31^st Infantry Regiment

The 31st Infantry Regiment was the Philippine Division's American infantry regiment and was stationed at Manila before the war. After Japanese forces struck the Philippines in December 1941, the division shifted across Luzon as USAFFE reserve and then into the Bataan defense. The 31st moved to the Zig-Zag area to cover forces withdrawing from central and southern Luzon. From January 3 to 7, 1942, it held west of Olongapo Road near Layac Junction, helping protect the entrance to Bataan while losing Company E and most of the attached 23rd Field Artillery guns.

The regiment next fought in the Abucay-Mount Samat sector as the Philippine Division tried to seal breaks in the Bataan line. On January 16 the 31st and 45th Infantry counterattacked a Japanese penetration in the 51st Division sector. The operation ran into repeated difficulties, and after five days of continuous fighting the counterattacking force was beaten back with heavy losses. On January 26 the division shifted under II Philippine Corps and took responsibility for Sub-Sector D while its infantry regiments were detached for front-line employment.

By early April the starving Bataan garrison was breaking under Japanese air, artillery, and infantry pressure. On April 6 the 31st and 45th counterattacked but failed, and the 31st was destroyed as a combat entity during the withdrawal toward the Mamala River. Remnants reached the Alangan line on April 8 with only about 160 men. Japanese aircraft set fire to the dry grass and bamboo around the position, and infantry pressure struck the exposed line in the afternoon. The regiment fell back at about 1700 and surrendered with the Bataan force on April 9, 1942.