[6][2] After the securing Bataan during the Liberation of the Philippines, the Sixth United States Army under Gen. Walter Krueger was tasked by Gen. Douglas MacArthur on February 7, 1945, to secure the hills east of Manila while moving for a pincer action on the capital with the Eighth United States Army.

Japanese forces under Gen. Yokoyama were able to secure the Balara Filteration Station, and were planning to sabotage the vital facility that provided water to Manila.

The next two days American units fanned out across the line before the foothills of the Sierra Madres facing the Noguchi Force which concentrated around Antipolo.

[5][8][10] Japanese forces created a network of tunnels and artillery sites with strong points at Mounts Oro, Pacawagan, Mataba, and Yabang.

These tunnels and caves would have retractable 105mm and 155mm artillery pieces which would cover the Marikina Valley and lower hills, and would be supported by machine gun nests.

[5][8][11] The American and Philippine forces learning from the New Guinea and Solomon Island campaigns relied on aerial and ground assaults on these strong points.

[5][8] This tactic proved to be highly effective, but still bogged down American forces on each hill for days and event at times weeks.

[5][8] The assault towards Antipolo began with an intensive two-day artillery and aerial bombardment of the southern area of the front.

[2] By March 8, Gen. Griswold commenced the ground attack on Antipolo utilizing the 6th Infantry Division on the north and the 1st Cavalry Division on direct approach from Taytay with the help of the Marking Guerrillas and Hunters ROTC, completing the task by March 11 with a strong push to the east towards Mount Baytangan, and forcing Noguchi to withdraw to his second line of defense.

The attending physician who stabilized Mudge was Dr. James Brownlee Johnson who discovered the use of blood plasma, and who later on would save Hideko Tojo's life after his attempted suicide during the Tokyo War Crimes Trials.

[6][13][14][5] On March 12, in a concerted effort a Japanese formation of four reserve battalions of the Kobayashi Force attempted a counterattack on south of Wawa Dam.

[6][3] Four battalions on March 12 attached to the Kobayashi Force commenced a counterattack towards Marikina on the 6th Division salient, however this was stopped preventing the Japanese to reach their objective.

[2][15][16] On March 14 the 6th Division lost their commanding general, Edwin D. Patrick, who was killed by a Japanese straggler hiding in one of the caves.

[6][5] From April 6 to 9, the 6th Division had slow progress but were able to advance on the southwestern slopes of Mount Mataba, almost a month after their first attempt to capture the area.

This forced a rotation among units, with some elements of the 6th Division to be sent to Manila for garrison duty after a month of fighting in the Rizal area.

[6][8] By early May, the initial intelligence assessment was that the Shimbu Force with over 7,000 casualties has already withdrawn to the east of the Bosoboso River, and that the defense along the Wawa Gorge and the hills to the south were left for delaying action.

Kawashima reluctantly obeyed, and ordered his center unit 358th Independent Infantry Battalion to head south to support Kobayashi in Wawa Dam.

His forces were decimated by intense artillery fire, as well as the largest napalm bombing during the entirety of the Pacific War from an 81-aircraft formation of the Marine Aircraft Groups 24 and 32.

[6] With the collapse of his north and south defensive lines, Gen. Yokoyama ordered the Kobayashi Force to a general retreat on May 22 most of his units ending in the Daraitan area of Tanay, Rizal.