these ATIS documents and interrogations are in Interrogations of Former Japanese Officers, Mil Hist Div, GHQ FEC, I and II.]
48th Division also claimed to have discussed the question of Bataan before the division embarked at Formosa. The consensus then was that while resistance could be expected before Manila and on Corregidor, Bataan “being a simple, outlying position, would fall quickly.”
The Japanese originally planned to assign to the Philippine campaign six battalions for the advance landings, two full divisions for the main landings, and supporting troops. So meager were the forces available to Southern Army that General Homma was finally allotted for the entire operation only 2 divisions, the 16th and 48th. Supporting troops included 2 tank regiments, 2 regiments and 1 battalion of medium artillery, 3 engineer regiments, 5 antiaircraft battalions, and a large number of service units. Once Luzon had been secured, most of the air units and the 48th Division, as well as other units, were to be transferred to the Indies and Malaya. At that time Homma would receive the 65th Brigade to mop up remaining resistance and to garrison Luzon. The 16th Division would then move south and occupy the Visayas and Mindanao.
The 14th Army commander had also counted on having the support of a joint Army and Navy air force of 600 planes. But one of the two air brigades of the 5th Air Group and some of the naval air units originally destined for the Philippines were transferred to other operations. The addition of the 24th Air Regiment to the 5th Air Group at the last moment brought the combined air and naval strength committed. [Statement of Colonel Moriji Kawagoe, CofS 48th Div, 9 Mar 50, ATIS Doc 56354; statement of Major Makoto Nakahara, Opns Officer, 48th Div, 13 Max 50, ATIS Doc 56372, ibid. to the Philippine campaign to about 500 combat aircraft.]
Air and Naval Plans
Air operations against the Philippines would begin on the morning of X Day when planes of the Army’s 5th Air Group and the Navy’s 11th Air Fleet, would strike American air forces on Luzon. These attacks would continue until American air strength had been destroyed. For reasons of security, there was to be no aerial or submarine reconnaissance before the attack, except for high altitude aerial photographs of landing sites. [The material on naval plans is taken from Naval Operations in the Invasion of the Philippines, Japanese Studies in World War II, No. 13, 2d Demob Bureau, pp. 1-6. Like other studies in this series, it is filed in OCMH and has been checked against the original. Morison, Rising Sun in the Pacific, pp. 161-63, is useful for the organization of Japan’s naval forces. See also Combined Fleet Top Secret Operations Order 1, in Pearl Harbor Attack Hearings, Part 13, Exhibit 8, pp. 432-84.]
By arrangement between the Japanese Army and Navy commanders, Army air units were to operate north of the 16th degree of latitude, a line stretching across Luzon from Lingayen on the west coast to the San defonso Peninsula on the east. Naval air units were made responsible for the area south of this line, which included Clark Field, the vital Manila area, Cavite, and the harbor defenses. This line was determined by the range of Army and Navy aircraft. The Navy Zero fighters had the longer range and were therefore assigned missions in the Manila area. Carrier planes of the 4th Carrier Division, originally based at Palau, were to provide air support for the landings at Davao and Legaspi. [The 11th Air Fleet had originally planned to use carrier-based fighters to neutralize southern Luzon, but the pilots trained for this mission were transferred with their planes to the Pearl Harbor operation. During the fall of 1941 the improvement of the Zero fighters and the rapid advancement in pilot training made it possible to utilize land-based fighters on Formosa for long-distance sorties against Luzon.]
Once the advance units of 14th Army had landed and secured airfields, the main force of the 5th Air Group was to move up to the fields at Aparri, Laoag, and Vigan, while naval air units would base on the fields at Legaspi and Davao. The airfield near Aparri was mistakenly believed to be suitable for heavy bombers and the bulk of the 5th Air Group was ordered there. It was anticipated that the forward displacement of the air forces would be completed by the sixth or seventh day of operations. During this week a naval task force from the 3d Fleet was to provide protection for the convoys and carry out antisubmarine measures in the Formosa area and in Philippine waters.
Naval surface forces assigned to the Philippines operations were under the 3d Fleet. This fleet, commanded by Admiral Takahashi, was primarily an amphibious force with supporting cruisers and destroyers. Its principal mission was to support the landings in the Philippines by minelaying, reconnaissance, escorting the troops during the voyage to the targets, and protecting them during landing operations. No provisions was made for surface bombardment of shore objectives, presumably in the interests of secrecy.
Because of the many landings to be made at widely scattered points in the Philippine archipelago it was necessary to organize the 3d Fleet into numerous special task forces. For the landing on Batan Island the Third Surprise Attack Force of 1 destroyer, 4 torpedo boats, and other small craft was organized. The naval escort for the landing of the advance units on Luzon consisted of the First, Second, and Fourth Surprise Attack Force, each composed of 1 light cruiser, 6 or 7 destroyers, transports, and other auxiliary craft. The Legaspi Force (Fourth Surprise Attack Force) was to be staged at Palau, and since it could not be supported by the planes of the 11th Air Fleet it included the South Philippines Support Force, comprising the 4th Carrier Division and 2 seaplane carriers with 20 planes each. The units landing at Davao were to be covered by this same force.
To support the main landings Admiral Takahashi created the Close Cover Force, which he commanded directly, composed of 1 light and 2 heavy cruisers, and 2 converted seaplane tenders. Two battleships and 3 heavy cruisers from Vice Admiral Nobutake Kondo’s 2d Fleet, then operating in Malayan and East Indian waters, were also to support the landings, which would be additionally supported by 3 of the escort groups. The Lamon Bay Attack Group, in addition to 1 light cruiser and 6 destroyers, included 6 converted gunboats and 1 battalion of naval troops.
Concentration of Forces
Early in November the forces assigned to the Philippine campaign began to move to their designated jump-off points. The 5th Air Group arrived in southern Formosa from Manchuria during the latter part of the month. On 23 November two of the advance detachments stationed in Formosa boarded ship at Takao and sailed to Mako in the Pescadores. Between 27 November and 6 December the 48th Division (less detachments) concentrated at Mako, Takoa, and Kirun, and made final preparations for the coming invasion. The first units of the 16th Division sailed from Nagoya in Japan on 20 November, followed five days later by the remainder of the division. Part of this division concentrated at Palau and the main body at Amami Oshima in the Ryukyus. On 1 December, when General Romma established his command post at Takao, he received final instructions from Southern Army. Operations would begin on 8 December (Tokyo time).
SOURCE: The Fall Of The Philippines by Louis Morton (United States Army Center of Military History)
World War Two: Philippines (Prewar; Part 1-4C); Defense Plans WPO-3 “Orange”
World War Two: Philippines (Prewar (Part 1-4A); Japanese strategy for a war