The Shimbu group situated in the mountains and hills east of Manila controlled extremely important installations of the Metropolitan water supply system. Under Gen Shizuo Yokohama, the 50,000 strong Shimbu group fought with the Allies all throughout the early months of 1945.
Due to huge water shortages and unsanitary conditions in Metro Manila, US General MacArthur, head of the United States Military Forces in the Pacific, ordered US Gen. Walter Krueger via radio on 10 April 1945 to seize Ipo Dam and the surrounding lands from the hands of the Japanese. Gen. Krueger tasked the US 43rd Division headed by General Wing to launch the operation.
Hiding in the area directly surrounding Ipo Dam were thousands of Japanese infantry. Some of those were situated on the road to the damn and retreated at night to the safety of Pinagrealan Cave, where they had a ready water supply, access to shelter and were safe from the US Forces.
The Allied Forces attacked Ipo Dam on the night of 6th May which completely surprised the outer defenses of the Japanese. The 169th, 172nd and 103rd Divisions attacked from the South as elements of the 169th Infantry and the Markings regiment attacked from the western sector. The 1st “Yay” Regiment and the 1st Battalion of the 2nd “Yay” Regiment of the Marking’s guerilla unit gathered in Angat, Bulacan. The Markings combated in a small engagement against the Japanese Mapuya Signal Corps in the Hill 21 and killed around nine Japanese soldiers.
The first fierce fight erupted on Hill 535 where elements of the Markings and Kasama Battalion clashed to capture the strategic area. By 12th May, Markings in the northern sector broke through the strongly defended Japanese positions after the heavy air and artillery bombardment. Throughout the battle, hundreds of fighter bombers from the Fifth Air Force dropped gallons of napalm to destroy enemy defensive positions and demoralized the Japanese troops.
On 19 May 1945, during WWII, the dam was finally saved from the Japanese in the Battle of Ipo Dam. “Marking’s Guerrillas” Yay Regiment, under the command of Col. Marcos V. Agustin, and the 43rd Division, supported by the Fifth Air Force, captured the water source intact from the Japanese defenders.
Remnants of World War II era bullets and military equipment occasionally turn up in the areas surrounding Pinagrealan Cave.
We cannot allow rich and powerful people to destroy the environment for their own benefit.
Our history is too important!
Save Pinagrealan Cave!
Filipino people must come first, before money, politics, and power!