21st Field Artillery Regiment, a unit of the 21st Infantry Division of the Philippine Army under the USAFFE, was mobilized on 18-November-1941, and was in action from December 1941 to 09-April-1942.

21st Division under Brigadier General Mateo Capinpin was ordered to moved to Lingayen Gulf to prevent any Japanese landings in the area.

21st Field Artillery and other 21st Division units was ordered to withdraw south of Agno river to prepare for a defensive line.

[3] The North Luzon Force under Major General Jonathan Wainwright made a fighting withdrawal and delayed Japanese southward advance towards Manila.

[4] However, the Japanese landing in Lamon Bay gave the USAFFE a scare of South Luzon Force will cutoff activated War Plan Orange 3 effectively.