'Mike IV' was a US amphibious landing at Nasugbu on the western side of south central Luzon in the Philippine islands group (31 January 1945).

This landing was undertaken by Major General Joseph M. Swing’s 11^th Airborne Division (less two battalions) of Lieutenant General Robert L. Eichelberger’s 8^th Army otherwise operating in the southern part of the Philippine island group, and its use to approach Manila from the south-west (in an effort outflank the Japanese defences of the Filipino capital) reflected the desire of General Douglas MacArthur to get elements of his South-West Pacific Area forces into Manila as quickly as possible against the forces of Lieutenant General Shizuo Yokoyama’s 'Shimbu' Group of General Tomoyuki Yamashita’s 14^th Area Army.

The operation was based on the use of Rear Admiral William M. Fechteler’s 8^th Amphibious Group to land the 11^th Airborne Division from four troop-carrying destroyer conversions, 35 infantry landing craft and eight medium landing ships near Nasugbu in the area to the south-west of Manila Bay. The 8^th Amphibious Group was escorted by six destroyers of Destroyer Division 5 and three destroyer escorts, and fire support was provided Rear Admiral Ralph S. Riggs’s TG74.2 comprising the light cruiser Denver and destroyers Claxton and Dyson.

On 31 January the Japanese submarine Ro-115 was sunk by the destroyers O’Bannon, Jenkins and Bell and the destroyer escort Ulvert M. Moore in the vicinity of the distant covering force, TG74.3. In an attack by Japanese explosive-filled motor boats, the submarine chaser PC-1129 was sunk; the destroyer Claxton and the destroyer escort Lough beat off more attacks. Lough and the destroyer Conyngham erroneously sank two US small craft, PT-77 and PT-79, on 1 February. To the west of Luzon, the Japanese submarine Ro-55 was severely damaged by the destroyer escort Thomason on 7 February and was probably sunk while trying to return to base by the submarine Batfish on 11 February. The submarine Ro-50, deployed to the south-west of Leyte, sank LST-577 from a supply convoy on 7 February, having missed an earlier target on 1 February. On 13 February the midget submarine Ha-69 twice missed targets inb the area to the west of Mindanao.

On 13 February PT-boats entered Manila Bay for the first time since 1942, and on the same day minesweepers began operations to clear the entrance to the bay.

Rear Admiral Russell S. Berkey’s TG74.3, comprising the light cruisers Boise and Phoenix and the destroyers Fletcher, Hopewell, La Valette and Radford (Destroyer Squadron 21), undertook a gunfire bombardment of the assault area on the southern tip of Bataan and Corregidor, but La Valette and Radford were damaged by mines. On 14 February the bombardment was repeated. Reinforcements from the Australian Commodore H. B. Farncomb’s reserve force arrived in the form of the heavy cruisers Minneapolis, Portland and Australian Shropshire, and six destroyers.

There had been no opposition as the 11^th Airborne Division began to come ashore, and the advance should have been speeded by the dropping of the division’s two remaining battalions to take Tagaytay Ridge. The drop took place only on 3 February, however, and overcame only slight Japanese resistance just as the rest of the division arrived. MacArthur’s plan had been for a rapid overland advance from south of the city as Lieutenant General Oscar W. Griswold’s XIV Corps fought its way from the north, but the 11^th Airborne Division was brought to a halt by Japanese naval troops on the south-western approaches to the city.

Manila had been declared an open city by Yamashita, but its garrison of 16,000 naval personnel of Rear Admiral Sanji Iwabuchi’s 31^st Special Base Force nonetheless decided to hold the city to the last and so prevent the use of its great port by the Americans. Rather than try to fight a battle with central control, Iwabuchi divided his forces into independent battle groups allocated to particular sectors of the city; thus the Americans were committed to the only urban fighting of the Pacific war, though at first Major General Verne D. Mudge’s 1^st Cavalry Division and Major General Robert S. Beightler’s 37^th Division of the XIV Corps were reluctant to admit the fact as they advanced from the north with the immediate objective of securing the camp at Santo Tomas, in which US civilians were interned, before the Japanese decided to murder them. An armoured detachment of the 1^st Cavalry Division liberated this camp on 3 February, and elements of the 37^th Division then pushed on to liberate the civilian internees and military POWs held in Old Bilibid Prison.

By this time the leading units of the XIV Corps had entered the northern suburbs of Manila, and the battle turned into a grim and attritional building-by-building advance as US artillery and house-clearing teams blasted the Japanese back toward the centre of the city.

The leading elements of the 1^st Cavalry Division and 11^th Airborne Division met on 12 February, the day on which the Japanese were left only with Intramuros, the old walled city at the centre of Manila. The Japanese refused to permit the evacuation of civilians, and by the time Manila was finally declared secure by the Americans on 4 March, some 100,000 civilians had become casualties, virtually the entire Japanese naval garrison and some 1,000 Americans had been killed, and the Americans had also suffered about 5,500 wounded.

The 9^th Amphibious Group had meanwhile landed the 151^st Regimental Combat Team and the 34^th Regimental Combat Team of Major General Henry L. C. Jones’s 38^th Infantry Division, totalling 5,300 troops, from 62 landing craft at the southern tip of Bataan on 15 February.

On 16 February the 503^rd Parachute Regimental Combat Team was dropped over Corregidor, to which landing craft delivered one battalion of the 34^th Regimental Combat Team. Support was provided by the destroyers of Destroyer Squadron 49, including Picking, Young and Wickes.

Since 22 January aircraft of Major General Ennis C. Whitehead’s 5^th AAF had dropped 3,200 tons of bombs on the rocky island.

An attack by the Japanese submarine Ro-109 during 17 February on a convoy and its escort was not successful.

With the fall of Manila, the task now facing the 6^th Army was the elimination of the 'Shimbu' Group in the area of Laguna de Bay and in the Bicol peninsula. Yokoyama’s main strength, some 30,000 men, was firmly in command of the southern end of the Sierra Madre mountains as far to the south as Laguna de Bay along the line linking the Ipo Dam, the Wawa Dam and Antipolo. Here the 'Shimbu' Group controlled the water supply to Manila and the direct sea route through the central part of the Philippine islands group, and until the Japanese forces had been winkled out the Americans could neither make full use of Manila harbour not consider the next step forward toward Japan.

In the south of the sector the XIV Corps started a major offensive on 8 March with the 1^st Cavalry Division in the lead until replaced by Major General Leonard F. Wing’s 43^rd Division on 13 March. Supported by Major General Edwin D. Patrick’s 6^th Division from Lieutenant General Innis P. Swift’s I Corps, Griswold’s formation pushed deep into the centre of Yokoyama’s positions until in turn relieved by Major General Charles P. Hall’s XI Corps on 14 March. By the end of March the Americans had reached the eastern side of Laguna de Bay and exposed Yokoyama’s left flank. The 6^th Division failed to take the Ipo Dam and the Wawa Dam during April, but then its successes farther to the south permitted the 43^rd Division to be moved to the 6^th Division’s support for the offensive which began on 6 May, taking the Ipo Dam on 17 May and the Wawa Dam on 28 May.

The remnants of the 'Shimbu' Group fell back to an area north of Dinahican on Luzon’s east coast to the north-east of Manila, and here survived to the end of the war, finally surrendering with 6,300 men.

By this time the maintenance of pressure against the Japanese survivor groups was the task of Eichelberger’s 8^th Army, which on 30 June 1945 assumed responsibility from the 6^th Army so that the latter could be readied for its commitment in the 'Olympic' invasion of Japan.

The last two groups in southern Luzon were offshoots of the 'Shimbu' Group, namely the 'Fuji' Force of 13,000 men commanded by Colonel Fushijige and a unit of some 3,000 men in Luzon’s 'tail' stretching to the south-east from Laguna de Bay. These were tackled by the 1^st Cavalry Division with the aid of Filipino guerrilla forces, which were also heavily involved against the main body of the 'Shimbu' Group. The 'Fuji' Force was hounded to pieces by the end of April, and the rest of the Bicol peninsula fell by 2 May to a concerted drive from the west by the 1^st Cavalry Division and from the east, after a landing at Legazpi on 1 April, by the 158^th Regimental Combat Team.