I Corps Bolsters Retaking the Philippines in 1945

JOINT BASE LEWIS-MCCHORD, Wash. — Eighty years ago, on Jan. 9, 1945, I Corps landed on the beaches of northern Luzon at Lingayen Gulf, playing a pivotal role in defeating the Imperial Japanese Army (IJA) and ultimately threatening the Japanese home islands. During its planning, headquarters staff officers of Gen. Douglas MacArthur’s Southwest Pacific Area (SWPA) referred to the campaign as MUSKETEER, but during its execution, they codenamed it MIKE.

The overall intent of MacArthur’s operation was not only to cut access to the Japanese-occupied “Southern Resource Area” around Indonesia but, more importantly, to return the Philippines to its people. I Corps, under Gen. Walter Krueger’s Sixth Army, was tasked by MacArthur to block the most significant IJA force in the jungle-covered mountains of Luzon as a part of the biggest land operation in the Pacific during World War II.

Its success resulted not from “multi-domain operations” but from the joint dominance of the air and sea, constructive partnerships with local guerillas, and the overwhelming Allied logistical support on the ground.

Gen. Tomoyuki Yamashita of the 14th Area Army, the commander of all Japanese forces in the Philippines with at least 250,000 troops on Luzon, adopted an attritional plan to tie down and delay as many American forces as possible because he realized that his isolation on Luzon was complete. There would be no resupply or reinforcements able to reach him because of the earlier defeat at the naval battle of Leyte Gulf. As a result, the Imperial Japanese Navy could no longer pose a serious threat at sea and devastating U.S. attacks on airfields from Formosa to the Philippines ensured American air superiority from both carriers and land bases.

The scattered kamikaze attacks on the Jan. 9 landing force could not stop the enormous armada of 7,000 U.S. and Australian ships and over 200,000 U.S. Army Soldiers. This Pacific invasion force even eclipsed the combined Allied numbers at the Normandy D-Day landings seven months earlier in Europe.

After augmentation from the 1st Cavalry Division, the rest of the Sixth Army fought south from their northern beachheads toward Manila. However, it took another 30 days to capture the strategic port city at an enormous cost in U.S. casualties.

Despite American military advantages, the tragic destruction of Manila occurred as Japanese defenders fought to the death, leading to the deaths of more than 100,000 civilians. I Corps was not involved in the house-to-house urban combat in Manila, nor could it maneuver in the open Central Plain of Luzon, as its mission was to defeat the enemy in the northern mountains.

When Krueger tasked Maj. Gen. Innis P. Swift, commander of I Corps, to protect the Sixth Army’s advance to Manila by blocking the Shobu Group in northern Luzon, they did not accurately anticipate how numerous and how singularly focused the Japanese would adhere to their attritional strategy to delay the American advance from their mountainous jungle redoubts.

Yamashita split his forces into three geographic areas: the Kembu Group (30,000 strong) to defend Clark Field into the western Zambales Mountains, the Shimbu Group (80,000 strong) to defend Manila down into the southern Bicol Peninsula and the Shobu Group (152,000 strong and commanded by Yamashita himself) to defend northern Luzon in the Cordillera Central and Sierra Madre Mountains.

Once the initial blocking operation to protect the XIV Corps’ drive to Manila was complete in late Feb., I Corps attacked into the teeth of IJA defenses with the 33rd and 37th Infantry Divisions cracking the hard nut of Baguio, where Yamashita initially set up his headquarters for the American assault. Simultaneously, the 32nd and 25th Infantry Divisions attacked towards Santa Fe to smash the Shobu Group’s defenses around Balete Pass.

Yamashita blunted the effective firepower of artillery and airstrikes as well as the mobility of his opponents by creating a layered defense using ridge after ridge. In response, I Corps soldiers used flamethrowers and napalm to burn out the enemy and blow up cave entrances to trap the Japanese in their dug-out positions. However, due to the arduous mountain-jungle terrain, oppressively hot and humid climate and the entrenched IJA forces, progress could only be measured in weeks as I Corps crept north toward the Cagayan River Valley.

With the I Corps’ infantry divisions directly attacking the IJA defenses into the center of northern Luzon for a monthslong effort, Gen. Swift organized a separate effort to envelop Yamashita’s dwindling force by indirectly maneuvering around the Northwest coast toward the northern end of the Cagayan Valley.

Named after its commander, Maj. Robert V. Connolly, the task force was composed of companies from the 6th Ranger Battalion, the 32nd Infantry Division’s 127th Infantry Regiment, and the 694th Field Artillery Battalion. Crucially, it was paired with a battalion from the 11th Regiment of the U.S. Army Forces in the Philippines (Northern Luzon), or USFIP (NL), which consisted of a combined U.S. Army and Filipino guerilla force that had been resisting the Japanese occupation since 1942 and was now supplied by Krueger’s Sixth Army.

The task force’s northern drive on the coastal highway to Aparri from June 6-11 proved to be quick due to the effective clearance of enemy forces previously by USFIP (NL). When they arrived at their objective, they continued to attack the rear elements of Yamashita’s Shobu Group.

Throughout the campaign, Filipino guerillas provided invaluable assistance in the fight to liberate Luzon—they excelled in not only sabotage and reconnaissance but also serving as light infantry to guide and augment U.S. Army attacks, such as with TF Connolly, and especially to facilitate the liberation of prisoner-of-war camps such as Cabanatuan in late Jan.

Additionally, their ability to successfully interact and influence the civilian population, already inimical to the Japanese occupiers, multiplied the impact of U.S. combat operations across the islands during the campaign. Task Force Connolly showcased not only Army improvisation with a composite force but also the vital need to partner with local forces to ensure success.

The sustainment of all these combined forces became an immense task once on-the-ground forces swelled in the summer of 1945. Almost 900,000 soldiers were now assigned to MacArthur’s SWPA command, with over a third of that number in Luzon. SWPA brought in new service units and set up supply depots at San Fernando (just north of Lingayen Gulf landings) and Manila (once it was completely repaired and restored).

The 1350th Engineer Base Depot Group, a forerunner unit of the 593rd Expeditionary Sustainment Command, moved from Leyte to Luzon to support the enormous supply mission growing in Manila harbor. Once the capital city was secure in early March, initial cargo unloaded and processed that month only accounted for 143,186 tons of material. However, by July, it had increased by four times that amount. Designated “Base X” by the supply command, the Manila base had already become the most extensive American logistical base in the SWPA.

To sustain operations and aid in rebuilding Manila, Army logistical units warehoused and distributed massive stocks of food, water, fuel, medical supplies, and construction materials. Maintenance and operations of railroads and highways became an essential task. However, over 5 million tons of supply were airdropped during Luzon operations, including to I Corps units in the north. Again, the local Filipino population assisted not only when carrying parties were needed to reach remote units in contact, but they also served as the majority of the manual labor used to reconstruct facilities destroyed by the Japanese. Together, U.S. and Filipino efforts sustained the fight and the restoration of Luzon.

In the face of inevitable defeat, the Shobu Group continued to fight a delaying retreat further into the northern mountains until Aug. 15, and just when they were on the verge of starvation, the official surrender of the Government of Japan ended combat. Gen. Yamashita was tried for war crimes related to the massacres in Manila, Palawan, and Singapore. Despite the debate over his direct responsibility, he was convicted and executed in Luzon 17 months after his surrender. However, the Japanese strategy to “delay by destruction” on Luzon would prove utterly horrific for everyone involved: over 200,000 Japanese and 10,000 Americans were killed from combat, disease, or deprivation—with the Filipinos suffering most as thousands died and were displaced by the violence.

While the liberation was bittersweet, Allied POWs released from various horrible locations by combined forces resulted in joyous reunifications. I Corps’ hard-fought victory on Luzon was not the result of multi-domain operations, but rather effective joint and combined operations, supported by a robust sustainment network and the invaluable partnership of Filipino forces.

For additional reading:

CMH Pub 72-28, Luzon 1944-1945
Samuel Eliot Morison, The Liberation of the Philippines (1963)
Robert Ross Smith, Triumph in the Philippines (1963)
Jon Diamond, The Liberation of the Philippines: Rare Photographs from Wartime Archives (2021)