Samar Brigade M1918 Browning .30 caliber automatic rifles M1923 Thompson .45 ACP submachine guns M1917 Browning .30 caliber machine guns M2 Browning .50 caliber heavy machine guns Battle of Monkayo 81st Infantry Regiment is a military unit and formation of the Philippine Commonwealth Army activated in August 1941 and fought in Mindanao during early stage of World War II.

In December when hostilities started Lieutenant Colonel Arden Boellner arrived became its senior military instructor.

[3] Regimental staffs are S1, S2 - Captain Marcos Soliman, S3, S4, Signal Officer, Quartermaster, JAG.

In January 1942, it received an order from General Sharp the Visayas-Mindanao Force commander to transferred the Samar Brigade to Mindanao via Surigao.

The men of 1st Battalion were very effective in preventing the Japanese moving northward and contain them with Davao Province and not reaching Agusan Valley.

Lieutenant Colonel William Van Nostrand, who came from Lanao sector with 61st Infantry, arrived and replaced him as regimental commander.

On May 10, 1942, the regiment was still fighting in two fronts Davao and Butuan when order from Mindanao Force headquarters to surrender the following day.