The 'Battle of Corregidor' was fought between Japanese forces and US and Filipino forces for the fortified island of Corregidor in the mouth of Manila Bay, and thus the culmination of the Japanese 'M' (ii) campaign to take the Philippine islands group (5/6 May 1942).

The fall of the Bataan peninsula on 9 April 1942 ended all organised opposition by the US Army Forces in the Far East to the Japanese forces invading Luzon in the northern part of the Philippine islands group. This left the island bastion of Corregidor, with its network of tunnels and formidable array of defensive armaments, along with the fortifications across the entrance to Manila Bay, as the only obstacle remaining to Lieutenant General Masaharu Homma’s 14^th Army. Homma had to take Corregidor as, in US and Filipino hands, the island denied the Japanese use of Manila harbour, which was the finest natural harbour in the Far East.

Officially designated Fort Mills, Corregidor was the largest of four fortified islands protecting the mouth of Manila Bay, and had been fortified before World War I with powerful coastal artillery. Some 3.5 miles (5.6 km) long and 1.5 miles (2.4 km), the tadpole-shaped island was 2 miles (3.2 km) from Bataan. Its widest and only elevated area, known as Topside, held most of the fort’s 56 pieces of coastal artillery and installations. Middleside was a small plateau containing battery positions as well as barracks. Bottomside was the lower area, where a dock area and the civilian town of San Jose were located. The US forces nicknamed Corregidor as 'The Rock' and the 'Gibraltar of the East', comparing it with the British fortress dominating the entrance to the Mediterranean Sea between Europe and Africa.

The tunnel system under Malinta Hill was the most extensive construction on Corregidor, and contained a main east/west passage 826 ft (252 m) long with a 24 ft (7.3 m) diameter, in addition to 25 lateral passages, each about 400 ft (120 m) long, which branched out at regular intervals from each side of the main passage. A separate system of tunnels to the north of this housed the underground hospital, and had 12 lateral tunnels and space for 1,000 beds. The facility could be reached either through the main tunnel or by a separate outside entrance on the north side of Malinta Hill. The US Navy tunnel system, which lay opposite the hospital, under the south side of Malinta Hill, was connected to the main tunnel by an only partially completed low passageway through the quartermaster storage lateral tunnel. To the east of this was the Malinta Tunnel, the location of the headquarters of General Douglas MacArthur and then, after MacArthur’s departure to Australia on 12 March, Lieutenant General Jonathan M. Wainwright. Reinforced with concrete walls, floors, and overhead arches, the Malinta Tunnel was also fitted with blowers to furnish fresh air, and a double-track electric tramway line along the east/west passage. The Malinta Tunnel provided bomb-proof shelters for the hospital, headquarters and various shops, as well as a maze of underground storage area.

Corregidor’s defensive arsenal was formidable, and centred on 45 pieces of coastal artillery and mortars organised into 23 batteries, some 72 anti-aircraft weapons assigned to 13 batteries, and a minefield of approximately 35 groups of controlled mines. The two 12-in (305-mm) guns of Batteries Smith and Hearn, with a horizontal range of 29,000 yards (26520 m) and all-round traverse. were the longest-ranged of all the island’s artillery.

Caballo Island, with Fort Hughes, lies just to the south of Corregidor and was the next largest in area. At about 160 acres (65 ha), the island rises steeply from the bay to a height of 380 ft (120 m) on its western side. Commander Francis J. Bridget commanded the island’s beach defenses with a total of 800 men, of whom 93 were marines and 443 sailors, by the end of April 1942. The island’s coastal artillery numbered some 13 assorted pieces, including a single 14-in (355.6-mm) M1910 field gun, four 12-in (305-mm) M1912 mortars, two 6-in (15152.4-mm) M1908 guns, and two 3-in (76.2-mm) M1903 guns. The island’s anti-aircraft defences were connected with those of Corregidor.

Fort Drum, which lies some 4 miles (6.4 km) to the south of Fort Hughes, was the most unusual of the harbour defences. Military engineers had removed the entire top of El Fraile island down to the water-line and used the island as a foundation for the construction of a reinforced concrete 'battleship' 350 ft (110 m) long and 144 ft (44 m) wide, with exterior walls of concrete and steel between 25 and 36 ft (7.6 and 11 m) thick. The top 'deck' of this concrete 'battleship' was 40 ft (12 m) above the low-water mark and had walls 20 ft (6.1 m) thick. Equipped with four 14-in (355.6-mm) guns in armoured turrets facing seaward, a secondary battery of four casemated 6-in (152-mm) guns, and two anti-aircraft guns, the fort and its 200-man garrison were considered impregnable to.

The last of the bay’s islands is Carabao island, lying only some 500 yards (455 m) from the shore of Cavite province. Except at one point along its eastern shore, the island rises precipitously from the sea in cliffs more than 100 ft (30.5 m) high. The US forces located Fort Frank on this island which, late in 1941, had a military garrison of about 400 men, mostly Philippine Scouts. Its armament consisted of two 14-in (355.6 mm) guns, eight 12-in (305-mm) mortars, four 155-mm (6.1-in) guns, as well as anti-aircraft and beach defence weapons.

All four forts in Manila Bay, as well as Fort Wint in Subic Bay, had been unified before the war into the Harbor Defenses of Manila and Subic Bays, which by August 1941 had became a part of the Philippine Coast Artillery Command. Both were under the command of Major General George F. Moore, who also commanded the Corregidor garrison. The 5,700 men of the Harbor Defense Force were assigned to four coast artillery regiments: the 59^th, 60^th, 91^st and 92^nd, of which the 60^th Coast Artillery was an anti-aircraft artillery unit and the 91^st and 92d Coat Artillery were Philippine Scouts units, plus headquarters and service troops.

About 500 Philippine army soldiers in training were organised into the 1^st and 2^nd Coast Artillery Regiments (Philippine Army), but operated under the control of the two Philippine Scouts regiments. Moore organised the force into four commands for the purposes of tactical control: seaward defense; North and South Channels defence under the command of Colonel Paul D. Bunker; anti-aircraft and air warning defences under the command of Colonel Theodore M. Chase, and Inshore Patrol (the gunboats Oahu and Luzon, the minesweeper Quail and the submarine rescue ship Pigeon) under the command of Captain Kenneth M. Hoeffel of the US Navy’s 16^th Naval District.

After their evacuation from Olongapo in Zambales, close to Subic Naval Base, on 26 December, the 4^th Marines under the command of Colonel Samuel L. Howard became the primary fighting unit on Corregidor island, whose garrison received the largest group of reinforcements right after the fall of Bataan: some 72 officers and 1,173 men from more than 50 different units were integrated and assigned to the 4^th Marines, but few of the reinforcements were trained or equipped for ground combat. By 30 April 1942, the 4^th Marines actually numbered 229 officers and 3,770 men, of whom some 1,500 were actually men of the US Marine Corps.

On 29 December 1941, the defenders of Corregidor received their first aerial bombardment. The attack lasted for two hours as the Japanese destroyed or damaged the hospital, Topside and Bottomside barracks, the US Navy fuel depot and the officers club. Three days later, the island garrison was bombed for more than three hours. Bombing continued periodically for the next four days, but with only two more raids for the rest of January the defenders had a chance to effect a considerable improvement of their positions.

On 3 February 1942 the US submarine Trout reached Corregidor with 3,500 rounds of 3-in (76.2-mm) anti-aircraft ammunition. Along with mail and important documents, Trout was loaded before her departure with 20 tons of gold and silver previously removed from banks in the Philippine islands group.

On 12 March, under cover of darkness, MacArthur, his family and others were evacuated from Corregidor in four PT-boats, which headed for Mindanao, whence MacArthur was eventually flown to Australia, leaving Wainwright in overall command of the US and Filipino forces in the Philippine islands group.

From 29 December to the end of April 1942, and in the face of incessant Japanese aerial, naval and artillery bombardment, Corregidor’s garrison, which comprised the 4^th Marines and combined units from the US Army, US Navy and locally recruited Filipino soldiers, resisted valiantly, inflicting heavy enemy losses in men and aircraft.

The defenders were living on about 30 oz (850 g) of food per day. Drinking water was distributed only twice per day, but the constant bombing and shelling often interrupted the distribution of rations. When the bombardment killed horses, men dragged the carcasses down to the mess hall for consumption. The continued lack of a well-balanced and adequate diet created problems for the garrison, for men weakened and lacked reliable night vision. Seven private ships under orders from the army, loaded with a supply of food, sailed from Cebu island toward Corregidor, but only the Princess reached the island.

The bombardment of Corregidor island by Japanese artillery began immediately after the fall of the Bataan peninsula on 9 April, and became steadily more intense over the next few weeks as more guns were brought up: one day’s shelling was said to equal all the bombing raids combined in terms of the damage inflicted. After an initial response from a 155-mm (6.1-in) battery, Wainwright prohibited counter-battery fire for three days, fearing that there were wounded prisoners of war on the Bataan peninsula, and who might be killed.

Japanese bombing and shelling continued with unrelenting ferocity. Japanese aircraft flew 614 sorties, dropping 1,701 bombs totalling some 365 tons. Joining the aerial bombardment were nine 240-mm (9.45-in) howitzers, 34 149-mm (5.87-in) howitzers and 32 other pieces of artillery, which pounded Corregidor day and night. It was estimated that on 4 May alone, more than 16,000 shells hit Corregidor.

As of about 15 April, the combined strength of the four fortified islands, including US Army, Philippine Scouts, Philippine army, US Marine Corps, US Navy, Philippine navy and civilians, totaled about 14,728 persons.

From April 28, a concentrated aerial bombardment by Major General Kizo Mikami’s 22^nd Air Brigade, complemented by ground artillery sited on Bataan between 1 and 5 May, preceded landing operations.

On the night of 4 May a submarine returning to Australia from patrol evacuated 25 persons. Among these were Colonel Constant Irwin, who carried a complete roster of all US Army, US Navy and US Marine personnel still alive; Colonel Royal G. Jenks, a finance officer with financial accounts; Colonel Milton A. Hill, the inspector general, three other US Army and six other US Navy officers, and about 13 nurses. Included in the cargo sent from Corregidor were several bags of mail, the last to be sent out of the Philippine islands group, and many records and orders of the US Army Forces in the Far East and the US Forces in the Philippines.

Japanese propaganda for the population of the home islands repeatedly declared in this period that Corregidor was about to fall, followed by weeks of silence when it did not happen, and the Imperial General Headquarters finally declared that the resistance was becoming a serious embarrassment.

On 5 May, Japanese forces led by Major General Goro Taniguchi, the commanding officer of the 4^th Division's infantry group, boarded landing craft and barges for the final assault on Corregidor. Shortly before 00.00, intense shelling struck the beaches between North Point and Cavalry Point. The initial landing by 790 Japanese soldiers of the 1/61^st Regiment quickly bogged down in the face of surprisingly fierce resistance by the US and Filipino defenders, whose 37-mm guns exacted a heavy toll on the invasion fleet.

The Japanese landing was rendered very difficult by the strong sea currents between the Bataan peninsula and Corregidor, as well as the layers of oil from ships sunk earlier in the campaign and which now covered the beaches. The Japanese had thus encountered considerable difficulty in landing men and equipment. However, the sheer numbers of the Japanese infantry, equipped with 50-mm 'knee mortar' grenade launchers, eventually forced the defenders back from the beach.

There was to have been another landing on the western end of Corregidor, by the 4^th Infantry Group using the 37^th Regiment and one battalion of the 8^th Regiment, but this had to be cancelled for lack of adequate numbers of landing craft.

The 3/61^st Regiment of 785 Japanese soldiers was not as successful. This unit landed to the east of North Point, where the defensive positions held by the 4^th Marines were stronger. Most of the Japanese officers were soon killed, and the huddled survivors were hit with hand grenades, machine gun fire and rifle fire. Even so, some of the Japanese managed to link with the first invasion force, and together the Japanese moved inland and had captured the Denver Battery by 01.30 on 6 May.

The US forces launched a counterattack to eject the Japanese from the Denver Battery, and this saw the heaviest fighting between the opposing forces, in what was essentially hand-to-hand combat. A few reinforcements managed to reach the 4^th Marines, but the battle became a duel pitting US grenades against accurate Japanese 'knee mortar' bombs. It was soon cleat that the battle would soon go against the marines unless they were reinforced.

By 04.30, Howard had committed his last reserve of about 500 marines, a few sailors and the soldiers of the 4^th Battalion. These reinforcement tried to join the battle as quickly as possible, but Japanese snipers had slipped behind the front lines and all movement proved very costly. To make matters worse, another 880 Japanese reinforcements arrived at 05.30. The 4^th Marines held their positions, but the Americans were losing ground in other areas. The Japanese had a problem of their own, for several crates of ammunition did not make the landing and, as a result, several Japanese attacks and counterattacks were made with fixed bayonets.

The final blow to the defenders arrived at 09.30 when three Japanese tanks of 7^th Tank Regiment were landed and immediately went into action. The men of Denver Battery withdrew into the ruins of a concrete trench a few yards from the entrance to Malinta Tunnel, and at just this moment Japanese artillery delivered a heavy barrage. Aware of the consequences should the Japanese enter and take the tunnel, where there were about 1,000 helpless wounded men, and realising the Malinta Tunnel could not hold out for much longer, Wainright knew that more Japanese would be landed during the following night and decided to sacrifice one more day of freedom in exchange for several thousand lives. In a radio message to President Franklin D. Roosevelt, Wainwright said that 'There is a limit of human endurance, and that point has long been passed.' Howard burned the regimental flag of the 4^th Marines as well as the national colours to prevent their capture, and Wainwright surrendered the Corregidor garrison at about 13.30 on 6 May, when two officers were sent forward with a white flag to carry his surrender message to the Japanese.

The Japanese losses between 1 January and 30 April and from the initial assault landings on May 5/6, were about 900 men dead and 1,200 wounded, while the defenders suffered 800 men dead and 1,000 wounded.

The successful invasion of Luzon by the Japanese late in December 1941 quickly brought land forces within range of Fort Drum and the other forts in Manila Bay. Just before the outbreak of war in the Pacific, Fort Drum had been restaffed with officers and men of the 59^th Coast Artillery (E Battery). The wooden barracks on the fort’s 'deck' were dismantled to provide an unobstructed field of fire for Battery Wilson.

On 2 January 1942, Fort Drum withstood heavy Japanese air bombardment. On 12 January, an 3-in (76.2-mm) M1903 coastal gun on a pedestal mount was transferred from Fort Frank and installed at Fort Drum to help protect the fort’s vulnerable 'stern' section, and it was named Battery Hoyle. On the next day, before the concrete emplacement was fully dry and the gun had been bore-sighted, it became the first US battery of sea coast artillery to open fire on the Japanese in World War II when it drove off a Japanese-commandeered inter-island steamer, apparently bent on a close inspection of Fort Drum’s vulnerable rear approach. Until that time, the cage mast control tower masked the fire of the rear main turret, while the height of the gun above water created a dead space, even had the field of fire been clear.

In the first week of February 1942, the fort come under sustained fire from Japanese 140-mm (5.87-in) howitzer batteries sited near Ternate on the mainland. By the middle of March, the Japanese had moved heavy artillery into range, opening fire with 240-mm (9.45-in) siege howitzers, destroying Fort Drum’s 3-in (76.2-mm) anti-aircraft battery, disabling one of its 6-in (152.4-mm) guns, and damaging one of the armoured casemates. Sizeable portions of the fort’s concrete structure were chipped away by the shelling.

The armoured turrets were not damaged, however, and remained serviceable throughout the bombardment. Counter-battery fire from Fort Drum’s 14-in (355.6-mm) guns and Fort Frank’s 12-in (305-mm) mortars was ineffective. With the collapse of US and Filipino resistance on the Bataan peninsula on 9 April, only Fort Drum and the other harbour forts remained in US hands.

On the night of 5 May, the 14-in (355.6-mm) batteries of Fort Drum opened fire on the second wave of the Japanese forces assaulting Corregidor, sinking several troop barges and inflicting heavy casualties. Fort Drum surrendered to Japanese forces after the fall of Corregidor on 6 May, and was occupied by them until 1945. Its reinforced concrete roof, 19.7 ft (6 m) thick, enabled Fort Drum to withstand concentrated and frequent pounding from the Japanese from about 15 February to 6 May, and no US personnel in Fort Drum were killed during the siege and only five were injured.

The four 14-in (355.6-mm) turret guns were still firing effectively five minutes before the fall of Corregidor.as at the other forts in the Philippine islands group, Fort Drum’s garrison destroyed the guns before the Japanese took occupation.

The design of Fort Frank included little protection, other than camouflage, against air and high-angle artillery attack. Moreover, most of its heavy ammunition was of the armour-piercing, intended for use against battleships, rather than the high explosive type that would have been more useful against troops and artillery.

Fort Frank was heavily engaged in the final stages of the Japanese seizure of Luzon. On 31 January 1942 the fort’s mortar battery bombarded mainland positions in the Pico de Loro hills, where the Japanese were emplacing artillery, and its 3-in (76.2-mm) uns were also able to engage mainland targets. The Japanese began to bombard Fort Drum and Fort Frank on 6 February 1942. Fort Frank was vulnerable in another way: its normal water supply was from a dam’s reservoir on the Japanese-held mainland. On 16 February the Japanese discovered this and removed part of the pipeline near the dam. Although the fort also had a distillation plant to provide fresh water, this consumed fuel that was also needed for the generators which powered the main batteries' ammunition hoists. The fort’s commander ordered the distillation plant to be started, but also directed a 15-man team to attempt the restoration of the pipeline on 19 February. The team successfully engaged a Japanese patrol but could not get to the pipeline. Eventually another party repaired the pipeline on 9 March. On 20 March, 34 men were killed by Japanese artillery when a round ricocheted into a tunnel at Battery Crofton.

Fort Frank was surrendered, along with all other US forces in the Philippines, on 6 May 1942 after destroying its guns to prevent their use by the Japanese.

During their subsequent occupation of the fort, the Japanese were reportedly able to repair the 14-in (355.6-mm) gun of Battery Crofton and add three 100-mm (3.94-in) guns. In April 1945, during the US liberation of the Philippine islands group, Fort Frank was heavily attacked with 1,000-lb (454-kg) bombs, napalm and other ordnance in preparation for its recapture. On 16 April 1945 the 1/151^st Infantry and Company C of the 113^th Engineer Battalion landed on Fort Frank to find that the Japanese had successfully evacuated the island.

The defeat of Corregidor and the surrender of the other forts in Manila Bay marked the fall of the Philippine islands group and Asia, but Imperial Japan’s timetable for the possible conquest of Australia and the rest of the Pacific Ocean was severely disrupted and ultimately checked in the battles for New Guinea and Guadalcanal, the turning point in the Pacific War.

About 4,000 of the 11,000 US and Filipino prisoners of war from Corregidor were marched through the streets of Manila to incarceration at Fort Santiago and Bilibid Prison. US Army and US Navy nurses continued to work on Corregidor for several weeks, and were then sent to Santo Tomas. The rest were sent by train to various Japanese prison camps. Wainwright was held in Manchukuo. Over the course of the war, thousands more prisoners of war were shipped to the Japanese home islands as slave labourers. While most of the Allied forces on Corregidor surrendered, many individuals continued the fight as guerrillas.

Homma had taken the Philippine islands group in five months rather than the projected two, and was relieved of his command on 1 August 1842 and replaced by Lieutenant General Shizuichi Tanaka.