The majority of the doctrine currently published by the U.S. Army Special Operations Command intended to guide operators in conducting Unconventional Warfare (UW) focuses overwhelmingly on training and employing a "guerrilla force." But how are these guerrillas recruited and, once enlisted, how are they equipped, paid, and sustained? The answer for successful guerrilla movements in the past has been a well organized resistance underground. In this thesis I will examine the underground movements that provided UW resistance fighters during two wars; the three underground movements in the Philippines that continued to fight Japan between MacArthur's hasty departure and triumphant return and the resistance movement in South Vietnam that vexed American forces between the partitioning of the country in 1954 until the U.S. departure in 1974.