As an indicator of USFIP strength on Mindanao, during January and February 1945, in preparation for the return of regular American forces, the guerrillas seized the Dipolog airstrip in northern Zamboanga and held it while surrounded by the Japanese. With the arrival of regular American forces in March 1945, Fertig's guerrilla forces participated in the Battle of Mindanao that effectively ended organized Japanese resistance on that island. They then disbanded. On September 15, 1945, the 6th Infantry Division of the Philippine Army was reactivated, and its ranks were heavily seeded with Filipino veterans of the USFIP at all levels of command.