  the philippines campaign (filipino:labanan sa pilipinas) or the battle of the philippines was the invasion of the philippines by japan in 1941â1942 and the defense of the islands by filipino and united states forces. the defending forces outnumbered the japanese invaders by 3 to 2, but were a mixed force of non-combat experienced regular, national guard, constabulary, and newly created commonwealth units; the japanese used their best first-line troops at the outset of the 
1941_in_military_history 1941_in_the_Philippines 1942_in_military_history 1942_in_the_Philippines Battles_involving_Philippine_Commonwealth_Army Campaigns_of_World_War_II Invasions_by_Japan Invasions_of_the_Philippines Military_history_of_the_Philippines_during_World_War_II South_West_Pacific_theatre_of_World_War_II United_States_Marine_Corps_in_World_War_II World_War_II_invasions