Map Description

History Map of WWII:

The Philippine Islands: Leyte Island and the Visayas 1944/45


Illustrating:

Sixth Army Operations on Mindoro and Marinduque Islands

13 December 1944 - 24 January 1945

Between 15 December 1944 and 24 January 1945, the U.S. Sixth Army conducted amphibious and follow-up operations on Mindoro, and to a more limited and less formally documented extent, Marinduque Island. These actions formed part of the broader campaign to liberate the Philippines from Japanese occupation and were strategically connected to the earlier Leyte landings and the impending main assault on Luzon.

The principal objective of the Mindoro operation was to secure airfields and logistical bases to support fighter and medium bomber operations essential to the forthcoming landings at Lingayen Gulf.

It should be noted that the principal combat phase of the Mindoro operation began on 15 December 1944, not 13 December. The date of 13 December actually marks significant kamikaze attacks, particularly the one that severely damaged USS Nashville, the flagship of Rear Admiral Struble's amphibious force. This distinction is confirmed in Dictionary of American Naval Fighting Ships (DANFS) and Sixth Army's action reports.



:: Strategic Background and Terrain Considerations ::

The campaign to retake the Philippines formally began with General Douglas MacArthur's landing on Leyte on 20 October 1944.

Leyte offered a central staging ground but presented severe challenges for sustained air operations due to poor terrain and seasonal monsoon weather. Despite its value as a foothold, Leyte's airfields proved unsuitable for medium and heavy bombers, and many became unserviceable due to flooding, as documented in Appleman's "Leyte" in the Center of Military History series.

To prepare for the large-scale amphibious landings on Luzon, especially at Lingayen Gulf (planned for 09 January 1945), forward air bases within tactical range were urgently needed. Mindoro, situated southwest of Luzon and west of Panay, was selected for its relatively light Japanese garrison, favorable terrain for airfield construction, and access to Mangarin Bay, the best anchorage in the region. These factors made it ideal for hosting fighter escort squadrons, tactical bomber groups, and logistical nodes.



:: Landing Forces and Command Structure ::

The main landing occurred near San Jose on Mindoro's southwestern coast. The area was chosen for its access to Mangarin Bay and its suitability for airfield development on level ground.

Regarding the order of battle, historical records indicate that the landing was conducted specifically by the 19th Infantry Regiment of the 24th Infantry Division, alongside the 503rd Parachute Regimental Combat Team (PRCT). Contrary to what might be assumed from the unit designations, both units landed by sea rather than air, due to the lack of suitable runways on Leyte from which a parachute drop could be mounted, as documented in the Center of Military History series by Greenfield, Palmer, and Wiley.

The operation was commanded by Lt. Gen. Walter Krueger of the Sixth Army, with naval support from the Seventh Fleet under Admiral Kinkaid and air support from the Fifth Air Force.



:: Japanese Defenses and Combat Assessment ::

Japanese ground resistance on Mindoro was limited. Defending forces consisted of approximately 1,000–1,200 personnel, mostly from fragmented or rear-area units.

It should be clarified that U.S. Army and Japanese sources do not support the presence of the Imperial Japanese 8th Division on Mindoro. The defenders were primarily scattered elements from logistical detachments, naval units, and base forces — not front-line infantry divisions, as documented in Morton's work in the Center of Military History series and the Japanese Monograph Series.

The U.S. advance was rapid and bypassed many isolated defenders. These stragglers were either killed, captured, or driven into Mindoro's interior, where some remained cut off for weeks.



:: Airborne Threats and Kamikaze Campaign ::

While ground resistance was light, the major Japanese response came from the air. Kamikaze attacks, which had intensified since the Battle of Leyte Gulf in October 1944, targeted the invasion fleet.

On 13 December, the USS Nashville was struck by a kamikaze, resulting in 133 killed and 190 wounded, as recorded in DANFS. Later, on 04 January 1945, the escort carrier USS Ommaney Bay was sunk by another kamikaze while supporting Mindoro-based operations for the Luzon landings, with 95 sailors killed according to Naval Historical Center records.

Despite these losses, the amphibious landing on Mindoro proceeded as planned and encountered minimal disruption.



:: Casualties ::

Regarding casualties, it should be noted that precise U.S. Army ground casualties on Mindoro are not individually reported in official sources, but all indicators suggest they were low — fewer than 100 total according to Appleman and Sixth Army After Action Reports.

Naval casualties, particularly from kamikaze strikes, were significantly higher.

Japanese losses were approximately 200 killed and 15 captured, with several hundred more believed to have been isolated or rendered combat-ineffective.

These numbers are post-action estimates, not confirmed counts, and should be regarded as approximations.



:: Airfield Construction and Strategic Utility ::

Once secured, Mindoro's airfields were rapidly constructed. The first airstrip near San Jose was operational within five days of the landing (by approximately 20 December). A second airstrip became operational within 13 days, by 28 December, providing immediate support for the Luzon landings on 09 January 1945, as documented in "U.S. Army Engineers in WWII" from the Center of Military History.

These airfields housed fighter groups, reconnaissance squadrons, and medium bombers, providing both air cover and tactical bombing for operations on Luzon.



:: Marinduque ::

U.S. forces landed on the island on January 3, 1945, following the Japanese withdrawal on December 21, 1944. The operation, involving Company K of the 21st Infantry Regiment, was executed without opposition and aimed at establishing radar installations and securing the island. Subsequent actions included coordinated efforts with local guerrillas to eliminate remaining Japanese resistance, particularly in Boac.



:: Strategic Outcome ::

The Mindoro operation was tactically swift and strategically vital. Its successful execution provided forward basing for the Fifth Air Force, enabled continuous fighter escort and air support for the Luzon landings, and demonstrated a textbook application of joint and combined arms doctrine.

Simultaneously, U.S. and Filipino operations across the Visayas (Panay, Cebu, Samar, Leyte) continued to isolate and neutralize Japanese garrisons, cutting internal supply lines and preventing reinforcement.

Between 15 December 1944 and 24 January 1945, the U.S. Sixth Army's seizure of Mindoro — augmented by guerrilla-led clearance of surrounding islands like Marinduque — provided a critical operational hinge for the liberation of Luzon. It stands as a demonstration of the U.S. island-hopping strategy's effectiveness when leveraging speed of assault, integrated air-ground-sea planning, and rapid engineering follow-up. Mindoro's capture was not only a tactical success but also a strategic enabler, helping to break Japanese control in the Philippines and setting the stage for the largest land battle of the Pacific War, the Battle of Okinawa.

This battle, codenamed Operation Iceberg, began with the Allied invasion of Okinawa on April 1, 1945, and lasted until June 22, 1945.

Credits

Courtesy of the United States Military Academy Department of History.

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