The 'Battle of the Philippine Islands' was the campaign in which Japanese forces took the Philippine islands group and defeated the Filipino and US forces seeking to hold them (8 December 1941/8 May 1942).

The Japanese launched the invasion by sea from Formosa, a large island more than 200 miles (320 km) to the north of the Philippine islands group. The defending forces outnumbered the Japanese by as ratio of about 3/2 but were a mixed force of non-combat experienced regular, national guard and constabulary formations and units as well as newly-created elements of the Commonwealth of the Philippines. The Japanese used first-line troops at the outset of the campaign, and by concentrating their forces swiftly overran most of Luzon island during the first campaign’s month.

The Japanese high command, believing that they had won the campaign, made a strategic decision to advance by a month their timetable of operations in Borneo and the Netherlands East Indies, and therefore withdrew their best division and the bulk of their air power at a time early in January 1942. In combination with the defenders' decision to withdraw into a defensive holding position in the Bataan peninsula and also the defeat of three Japanese battalions in the 'Battle of the Points' and the 'Battle of the Pockets', enabled the US and Filipino forces to hold out for another four months. After their failure to penetrate the Bataan defensive perimeter in February, the Japanese conducted a 40-day siege. The crucial large natural harbor and port facilities of Manila Bay were thus denied to the Japanese until May 1942. While the operations to take the Netherlands East Indies were unaffected, this severely hindered the Japanese offensive operations in New Guinea and the Solomon islands group, thereby providing the time for the US Navy to make plans to engage the Japanese on and round Guadalcanal instead of much farther to the east.

Japan’s conquest of the Philippine islands group is often considered as the worst military defeat in US history. About 23,000 US military personnel and about 100,000 Filipino soldiers were killed or taken prisoner.

The Japanese planned to occupy the Philippine islands group within their scheme for a 'Greater East Asia War' in which General Hisaichi Terauchi’s Southern Expeditionary Army Group seized sources of raw materials in Malaya and the Netherlands East Indies while Admiral Isoroku Yamamoto’s Combined Fleet neutralised the US Pacific Fleet. Five years earlier, in 1936, Captain Ishikawa Shingo, a hard-liner in the Japanese navy, had toured the Philippines and other parts of the South-East Asia, noting that these countries had abundant quantities of the raw materials Japan urgently needed for its armed forces, and this had helped to increase the Japanese aspiration for colonising the Philippine islands group.

The Southern Expeditionary Army Group was created on 6 November 1941 under the command of Terauchi, who had previously been minister of war. This major formation was ordered to prepare for war in the event that negotiations with the USA did not succeed in a peaceful solution of Japanese objectives. These objectives included the US acceptance of the Japanese position in the Pacific Ocean as a superior force, with the testament of their occupation of China, but the Japanese did not succeeded in gaining US approval. Under Terauchi’s command were four corps-equivalent armies, comprising 10 divisions and three combined-arms brigades, including Lieutenant General Masaharu Homma’s 14^th Army that was to undertake operations against the Philippine islands group and Malaya simultaneously when ordered by the Imperial General Headquarters.

The invasion of the Philippine islands group had four objectives: firstly, to prevent the Philippine islands group being developed an advance base for US forces; secondly, to acquire staging areas and supply bases to enhance operations against the Netherlands East Indies and Guam in the Marians islands group; thirdly, to secure the lines of communication between occupied areas in the south and the Japanese home islands; and fourthly, to limit the scope of Allied intervention when the Japanese attempted to launch offensive campaigns in Australia and the Solomon islands group through the despatch od all the forces stationed in the country and other neighbouring nations.

Terauchi assigned the Philippines invasion to the 14^th Army with air support Lieutenant General Hideyoshi Obata’s 5^th Air Group, which was transferred to Formosa from Manchuria. The amphibious invasion was conducted by Vice-Admiral Ibo Takahashi’s Philippines Force using the Imperial Japanese navy 3^rd Fleet supported by the land-based aircraft of Vice Admiral Nishiso Tsukahara’s 11^th Air Fleet.

The 14^th Army had two first-line infantry divisions, in the form of Lieutenant General Susuma Morioka’s 16^th Division and Lieutenant General Yuitsu Tsuchihashi’s 48^th Division, to land on and take Luzon, the single most important part of the Philippines islands group, and Major General Naka Akira’s 65^th Brigade as a garrison force.  The Formosa-based 48^th Division, though lacking combat experience, was considered one of the Japanese army’s best formations, was specially trained for amphibious operations, and was given the assignment of the main landing in Lingayen Gulf. The 16^th Division, assigned to land at Lamon Bay, was picked as one of the best divisions still available in Japan itself and staged from the Ryukyu and Palau island groups. The 14^th Army also had the 4^th and 7^th Tank Regiments, five field artillery battalions, five anti-aircraft artillery battalions, four anti-tank companies, and one mortar battalion. An unusually strong group of combat engineer and bridging units was included in the 14^th Army's support forces.

For the invasion, the 3^rd Fleet was augmented by two destroyer squadrons and one cruiser division of the 2^nd Fleet, and the aircraft carrier Ryujo from the 1^st Air Fleet. The Philippines Force comprised one aircraft carrier, five heavy cruisers, five light cruisers, 29 destroyers, two seaplane tenders, minesweepers and torpedo boats.

The combined army and navy air strength allocated to support the landings was 541 aircraft. The 11^th Kokukantai (air fleet) consisted of the 21^st and 23^rd Kokusentai (air flotillas), a combined strength of 156 Mitsubishi G4M 'Betty' and Mitsubishi G3M 'Nell' twin-engined medium bombers, 107 Mitsubishi A6M Reisen 'Zero' single-engined fighters and a number of seaplanes and reconnaissance aircraft. Most of these aircraft were based at Takao in south-western Formosa, and approximately one-third were sent to Indo-China in the last week of November to support operations in Malaya. The Ryujo provided an additional 16 fighters and 18 torpedo bombers, and the surface ships had 68 floatplanes for search and observation, totalling 412 naval aircraft. The army’s 5^th Kikoshidan (air group) comprised two fighter regiments, two light bomber regiments and one heavy bomber regiment, totalling 192 aircraft: these aircraft were 76 Mitsubishi Ki-21 'Sally' twin-engined, Kawasaki Ki-48 'Lily' twin-engined and Mitsubishi Ki-30 'Ann' single-engined bombers, 36 Nakajima Ki-27 'Nate' single-engined fighters, and 19 Mitsubishi Ki-15 'Babs' and Tachikawa Ki-36 'Ida' sinle-engined machines.

From mid-1941, following the increasing level of tension between Japan and several other powers, including the USA, ther UK and the Netherlands, many countries in South-East Asia and the Pacific began to prepare for the possibility of war. By December 1941, the combined defence forces in the Philippine islands group were organised into the US Army Forces in the Far East (USAFFE), which eventually included the Philippine army’s 1^st Regular Division, 2^nd (Constabulary) Division and 10 mobilised reserve divisions, and the US Army’s Philippine Department. General Douglas MacArthur was recalled from retirement by the US Department of War and named commander of the USAFFE on 26 July 1941. MacArthur had retired in 1937 after two years as military adviser to the Philippine Commonwealth, and accepted control of the Philippine army, tasked by the Filipino government with reforming an army made up primarily of reservists lacking equipment, training and organisation.

On 31 July 1941, the Philippine Department had 22,532 me, about half of them Filipinos. MacArthur recommended the reassignment of department commander, Major General George Grunert, in October 1941 and himself took command. The main component of the department was the US Army Philippine Division, a 10,500-man formation that comprised mostly Philippine Scouts combat units. The Philippine Department had been reinforced between August and November 1941 by 8,500 men oif the US Army Air Forces, and by three Army National Guard units, including its only armour in the form of two battalions of M3 light tanks. These units, the 200^th Coast Artillery Regiment (an anti-aircraft unit), the 192^nd Tank Battalion and the 194^th Tank Battalion were all based on men from New Mexico, Wisconsin, Illinois, Ohio, Kentucky, Minnesota, Missouri and California. After reinforcement, the department’s strength on 30 November was 31,095 men, including 11,988 Philippine Scouts.

MacArthur organised the USAFFE into four tactical commands. The North Luzon Force, activated 3 December under Major General Jonathan M. Wainwright, defended the most likely sites for amphibious attacks and the central plains of Luzon. Wainwright’s forces included the Philippine army’s 11^th, 21^st and 31^st Divisions, the US 26^th Cavalry Regiment (Philippine Scouts), one battalion of the 45^th Infantry (Philippine Scouts) and the 1^st Provisional Artillery Group of two batteries of 155-mm (6.1-in) guns and one 75-mm (2.95-in) mountain gun. The Philippine 71^st Division served as a reserve and could be committed only on the MacArthur’s authority.

The South Luzon Force, which was activated on 31 December under the command of Brigadier General George M. Parker, controlled a zone to the east and south of Manila. Parker had the Philippine army’s 41^st and 51^st Divisions, and the 2^nd Provisional Artillery Group of two batteries of the US 86^th Field Artillery (Philippine Scouts).

The Visayan-Mindanao Force under the command Brigadier General William F. Sharp, comprised the Philippine army’s 61^st, 81^st and 101^st Divisions, reinforced after the start of the war by the newly inducted 73^rd and 93^rd Regiments. The 61^st Division was located on Panay island, the 81^st Division on Cebu and Negros islands, and the 101^st Division on Mindanao island. In January a fourth formation, the 102^nd Division, was created on Mindanao island from the field artillery regiments of the 61^st and 81^st Divisions to serve as infantry as they had no pieces of artillery, and the 103^rd Regiment of the 101^st Division. The 2^nd Regiment of the Philippine army’s 1^st Regular Division and the US 2/43^rd Infantry (Philippine Scouts) were also made a part of the Mindanao Force.

The USAFFE’s Reserve Force, under MacArthur’s direct control, comprised the Philippine Division, the 91^st Division (Philippine Army), and headquarters units from the Philippine army and the Philippine Department, positioned just to the north of Manila. The 192^nd and 194^th Tank Battalions formed the separate Provisional Tank Group, which was also under MacArthur’s direct command, at Clark Field/Fort Stotsenburg, where they were positioned as a mobile defence against any attempt by airborne units to seize the field.

Four US Coast Artillery Corps regiments guarded the entrance to Manila Bay, including Corregidor island. Across a narrow 1.85-mile (3-km) strait of water from Bataan to Corregidor was Fort Mills, defended by batteries of the 59^th and 60^th Coast Artillery (the latter an anti-aircraft unit), and the 91^st and 92^nd Coast Artillery (Philippine Scouts) of the Harbor Defenses of Manila and Subic Bays. The 59^th Coast Artillery acted as a supervisory unit for the batteries of all units positioned on Forts Hughes, Drum, Frank and Wint. The majority of the forts had been built in the period between 1910 and 1915, and with the exception of of Fort Drum and Battery Monja on Corregidor, were unprotected against air and high-angle artillery attack except by camouflage.

The USAFFE’s aviation arm was Major General Lewis H. Brereton’s Far East Air Force of the USAAF. Previously the Philippine Department Air Force and Air Force USAFFE, the Far East Air Force was activated on 18 November, and was the largest USAAF combat air formation outside the USA. Its primary combat power in December 1941 consisted of 91 serviceable Curtiss P-40 Warhawk single-engined fighters and 34 Boeing B-17 Flying Fortress four-engined heavy bombers, with further modern aircraft in transit to the Philippine islands group. Tactically, the Far East Air Force was part of the Reserve Force, so that it fell under MacArthur’s direct command.

As of 30 November, the strength of the US Army in the Philippines islands group, including Philippine units, was 31,095 men in the form of 2,504 officers and 28,591 enlisted men (16,643 Americans and 11,957 Philippine Scouts).

MacArthur’s mobilisation plan called for induction of the 10 reserve divisions between 1 September and 15 December 1941. The timetable was met on 1 September with the induction of one regiment per division, but slowed as a lack of facilities and equipment hampered training. The divisions' second regiments were not called up until 1 November, and the third regiments were not organised until after the start of the Pacific War. Training was also seriously impeded by language difficulties between the US cadres and the Filipino troops, and by the many differing dialects (estimated at no fewer than 70) of the numerous ethnic groups comprising the army. By the outbreak of war, therefore, only two-thirds of the army had been mobilised, but additions to the force continued with the induction of the Philippine Constabulary and a portion of the regular army, until a force of approximately 130,000 men was reached.

The most critical equipment shortfalls were in rifles and divisional light artillery. MacArthur requested 84,500 M1 Garand semi-automatic rifles with which to replace the World War I M1917 Enfield bolt-action rifles then equipping the Philippine army, of which there were adequate numbers, but the Department of War denied this request as a result of production difficulties. The divisions had only 20% of their artillery requirements, and while plans had been approved for a major reduction of this gap, they were too late to be implemented before war isolated the Philippines islands group.

By contrast, the Philippine Division was adequately manned, equipped and trained. MacArthur received immediate approval to modernise it by reorganising it as a mobile 'triangular' division. Increasing the authorised size of the Philippine Scouts was not politically viable as a result of resentment within the more poorly paid Philippine army, so MacArthur’s plan also provided for the use of Philippine Scouts to round out other units. The transfer of the US 34^th Infantry from the 8^th Division in the USA to the Philippine Division, accompanied by two field artillery battalions to create a pair of complete regimental combat teams, was in progress as the war broke out. The deployment ended with the troops still in the USA, whence they were sent to defend the Hawaiian islnds group.

The US Asiatic Fleet and 16^th Naval District, based in Manila, provided the naval defence of the Philippine islands group. Commanded by Admiral Thomas C. Hart, the surface combatants of the Asiatic Fleet were the heavy cruiser Houston, the light cruiser Marblehead and 13 World War I-era destroyers. The Asiatic Fleet’s primary striking power lay in its modern submarines: Submarine Squadron 2 comprised 12 'Salmon' class submarines, and Submarine Squadron 5 of 11 'Porpoise' and 'Sargo' class submarines. In September 1941, the naval patrol forces in the Philippines were augmented by the arrival of the six PT-boats of Motor Torpedo Boat Squadron 3. Likewise, the gunboats of the China Yangtze Patrol also became part of the Philippine naval defenses: Asheville (sunk to the south of Java on 3 March 1942), Mindanao (lost on 2 May 1942), Luzon (scuttled on 6 May 1942 but salvaged by the Japanese), Oahu (sunk on 5 May 1942) and USS Quail (scuttled on 5 May 1942). In December 1941, the naval forces were augmented by the schooner Lanikai.

The 4^th Marine Regiment, stationed in Shanghai, China, since the late 1920s, had anticipated a withdrawal from China during the summer of 1941. As personnel were routinely transferred back to the USA or separated from the service, the regimental commander, Colonel Samuel L. Howard, arranged unofficially for all replacements to be placed in the 1^st Special Defense Battalion, based at Cavite. When the 4^th Marines arrived in the Philippine islands group on 30 November 1941, the regiment incorporated the marines at Cavite and Olongapo Naval Stations into its understrength ranks. An initial plan to divide the 4^th Marines into two regiments, mixing each with a battalion of Philippine Constabulary, was discarded after Howard expressed his reluctance, and the 4^th Marine were stationed on Corregidor island to augment the defences there, with details detached to Bataan to protect USAFFE headquarters.

Additionally the US Coast and Geodetic Survey, a paramilitary survey force, operated in Manila with the ship Research.

News of the Japanese 'Ai' attack on Pearl Harbor reached the Philippine islands group at 02.20 local time on 8 December 1941.Fighters of the Far East Air Force had already undertaken an air search for incoming aircraft reported shortly after 00.00, but these had been Japanese scout aircraft reporting weather conditions. At 03.30, Brigadier General Richard K. Sutherland, MacArthur’s chief-of-staff, heard about the attack from a commercial radio broadcast. At 05.00 Brereton reported to USAFFE headquarters, where he attempted unsuccessfully to see MacArthur, and therefore recommended to Sutherland, that the Far East Air Force launch bombing missions against Formosa in accordance with the 'Rainbow 5' war plan directives and from which an attack was likely to come. Brereton was further made aware of an attack against the destroyer William B. Preston in Davao Bay. Authorisation was refused, but shortly after this, and in response to a telegram from General George C. Marshall, the US Army chief-of-staff, instructing MacArthur to implement 'Rainbow 5', Brereton was ordered to have an attack force in readiness for later approval.

Through a series of disputed discussions and decisions, authorisation for the first raid was not approved until 10.15 for an attack just before sunset, with a follow-up raid at dawn on the following day. In the meantime, Japanese plans to attack Clark and Iba Fields using land-based naval bombers and A6M fighters were delayed for six hours by fog at the Formosa bases, so only a small-scale Japanese army mission attacked targets in the northern tip of Luzon. At 08.00, Brereton received a phone call from Arnold warning him not to allow his aircraft to be attacked on the ground. The Far East Air Force launched three squadron-sized fighter patrols and all of its serviceable bombers on Luzon between 08.00 and 08.30 as a precautionary move. After MacArthur had given Brereton the authorisation he sought at 10.15, the bombers were ordered to land and prepare for the afternoon’s raid on Formosa. All three fighter squadrons began to run short on fuel and broke off their patrols at the same time.

The 20^th Pursuit Squadron’s P-40B interceptors patrolled the area while the bombers landed at Clark Field between 10.30 and 10.45, then dispersed to their revetments for servicing and refuelling. The 17^th Pursuit Squadron, based at Nichols Field, also landed at Clark Field and had its aircraft refuelled while its pilots ate lunch, then put its pilots on alert shortly after 11.00. All but two of the B-17 bombers at Clark Field were on the ground.

At 11.27 and 11.29, the radar post at Iba Field detected two incoming raids while the closer was still some 130 miles (210 km) distant. The post alerted the headquarters of the Far East Air Force and the command post at Clark Field, a warning that reached only the pursuit group commander, Major Orrin L. Grover, who apparently became confused by multiple and conflicting reports. The 3^rd Pursuit Squadron took off from Iba Field at 11.45 with instructions to intercept the western force, which was thought to have Manila as its target, but dust problems during its take-off resulted in the fragmentation of its flights. Two flights of the 21^st Pursuit Squadron at Nichols Field, totalling six P-40E machines, took off at 11.45 and headed toward Clark Field before being diverted to Manila Bay as a second line of defence in the event that the 3^rd Pursuit Squadron failed to effect an interception. The 21^st Pursuit Squadron’s third flight, taking off five minutes later, headed toward Clark Field, although engine problems with its new P-40E fighters reduced its numbers by two. The 17^th Pursuit Squadron took off at 12.15 from Clark Field with orders to patrol over Bataan and Manila Bay, while the 34^th Pursuit Squadron at Del Carmen never received its orders to protect Clark Field, so none of its fighters took off. The 20^th Pursuit Squadron, dispersed at Clark Field, was ready to take-off but received no orders from group headquarters. Instead a line chief saw the incoming Japanese formation and the section commander ordered the aircraft to scramble.

Even though tracked by radar and with three US fighter squadrons in the air, when the bombers of the 11^th Kokukantai attacked Clark Field at 12.40 they achieved tactical surprise. Two squadrons of B-17 bombers were dispersed on the ground. Most of the P-40 fighters of the 20^th Pursuit Squadron were preparing to taxi and were struck by the first wave of 27 G3M 'Nell' bombers: only four of the 20^th Pursuit Squadron’s P-40B fighters managed to take-off as the bombs began to rain down on the airfield.

A second attack by 26 G4M 'Betty' bombers followed closely, then escorting A6M fighters strafed the field for 30 minutes, destroying 12 of the 17 US heavy bombers present and seriously damaging three others. Two damaged B-17 machines were made flyable and taken to Mindanao, where one of them was lost in a ground collision.

A near-simultaneous attack on the auxiliary field at Iba to the northwest by 54 G4M bombers was also successful: all but four of the 3^rd Pursuit Squadron’s P-40 fighters, short of fuel and caught in their landing pattern, were destroyed in combat or by lack of fuel. Some 12 P-40 fighters from the 20^th (four), 21^st (two), and 3^rd (six) Squadrons attacked the strafing aircraft but with little success, losing at least four of their own number.

The Far East Air Force lost half its aircraft in the 45-minute attack, and was all but destroyed over the next few days, the losses including a number of the surviving B-17 bombers lost to take-off crashes of other aircraft. The 24^th Pursuit Group flew its last interception on 10 December, losing 11 of the 40 or so P-40 machines that took off, and the surviving Seversky P-35 single-eat fighters of the 34^th Pursuit Squadron were destroyed on the ground at Del Carmen. That night the Far East Air Force’s combat strength had been reduced to 12 operational B-17, 22 P-40 and eight P-35 machines. Fighter strength fluctuated daily until 24 December, when USAFFE ordered all its forces into Bataan. Until then P-40 and P-35 fighters were cobbled together from spare parts taken from wrecked aircraft, and still-crated P-40E fighters were assembled at the Philippine Air Depot. Clark Field was abandoned as a bomber field on 11 December after being used as a staging base for a handful of B-17 missions. Between 17 and 20 December, the 14 surviving B-17 bombers were withdrawn to Australia. Every other aircraft of the FEAF was destroyed or captured.

No formal investigation looked into this failure as it occurred in the aftermath of Pearl Harbor. After the war, Brereton and Sutherland in effect blamed each other for the Far East Air Force being taken by surprise on the ground, and MacArthur released a statement that he had no knowledge of any recommendation for B-17 attacks on Formosa.

The 14^th Army began its 'M' invasion with a landing on Batan island (not to be confused with the Bataan peninsula), 120 miles (190 km) off Luzon’s northern coast, on 8 December, by naval infantry units. Landings on Camiguin island and at Vigan, Aparri and Gonzaga in northern Luzon followed two days later.

Two B-17 bombers attacked the Japanese ships offloading at Gonzaga, and other B-17 bombers with fighter escort attacked the landings at Vigan. In this last co-ordinated action of the Far East Air Force, US aircraft damaged two Japanese transports. the Oigawa Maru and Takao Maru, the cruiser Naka, and the destroyer Murasame, and sank the minesweeper W-10.

Early in the morning of 12 December, the Japanese landed 2,500 men of the 16^th Division at Legazpi in the southern part of Luzon, 150 miles (240 km) from the nearest US and Philippine forces. The attack on Mindanao followed on 19 December, using elements of Lieutenant General Hitoshi Imamura’s 16^th Army from the Palau islands group on temporary attachment to the invasion forces to permit the 14^th Army to use all its troops on Luzon.

Meanwhile, Hart withdrew most of his Asiatic Fleet from Philippine waters following Japanese air attacks that inflicted heavy damage on the US naval facilities at Cavite on 10 December. Only submarines were left to contest Japanese naval superiority, and the commanders of these boats, conditioned by pre-war doctrine that held the fleet submarine to be a scouting vessel more vulnerable to air and anti-submarine attack than it actually was, proved unequal to the task. Because of this erroneous doctrine for submarine warfare and the infamous failures of the Mk 14 torpedo that plagued the US submarine fleet for the first two years of the Pacific War, not a single Japanese warship was sunk by the Asiatic Fleet during the Philippines campaign.

The Japanese main attack began early on the morning of 22 December as 43,110 men of the 48^th Division and one regiment of the 16^th Division, supported by artillery and approximately 90 tanks, landed at three points along the eastern coast of Lingayen Gulf. A few B-17 bombers flying from Australia attacked the invasion fleet, and US submarines harassed it from the adjacent waters, but to little effect.

Wainwright’s poorly trained and equipped 11^th Division (Philippine Army) and 71^st Division (Philippine Army) could neither repel the landings nor pin the Japanese on the beaches. The remaining units of the Japanese divisions landed farther to the south along the gulf. The 26^th Cavalry of the well-trained and better-equipped Philippine Scouts, advancing to meet them, put up a strong fight at Rosario, but was forced to withdraw after taking heavy casualties with no hope of sufficient reinforcements. By the fall of night on 23 December, the Japanese had moved about 10 miles (16 km) into the interior. On the following day, 7,000 men of the 16^th Division landed at three locations along the shore of Lamon Bay in southern Luzon, where they found Parker’s forces dispersed, and without artillery protecting the eastern coast, unable to offer serious resistance. They immediately consolidated their positions and began the drive to the north toward Manila, where they were to link with the forces advancing to the south in the direction of the capital for the final victory.

The US Philippine Division moved into the field in reaction to reports of airborne drops near Clark Field, and when this proved false, was deployed to cover the withdrawal of troops into the Bataan peninsula and to resist Japanese advances in the Subic Bay area.

On 24 December, MacArthur invoked the pre-war War Plan Orange 3, which called for use of five delaying positions in central Luzon while the main forces withdrew into the Bataan peninsula. This was carried out in part by the 26^th Cavalry Regiment. MacArthur relieved Parker of his command of the South Luzon Force and had him begin preparing defensive positions on the Bataan peninsula, using units as they arrived; both the military headquarters and the Philippine’s government were moved there. Nine days of feverish movement of supplies into the Bataan peninsula, primarily by barge from Manila, began in an attempt to feed an anticipated force of 43,000 troops for six months, but ultimately 80,000 troops and 26,000 refugees flooded the peninsula. Nevertheless, substantial forces remained in other areas for several months.

On 26 December, Manila was declared an open city by MacArthur, but the US military was still using the city for logistical purposes and the Japanese army ignored the declaration and bombed the city.

Units of both defence forces were manoeuvred to hold open the escape routes into the Bataan peninsula, in particular San Fernando, the steel bridges at Calumpit over the deep Pampanga river at the northern end of Manila Bay, and Plaridel to the north of Manila. Despite its inexperience and equivocating orders to withdraw and hold, the South Luzon Force successfully executed retrograde 'leapfrogging' tactics and had crossed the bridges by 1 January. Japanese air commanders rejected appeals by the 48^th Division to bomb the bridges to trap the retreating forces, which were subsequently demolished by Philippine Scout engineers on 1 January.

The Japanese realised the full extent of MacArthur’s plan on 30 December and ordered the 48^th Division to press forward and seal off the Bataan peninsula. In a series of actions between 2 and 4 January, the 11^th and 21^st Divisions of the Philippine army, the 26^th Cavalry (Philippine Scouts) and the US M3 Stuart light tanks of the Provisional Tank Group held open the road from San Fernando to Dinalupihan at the neck of the peninsula for the retreating forces of the South Luzon Force, then made good their own escape. Despite 50% losses in the 194^th Tank Battalion during the retreat, the Stuart tanks and a supporting battery of M3 gun motor carriages armed with 75-mm (2.95-in) guns repeatedly stopped Japanese thrusts and were the final units to enter the Bataan peninsula.

On 30 December, the US 31^st Infantry moved to the vicinity of Dalton Pass to cover the flanks of troops withdrawing from central and southern Luzon, while other units of the Philippine Division organised positions at Bataan. The 31^st Infantry then moved to a defensive position on the west side of the road linking Olongapo and Manila, near Layac Junction at the neck of the Bataan peninsula on 5 January. The junction was given up on 6 January, but the withdrawal into the Bataan peninsula had been successful.

Between 4 and 7 January, the Japanese concentrated on reconnaissance and preparations for an attack on the Main Battle Line between Abucay to tp Mauban via Mt Natib. At the same time, in what was later seen as a critical mistake, they also relieved the 48^th Division, responsible for much of the success of Japanese operations, with the considerably less capable 65^th Brigade, which had been created as a garrison rather than combat force. The 5^th Air Group was withdrawn from operations on 5 January in preparation for its movement with the 48^th Division to the Netherlands East Indies. US and Filipino forces repelled night attacks near Abucay, and elements of the Philippine Division counterattacked on 16 January. This failed, and the division withdrew to the Reserve Battle Line between Casa Pilar and Bagac in the centre of the peninsula on 26 January.

The 14^th Army renewed its attacks on 23 January with an attempted amphibious landing behind the lines by a battalion of the 16^th Division, then with general attacks beginning on 27 January along the Main Battle Line. The amphibious landing was disrupted by a PT-boat and contained in brutally dense jungle by ad hoc units made up of USAAF personnel, naval personnel and the Philippine Constabulary. The pocket was then slowly forced back to the cliffs, with considerable losses on each side. Landings to reinforce the surviving pocket on 26 January and 2 February were severely disrupted by air attacks from the few remaining FEAF P-40 warplanes, then trapped and eventually annihilated on 13 February.

A penetration of the I Corps line was stopped and broken up into several pockets. On 6 February, Homma ordered the suspension of offensive operations in order to reorganise his forces. This could not be carried out immediately as the 16^th Division remained engaged trying to extricate a pocketed battalion of its 20^th Regiment. With further losses, the 378 remaining men of the battalion were extricated on 15 February. On 22 February, the 14^th Army's line was withdrawn a few miles to the north and USAFFE forces re-occupied the abandoned positions. The result of the 'Battle of the Points' and 'Battle of the Pockets' was total destruction of all three battalions of the 20^th Regiment and a clear USAFFE victory.

For several weeks the Japanese, deterred by heavy losses and reduced to a single brigade, undertook siege operations while awaiting rehabilitation and reinforcement. Both armies engaged in patrols and limited local attacks. Because of the worsening Allied position in the Asian and Pacific regions, US President Franklin D. Roosevelt ordered MacArthur to relocate to Australia as the Supreme Allied Commander South-West Pacific Area, and Wainwright assumed command of what was now termed the US Forces in the Philippines on 23 March. During this period, elements of the Philippine Division were shifted to assist in the defense of other sectors.

Beginning on 28 March, a new wave of Japanese air and artillery attacks hit the Allied forces, which had by now been severely weakened by malnutrition, sickness and prolonged fighting. On 3 April, the Japanese began to break through along Mt Samat, estimating that the offensive would require a month to end the campaign. No longer operating as a co-ordinated unit and exhausted by five days of nearly continuous combat, the Philippine Division was unable to counterattack effectively against heavy Japanese assaults. On 8 April, the US 57^th Infantry (Philippine Scouts) and the 31^st Division (Philippine Army) were overrun near the Alangan river. The US 45^th Infantry (Philippine Scouts), under orders to reach Mariveles for evacuation to Corregidor island, finally surrendered on 10 April, and only 300 of the 31^st Infantry’s men reached Corregidor island.

Corregidor, which included Fort Mills, was a US Army Coast Artillery Corps position defending the entrance to Manila Bay, part of the Harbor Defenses of Manila and Subic Bays. Its armament included both older sea-coast disappearing gun batteries of the 59^th and 91^st Coast Artillery Regiments (the latter a Philippine Scouts unit), an offshore mine field of some 35 groups of controlled mines,] and one anti-aircraft unit, the 60^th Coast Artillery (AA). The last was posted on the higher elevations of Corregidor and was able to respond successfully to the Japanese air attacks, downing many fighters and bombers. The older stationary batteries with fixed mortars and immense guns for defence against attack from the sea, were easily put out of commission by Japanese bombers. The US troops and Philippine Scouts defended the small fortress until they had little left with which to wage a continued defence.

Early in 1942, the Japanese air command installed oxygen equipment in its bombers so that they could fly higher than the maximum altitude attainable by Corregidor’s anti-aircraft batteries, and after that heavier Japanese bombardment began.

In December 1941, Philippine President Manuel L. Quezon, MacArthur and other high-ranking military officers and diplomats together with their families had escaped the bombardment of Manila to be accommodated in Corregidor island’s Malinta Tunnel. Before their arrival, Malinta’s lateral tunnels had served as high command headquarters, hospital and storage of food and weapons. In March 1942, several US Navy submarines arrived on the northern side of Corregidor bringing mail, orders and weaponry, and taking away with them high=ranking US and Filipino government officials, gold and silver, and important records. Those who were unable to escape by submarine later became prisoners of war in Japanese camps or were placed in civilian concentration camps in Manila and other locations.

Corregidor island was defended by 11,000 men, comprising the units mentioned above that were stationed on Corregidor, the 4^th Marines and US Navy personnel deployed as infantry. Some were able to get to Corregidor from the Bataan peninsula when the Japanese overwhelmed the units on the mainland. The Japanese began their final assault on Corregidor with an artillery barrage on 1 May. On the night of 5/6 May, two battalions of the 61^st Regiment landed at the north-eastern end of the island. Despite strong resistance, the Japanese established a beach-head that was soon reinforced by tanks and artillery. The defenders were quickly pushed back toward the stronghold of Malinta Hill.

Late on 6 May, Wainwright asked Homma for terms of surrender, and the Japanese army commander insisted that surrender include all the Allied forces in the Philippine islands group. Believing that the lives of all those on Corregidor would otherwise be endangered, Wainwright accepted. On 8 May, Wainwright sent a message to Sharp, ordering him to surrender the Visayan-Mindanao Force. Sharp complied, but many individuals carried on the fight as guerrillas. Few unit commanders were so hard pressed as to be forced to surrender and none had any desire to surrender. Sharp’s decision to surrender involved many factors inc;uding his belief that the Japanese might otherwise execute the 10,000 survivors of Corregidor, and that he now knew that his forces would not be reinforced from the USA as had previously been thought.

The defeat was the beginning of three and a half years of harsh treatment for the Allied survivors, including atrocities such as the 'Bataan Death March' and the misery of Japanese prison camps, and the 'hell ships' on which US and other Allied prisoners were sent to Japan to be used as slave labor in mines and factories. Thousands were crowded into the holds of Japanese ships without water, food or sufficient ventilation. The Japanese did not mark 'POW' on the decks of these vessels, and some were attacked and sunk by Allied aircraft and submarines: on 7 September 1944, for example, the transport Shinyo Maru was torpedoed and sunk by the US submarine Paddle with losses of 668 prisoners of war; only 82 prisoners of war survived. Although the campaign had been a victory for the Japanese, it took longer than anticipated to defeat the Filipinos and Americans. This required forces earmarked for use in the attacks on Borneo and Java to be diverted to the 'Battle in the Philippine Islands', and also slowed the advance on New Guinea and the Solomon islands group.

During the occupation of the Philippine islands group, US and Filipino guerrillas fought against the occupying forces. The Allied and Philippine Commonwealth forces began the campaign to recapture the Philippine islands group in 1944 with the 'King II' landings on the island of Leyte.

The defence of the Philippines was the longest resistance to the Imperial Japanese army in the initial stage of World War II. After the 'Battle of Abucay', the Japanese started to withdraw from Bataan, and resumed their attack in April, thus allowing MacArthur and the Australian forces some 40 days in which to prepare Australia as an operational base and organise its defence. Filipino and US resistance to the Japanese up to the fall of the Bataan peninsula on 9 April 1942 lasted 105 days.